LASE Abstracts

CONNECTING MINDS. ADVANCING LIGHT.

2016 TECHNICAL SUMMARIES• WWW.SPIE.ORG/PW16

Conferences & Courses 13–18 February 2016 BiOS EXPO 13–14 February 2016 Photonics West Exhibition 16–18 February 2016

Return to Contents

The Moscone Center San Francisco, California, USA

+1 360 676 3290 · [email protected]

1

SYMPOSIUM CHAIRS:

SYMPOSIUM CO-CHAIRS:

Guido Hennig, Daetwyler Graphics AG (Switzerland)

The Moscone Center San Francisco, California, USA

Reinhart Poprawe Fraunhofer-Institut für Lasertechnik (Germany) Koji Sugioka

Yongfeng Lu, Univ. of NebraskaLincoln (USA)

DATES Conferences & Courses 13–18 February 2016

RIKEN (Japan)

Contents 9726: Solid State Lasers XXV: Technology and Devices . . . . . . . . . . . 3

9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI115

9727: Laser Resonators, Microresonators, and Beam Control XVIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

9735: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXI . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

9728: Fiber Lasers XIII: Technology, Systems, and Applications . . . 38

9736: Laser-based Micro- and Nanoprocessing X . . . . . . . . . . . . . . . 139

9729: High Energy/Average Power Lasers and Intense Beam Applications IX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

9737: Synthesis and Photonics of Nanoscale Materials XIII . . . . . . 155

9730: Components and Packaging for Laser Systems II . . . . . . . . . . 74 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV . . . . . . . . . . . . . . . . . . 86 9732: Real-time Measurements, Rogue Events, and Emerging Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 9733: High-Power Diode Laser Technology and Applications XIV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

SPIE is the international society for optics and photonics, a not-for-profit organization founded in 1955 to advanced light-based technologies. The Society serves nearly 225,000 constituents from approximately 150 countries, offering conferences, continuing education, books, journals, and a digital library in support of interdisciplinary information exchange, professional growth, and patent precedent. SPIE provided $3.4 million in support of education and outreach programs in 2014.

2

9738: Laser 3D Manufacturing III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 9741: High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications V . . . . . . . . . . . . . . . . 196

Click on the Conference Title to be sent to that page

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9726: Solid State Lasers XXV: Technology and Devices Monday - Thursday 15–18 February 2016 Part of Proceedings of SPIE Vol. 9726 Solid State Lasers XXV: Technology and Devices

9726-1, Session 1

Mid-IR laser source using hollow waveguide beam combining Ian F. Elder, Daniel H. Thorne, Robert A. Lamb, Selex ES Ltd. (United Kingdom); Richard M. Jenkins, HollowGuide Ltd. (United Kingdom) High brightness laser sources operating in the mid-infrared (wavelengths 2-5 µm) region of the electromagnetic spectrum are of interest for a wide range of applications encompassing medical, defence and remote sensing. A compact, rugged, low-loss beam combiner for combining four wavelengths covering the wavelength range 2.1 µm to 4.6 µm has been designed, manufactured and characterised. The beam combiner consisted of a series of dichroic components integrated into a hollow waveguide optical circuit for confining, combining and directing the optical beams from four discrete waveguide input ports to a common output port. By coupling each wavelength into the fundamental mode of the waveguide circuit, common boresight of the combined wavelengths was achieved. Precision CNC milling techniques have been used to manufacture the hollow waveguide circuit and the alignment slots for the dichroic components, in a common Macor substrate. 4.2 W of combined output power from three quantum cascade lasers (QCLs) and a thulium fibre laser pumped Ho:YAG laser was demonstrated, with an overall transmission for the hollow waveguide beam combiner (HWBC) optical circuit of 93%. Propagation losses in the waveguide sections were negligible. The major contributor to the overall loss was the performance of the dichroic optics for the near diffraction-limited beams used here. The four wavelengths were co-boresighted to better than 20 µrad in the common output beam exiting the HWBC optical circuit. The performance of the HWBC optical circuit was measured to be insensitive to lateral and angular misalignments typical for operation over a wide temperature range.

9726-3, Session 1

High peak power ultrafast Cr:ZnSe oscillator and power amplifier Evgeny Slobodchikov, IPG Photonics Corp. (United States); Logan R. Chieffo, Kevin F. Wall, Q-Peak, Inc. (United States) Q-Peak Inc. has developed a Cr:ZnSe based femtosecond oscillator – power amplifier laser operating in the 2.5 ?m region. The system generates 1 mJ per pulse at a 1-kHz repetition rate with a pulse duration of 184 fs, corresponding to a peak power of 5 GW. To the best of our knowledge this represents a record power for this spectral region. The high-peak power source utilizes a hybrid laser architecture, combining efficient fiber-laser pumping of solid state crystals. A Tm:fiber laser pumped, SEASAMinitiated, Cr:ZnSe femtosecond oscillator provides a seed for chirped pulse amplification. 50-fs pulses from the oscillator are stretched in a grating pulse stretcher and then amplified in a chain consisting of a regenerative amplifier and two stages of linear amplifiers all based on Cr:ZnSe. The pump power for the amplification is provided by a Q-switched, high repetition rate, Ho:YLF laser, which in turn, is pumped by a high power Tm:fiber laser. The amplified pulses are compressed by a grating pulse compressor, resulting in 1 W of average power at a 1-kHz repetition rate. This laser system represents the state-of-the-art in short-pulse duration, pulse energy, and beam quality in this IR spectral range.

9726-4, Session 1

9726-2, Session 1

High brightness diode pumped Er:YAG laser system at 2.94 µm with nearly 1kW peak power Manuel Messner, Arne Heinrich, Clemens Hagen, Pantec Engineering AG (Liechtenstein); Karl Unterrainer, Technische Univ. Wien (Austria) Over the last two decades, the need for diode pumped solid state (DPSS) lasers has increased drastically due to their obvious advantages of mainly stability and ruggedness, compared to conventional flash-lamp systems. Of special interest is Er:YAG as a crystal material since light at 2.94µm is emitted, coinciding with a major water absorption line. This allows the presented laser system to efficiently cut hard and soft biological tissue for future medical applications, and, furthermore, industrial applications like glass cutting are now within reach. We demonstrated a monolithic high-power DPSS Er:YAG laser at 2.94µm with average output power of up to 50W and pulse energy beyond 300mJ in 300µs pulses. The high peak power of nearly 1kW is delivered in a high quality beam (M?15 mJ pulses at repetition rates over 150 Hz. The design leverages an end-pumped solid-state laser geometry to produce better eyesafe beam quality ( 100 mJ at laser repetition rates of > 100 Hz.

9726-18, Session 4

Narrow linewidth UV laser transmitter for ozone dial remote sensing application Ti Chuang, Joe Hansell, Tim Shuman, Tom Schum, Kent Puffenberger, Ralph Burnham, Fibertek, Inc. (United States) Fibertek has demonstrated a dual-wavelength narrow linewidth UV laser source for NASA airborne ozone DIAL remote sensing application (Global Ozone Lidar Demonstrator). The application requires two narrow linewidth lasers in the UV region between 300 nm and 320 nm with at least 12 nm separation between the two wavelengths. Each UV laser was based on a novel ring structure incorporating an optical parametric oscillator (OPO) and a sum frequency generator (SFG). The fundamental pump source of the UV laser was a single frequency 532 nm laser, which was frequencydoubled from a diode-pumped, injection-seeded single frequency Nd:YAG laser operating at 1064 nm and 50 Hz repetition rate. The ring frequency converters generated UV wavelengths at 304 nm and 316 nm respectively. The demonstrated output energies were 2.6 mJ for 304 nm and 2.3 mJ for 316 nm UV lines, with rooms to potentially achieve more energy for each laser. Linewidth narrowing was achieved using a volume Bragg grating as the output coupler of the OPO in each ring oscillator. We obtained spectral linewidths (FWHM) of 0.12 nm for the 304 nm line and 0.1 nm for the 316 nm line. Fibertek is now building an airborne DIAL transmitter based on the reported demonstration, which is a single optical module with dualwavelength output at the demonstrated wavelengths. NASA plans to field the DIAL transmitter as a key component of the Global Ozone Lidar Demonstrator high altitude airborne instrument to perform autonomous global ozone DIAL remote sensing field campaigns.

9726-19, Session 4

Diode-pumped alexandrite ring laser for lidar applications Alexander Munk, Bernd Jungbluth, Michael Strotkamp, Hans-Dieter Hoffmann, Reinhart Poprawe, FraunhoferInstitut für Lasertechnik (Germany); Josef Höffner, LeibnizInstitut für Atmosphärenphysik e.V. (Germany) In recent years scientific climate investigations have gained increasing importance. To validate numerical simulations of the Earth’s climate, temperature distributions in the atmosphere at altitudes between 80 and 110 km have to be investigated. Lidarsystems based on flashlamppumped Alexandrite ring lasers in single frequency operation represent

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9726: Solid State Lasers XXV: Technology and Devices a powerful source for these investigations but provide low efficiency and high maintenance effort. To overcome these drawbacks diode-pumped Alexandrite lasers are required. The 7 mm-long Alexandrite crystal was longitudinally pumped by a commercial diode bar module in the red spectral region and the resulting thermal lens was investigated at different operating points. A linear resonator was designed for operation in quasi-cw mode at 35 Hz and yielded to 4 mJ pulse burst energy at 770 nm with an optical efficiency of 21%. The wavelength could be tuned via temperature tuning of the Alexandrite crystal. In Q-switched operation 0.8 mJ pulse energy were demonstrated at 770 nm and 35 Hz with a pulse duration of 300 ns. Based on the results of the linear cavity a diode-pumped Alexandrite ring laser was realized. Two diode modules were used to longitudinally pump two Alexandrite crystals which were implemented in one oscillator. The ring laser was operated at 100 Hz in quasi-cw operation and 6.2 mJ pulse burst energy could be demonstrated at 770 nm. The resulting optical efficiency was 15%. Further experiments should demonstrate Q-switched, unidirectional and single frequency operation of the Alexandrite ring laser. Power scaling can be carried out by subsequent amplification.

9726-20, Session 4

Laser transmitter design and performance for the slope imaging multi-polarization photon-counting lidar (SIMPL) instrument Anthony W. Yu, David J. Harding, Philip W. Dabney, NASA Goddard Space Flight Ctr. (United States) The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) instrument is a polarimetric, two-color, multi-beam push broom laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program and has been flown successfully on multiple airborne platforms since 2008. The SIMPL transmitter is based on a high repetition rate (~12 kHz), short-pulse (~1 ns), linearly-polarized microchip laser centered at 1064 nm. Part of the near infrared (NIR) beam at 1064 nm is frequency doubled to 532 nm (Green). Each of the NIR and Green beams is split into four push-broom beams. The output of the SIMPL instrument has 4 linearly-polarized beams each with co-aligned wavelengths in order to have co-incident NIR and Green footprints at the surface. A KTP crystal is used for the frequency doubling with temperature control used to vary conversion efficiency between 37% and 6% in order to equalize the signal strength of the two wavelengths as a function of surface type. A dichroic filter is used to separate the two colors into individual beam paths. In each of the beam paths, two tandem calcite crystals with different lengths and waveplates are used to separate the single input beam into four equally spaced beams. An array of half waveplates are used after the last calcite crystal to correct the alternating polarization of the four output beams so they have the same state of polarization (SOP). The NIR and Green beams are then recombined so they are co-aligned with the same SOP before entering a lens array for beam shaping and divergence control. A recent addition for this laser transmitter is a transmit echo pulse (TEP) feature for each color to quantify the pulse shape and amplitude for use in correcting received signal range biases. A receiver dichroic divides the two wavelengths into separate paths which are further divided using polarizing beam splitting cubes into signals parallel and perpendicular to the transmit beam. Sixteen single-photon counting modules (SPCM) and timing electronics with 0.1 nsec precision are used to determine range to the target for the four color/polarization states on the four beams. The short pulse width and high timing precision achieves an 8 cm range precision per single detected photon. Upon aggregation of the signal photons into a range histogram a measurement with a few cm resolution of pulse broadening is achieved. The broadening is due to surface slope and roughness within the footprint and light transmission into the target resulting in volume scattering. In this talk we will discuss the laser transmitter performance and present recent science data collected over the Greenland ice sheet and sea ice in support of the NASA Ice Cloud and land Elevation Satellite 2 (ICESat-2) mission to be launched in 2017.

Return to Contents

9726-21, Session 4

A single-frequency double-pulse Ho:YLF laser for CO2-lidar Philipp Kucirek, Ansgar Meissner, Patrick Eiselt, Marco Höfer, Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany) For measuring trace-gas abundances with the differential absorption lidar technique a pair of single-frequency laser pulses with highly stable emission wavelengths adjusted to the specific trace-gas of interest is required. In order to reduce mass and volume requirements for the laser beam source for a prospective space-borne system it is advantageous if the required pair of laser pulses is generated in only one optical assembly. For CO2 a detection wavelength of 2051 nm can be used, but the requirements on spectral stability are very challenging. A q-switched Ho:YLF laser oscillator with a bow-tie ring resonator, specifically designed for high-spectral stability, is reported. It is pumped with gain-switched pulses from a Tm:YLF laser at 1.9 µm. The ramp-and-fire method with a DFB-diode laser as a reference is employed for generating single-frequency emission. With a repetition rate of 50 Hz, pulse pairs with a temporal separation of 750 µs are produced. The measured pulse energy is 2 mJ and the measured pulse duration is 15 ns for each of the two pulses in the burst. The standard deviation of the emission wavelength of the laser pulses of 2051 nm is measured with the heterodyne technique to be below 1.5 MHz over 2 seconds of integration time. Future work will be in further increasing the spectral stability of the laser pulses and in building up an INNOSLAB pulse amplifier for pulse energy scaling towards 40 mJ (online pulse) and 15 mJ (offline pulse).

9726-22, Session 4

Post-flight test results of diode laser bar subjected to space exposure Narasimha S. Prasad, NASA Langley Research Ctr. (United States) This paper discusses the recently completed post-flight test results of a G-Stack diode laser unit that was sent on NASA’s MISSE 7 mission. The 5 bar G stack operating around 808 nm with 1 kW survived the harsh space environment with some reduction in performance due to contamination. The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months. MISSE missions provided an opportunity for developing space qualifiable materials. This laser stack was a part of lidar component package on the MISSE 7 box that was transported to the international space station (ISS) via STS 129 and returned to the Earth via STS 134. The STS 129 mission was launched on Nov 16, 2009 and the MISSE 7 package was brought back to the earth via the STS 134 that landed on June 1, 2011. This package that was in space environment for more than one and a half year included fiber laser, solid-state laser gain materials, coherent receiver, and semiconductor laser diode. The post-flight testing of several MISSE 7 materials that were recently returned back after more than one year of exposure on the International Space Station (ISS) is underway. This paper will present the comparison of pre-flight and post-flight performance characteristics and discuss the effect of space exposure as well as contamination on the diode laser stack.

9726-53, Session 4

Demonstration of a 500 mJ InnoSlabamplifier for future lidar applications Jens Löhring, Michael Strotkamp, Florian Elsen, Raphael Kasemann, Jürgen Klein, Martin Traub, Gerd Kochem,

+1 360 676 3290 · [email protected]

7

Conference 9726: Solid State Lasers XXV: Technology and Devices Ansgar Meisssner, Marco Höfer, Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany) In the field of atmospheric research lidar is a powerful technology to measure remotely different parameters like gas or aerosol concentrations, wind speed or temperature profiles. For global coverage spaceborne systems are advantageous. To achieve highly accurate measurements over long distances high pulse energies are required. A Nd:YAG-MOPA system consisting of a stable oscillator and two subsequent InnoSlab-based amplifier stages was designed and built as a breadboard demonstrator. Overall, more than 500 mJ of pulse energy at 100 Hz pulse repetition frequency at about 30 ns pulse duration in single longitudinal mode was demonstrated. Being seeded with 75 mJ pulses, the 2nd amplifier stage achieved an optical efficiency (pump energy to extracted energy) of more than 23% at excellent beam quality. Recently, different MOPA systems comprising a single InnoSlab amplifier stage in the 100 mJ regime were designed and built for current and future airborne and spaceborne lidar missions. Amplification factors of about 10 at optical efficiencies of about 23% were achieved. In order to address the 500 mJ regime the established InnoSlab design was scaled geometrically in a straight forward way. Hereby, the basic design properties like stored energy densities, fluences and thermal load densities could be retained. The InnoSlab concept has demonstrated the potential to fulfill the strong requirements of spaceborne instruments concerning high efficiency at low optical loads, excellent beam quality at low system complexity. Therefore, it was chosen as baseline concept for the MERLIN mission, currently in phase B.

9726-23, Session 5

100-J UV laser for dynamic compression research Jason S. Zweiback, Logos Technologies, Inc. (United States); Scott Fochs, Univ. of Rochester (United States); Jake Bromage, Douglas Broege, Robert Cuffney, Laboratory for Laser Energetics, University of Rochester (United States); Zachary Currier, Logos Technologies Inc (United States); Christopher Dorrer, Laboratory for Laser Energetics, University of Rochester (United States); Brian Ehrich, Univ. of Rochester (United States); Jim Engler, Logos Technologies Inc (United States); Mark Guardalben, Laboratory for Laser Energetics, University of Rochester (United States); Nick Kephalos, Logos Technologies Inc (United States); John Marozas, Richard Roides, Laboratory for Laser Energetics, University of Rochester (United States); Jon Zuegel, Univ. of Rochester (United States) A 100 J, 351 nm laser is under construction for the Dynamic Compression Sector located at the Advanced Photon Source. This laser will drive shocks in solid-state materials which will be probed by picosecond x-ray pulses available from the synchrotron source. Using proven technology, the laser is designed for reliability and ease of use. A state-of-the-art fiber front end provides pulse lengths up to 20 ns with pulse shapes tailored to optimize shock trajectories. A diode-pumped Nd:glass regenerative amplifier is followed by a four-pass, flash-lamp-pumped rod amplifier. The regenerative amplifier is designed to produce up to 20 mJ with high stability. The final amplifier uses a six-pass 15-cm Nd:glass disk amplifier based on an OMEGA laser design. A KDP Type-II/Type-II frequency tripler configuration converts the 1053-nm laser output to a wavelength of 351 nm and the ultraviolet beam is image relayed to the target chamber. Smoothing by spectral dispersion and polarization smoothing have been optimized to produce uniform shocks in the materials to be tested. Modeling shows that better than 6% RMS uniformity should be achieved in a 500 mm diameter (FWHM) far-field spot. Custom control software collects all diagnostic information and provides a central control for all aspects of laser operation. We will

8

discuss the overall design of the laser system, the current status, and further applications of this laser.

9726-24, Session 5

Megawatt-level peak-power from a passively Q-switched hybrid fiber-bulk amplifier and its applications Axel Reiser, Juraj Bdzoch, Sven Höfer, Sina Riecke, Daniel Seitz, Nicolas Kugler, Peter Genter, ROFIN-SINAR Laser GmbH (Germany) A novel laser system with optical parameters that fill the gap between Q-switched and modelocked lasers has been developed. It consists of a high gain hybrid fiber-bulk amplifier seeded by a low power SESAM Q-switched oscillator. The mW level output power of the seed oscillator is preamplified by a single mode fiber which is limited by SRS effects. The final amplification stage is realized by two, longitudinal pumped, Nd:YVO4 crystals in a double pass setup. This MOPA configuration delivers sub-300ps pulses at repetition rates up to 1 MHz with an output power exceeding 60 Watt. Nonlinear frequency conversion to 532nm and 355nm is achieved with efficiencies of >75% and >45%, respectively. Due to the high peak power, high repetition rate and high beam quality of this system, applications formerly only addressable at lower pulse repetition frequencies or with complex modelocked laser systems are now possible with high speed and lower cost of ownership. Application results that take benefit of these new laser parameters will be shown. Furthermore, the reduction of the pulse duration to sub-100ps and power scaling to output powers >100 Watt by the use of the Innoslab concept are being presented.

9726-25, Session 5

High energy pulsewidth tunable CPA free picosecond source Julien Pouysegur, Florent Guichard, Institut d’Optique Graduate School (France); Yoann Zaouter, Amplitude Systèmes (France); Marc Hanna, Frédéric Druon, Institut d’Optique Graduate School (France); Clemens Hönninger, Eric Mottay, Amplitude Systèmes (France); Patrick Georges, Institut d’Optique Graduate School (France) Work on a Fourier transform limited picosecond source composed of a seeder system tunable in pulse duration and a hybrid fiber – bulk amplifier able to provide large gain, high pulse energy, and high average power is presented. Spectral compression effect induced by self-phase modulation (SPM) in an optical fiber is exploited to obtain the pulsewidth tunability. To increase pulse energy beyond self-focusing threshold both in the fiber amplifier and Yb:YAG amplifier, Divided Pulse Amplification architecture is investigated. This had led to a source able to delivering 3ps 350µJ pulses at 50 kHz of repetition rate, corresponding to an average power of 17.5W. These performances are obtained in a compact and robust in a CPA free setup, and can be easily adjusted in a large range of pulsewidth (3 – 20 ps), energy (10 – 350 µJ), and average power (10 – 50 W), making it a particularly versatile source. A maximum pulse energy of 720µJ has been demonstrated with 20ps pulse duration without any use of divided pulse scheme, corresponding to a peak power of 36MW per pulse. 116MW peak power has been made by reducing the pulse duration down to 3ps together with employment of divided pulse scheme generating 4 temporal replicas. This hybrid configuration is well useful to improve by a factor of one hundred the output peak power of fiber systems available.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9726: Solid State Lasers XXV: Technology and Devices

9726-26, Session 5

Multi-joule lasers operating at 60+ Hz for industrial and scientific applications Ryan Feeler, Chris Briggs, Wade Collins, Jay Doster, Faming Xu, Northrop Grumman Cutting Edge Optronics (United States) A new generation of diode-pumped solid-state lasers has been developed that enables operation at high energies (1-10 J/pulse) and high repetition rates (tens to hundreds of Hz). Data for two separate lasers operating at 60Hz is presented – one a 1.2J, 532nm laser and the other a 1.5J, 1064nm, single longitudinal mode (SLM) laser. Data for a 10J, 1053nm, 20Hz, SLM system is also presented. The impact of wavelength seeding and oscillator design on the final output parameter of the laser is discussed. A discussion of the suitability of these lasers in their applications (Raman spectroscopy, material inspection, and laser peening) is also discussed. Special attention is paid to the design of the relay imaging system in these lasers, in order to generate the flat-top output beams that are required by these applications. Design details are presented and the path to higher pulse energies and repetition rates is discussed. Life test data for the pump diodes is also presented, demonstrating an expected operating lifetime in excess of 10 billion pulses before replacement diodes are required.

9726-27, Session 5

A compact solid state laser Bhabana Pati, Eric D. Park, Kenneth Stebbins, Q-Peak, Inc. (United States) Compact, lightweight, and efficient lasers are essential for space based and unmanned aerial vehicle (UAV) applications where there are constraints on size weight and power (SWaP). We have developed a compact, passively Q-switched, intra-cavity frequency doubled Nd:YLF laser that produces 1-mJ of energy in a 10-ns pulse at a 1-30 Hz repetition rate. In order to obtain a high energy per pulse at repetition rates ~ 30 Hz, we chose Nd:YLF as the laser material as it has a longer upper state lifetime compared with the more common material, Nd:YAG. The laser is side-pumped by a semiconductor laser and passively Q-switched by a saturable absorber. A KTP crystal is placed inside the laser resonator to double the laser frequency to generate green light at 523 nm. The resonator was optimized to obtain near diffraction limited beam. The overall volume of the laser head is < 8 cm3 and the weight is < 80 gm. The unique pumping geometry makes the laser power insensitive to the temperature over +/- 5 °C. The laser head is designed to be insensitive to mechanical or thermal misalignment.

9726-28, Session 5

High energetic and highly stable pulses from a Ho:YLF regenerative amplifier Peter Kroetz, Max-Planck-Institut für Struktur und Dynamik der Materie (Germany) and Deutsches Elektronen-Synchrotron (Germany); Axel Ruehl, Deutsches Elektronen-Synchrotron (Germany); Anne-Laure Calendron, Huseyin Cankaya, Deutsches ElektronenSynchrotron (Germany) and Ctr. for Free-Electron Laser Science (Germany) and The Hamburg Ctr. for Ultrafast Imaging (Germany); Krishna Murari, Deutsches ElektronenSynchrotron (Germany) and The Hamburg Ctr. for Ultrafast Imaging (Germany) and Univ. Hamburg (Germany); Gourab Chatterjee, Max-Planck-Institut für Struktur und Dynamik der Materie (Germany) and Ctr. for Free-Electron

Return to Contents

Laser Science (Germany); Franz X. Kärtner, Deutsches Elektronen-Synchrotron (Germany) and The Hamburg Ctr. for Ultrafast Imaging (Germany) and Ctr. for Free-Electron Laser Science (Germany); Ingmar Hartl, Deutsches Elektronen-Synchrotron (Germany); R. J. Dwayne Miller, Max-Planck-Institut für Struktur und Dynamik der Materie (Germany) and Ctr. for Free-Electron Laser Science (Germany) and The Hamburg Ctr. for Ultrafast Imaging (Germany) We present, to the best of our knowledge, record high output pulse energies from Ho:YLF regenerative amplifier (RA) seeded by a Ho:Fiber oscillator. The system delivers pulse energies of above 10 mJ at 100 Hz and above 4 mJ at 1 kHz, with less than 1.5 % rms fluctuation. The output spectrum of the pulses supports a Fourier limited duration of 2.8 ps. This laser system is ideally suited for ultrafast Mid-IR OPCPAs, high energy THz generation and strong-field experiments. Due to the high energy storage capacity and long upper state life time of Ho:YLF, Ho:YLF RAs are highly susceptible to show pulse instability, in the form of bi- and multifurcation, when seeded with low energy seed pulses. We show both theoretically and experimentally that apart from a first operation region, a second operation point exists at a larger round trip number exhibiting almost one order of magnitude less pulse fluctuations. This operation point is, to the best of our knowledge, demonstrated experimentally for the first time. The experimental results are supported by simulations that reveal this system behavior under the conditions of a high gain build-up and high gain depletion for consecutive pump and amplification cycles. Here, the effects of seed and pump noise are negligible or significantly suppressed, respectively. Operation at high pump powers and high pulse energies require a careful system design. We will also discuss general design guidelines for operation at the second stability point to suppress pulse instabilities without sacrificing high pulse energy.

9726-29, Session 6

High-gain, high-energy picosecond Nd:YVO4 amplifier end-pumped at 880 nm Xavier Delen, Institut d’Optique Graduate School (France); Loic Deyra, ALPhANOV (France) and Spark Lasers (France); Simon Salort, ALPhANOV (France); Pascal Dupriez, ALPhANOV (France) and Spark Lasers (France); François Balembois, Patrick Georges, Institut d’Optique Graduate School (France) We demonstrate a high-gain, high-energy bulk amplifier in picosecond regime. The seed laser system is carefully optimized in order to obtained a central wavelength at 1064.3 nm and a spectral linewidth of 0.33 nm ideally matching the main emission line of Nd:YVO4. The fiber-based seed laser emits pulses with an energy of 5 nJ at repetition rates ranging from 1 kHz to 10 MHz and a pulse duration of 7 ps. The gain medium is a 20 mm long 0.2 at. % doped Nd:YVO4 crystal longitudinally pumped with a highbrightness, VBG locked 60 W fiber coupled laser diode emitting at 880 nm. The amplifier is operated in a double pass configuration using a Faraday rotator to extract the signal beam after the second pass. Different pumping schemes are compared experimentally showing that two sides pumping results in higher output power than one side pumping. The output power of the amplifier ranges from 14.4 W to 25.5 W for seed powers between 20 µW to 56 mW. For a repetition rate of 200 kHz, the output energy reaches up to 93 µJ with a pulse duration of 8 ps which gives a peak power of 11 MW. It corresponds to an output power of 18.6 W and a gain of 42 dB. The influence of the pumping scheme on the peak power limitation due to selfphase modulation is also studied. This source is well suited to meet specific requirements of micro-machining applications.

+1 360 676 3290 · [email protected]

9

Conference 9726: Solid State Lasers XXV: Technology and Devices

9726-30, Session 6

VCSEL-pumped passively Q-switched monolithic solid-state lasers Robert van Leeuwen, Bing Xu, Tong Chen, Qing Wang, Jean-Francois Seurin, Princeton Optronics, Inc. (United States); Guoyang Xu, Delai Zhou, Princeton Optronics Inc (United States); Chuni L. Ghosh, Princeton Optronics, Inc. (United States) Compact, low-cost, Q-switched diode-pumped solid-state lasers (DPPS) with high pulse energy are needed for many applications, such as laser range finders, laser designators, laser breakdown spectroscopy, and laser ignition. In many of those applications the lasers need to operate at high temperatures where typical edge-emitting laser diode pump lasers show poor reliability. Recently, high power vertical-cavity surface-emitting laser (VCSEL) arrays have been demonstrated as excellent pump sources for diode-pumped solid-state lasers. Their key advantages over the existing edge-emitter technology include simpler coupling optics, reduced wavelength sensitivity to temperature, and increased reliability, especially at high temperatures, low-cost manufacturing, and two-dimensional planar scalability. These features make VCSEL technology very well suited for constructing low-cost DPSS lasers with high pulse energy. Here we report on a very compact VCSEL end-pumped, passively Q-switched Nd:YAG laser with high pulse energy. The laser only comprises 3 components: a high power VCSEL pump module, an aspheric condenser lens as a pump optic, and a diffusion bonded composite laser rod consisting of an Nd:YAG gain medium and a Cr:YAG saturable absorber. The laser rods are coated with high damage threshold dielectric coatings on each end to form the laser end mirrors. A thermal lens stabilizes the laser cavity. The laser pulse energy, q-switch delay time, and optical efficiency of the passively Q-switched monolithic solid state lasers were measured as a function of VCSEL power for various rod lengths, Cr doping levels, and VCSEL heatsink temperatures. Up to 23.6 mJ laser pulse energy was achieved with 11.9% optical efficiency.

9726-31, Session 6

Simple ps microchip Nd:YVO4 laser with 3.3 ps pulses at 0.2 - 1.4 MHz and singlestage amplification to the microjoule level Erdal Türkyilmaz, MONTFORT Laser GmbH (Austria); Christian Guenther, Eva Mehner, Technische Hochschule Nürnberg Georg Simon Ohm (Germany); Daniel Kopf, MONTFORT Laser GmbH (Austria); Harald Giessen, Univ. Stuttgart (Germany); Bernd Braun, Technische Hochschule Nürnberg Georg Simon Ohm (Germany) Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 to 2 MHz, and micro Joule level pulse energies. Many systems are based on short pulse modelocked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50 µm long Nd:YVO4-gain material optically bonded to a thick undoped YVO4-crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 - 1.4 MHz at a wavelength of 1.064 µm. The pulse energy is a few nJ. These 40-ps pulses are spectrally broadened in a standard single mode fiber and then compressed in a 24mm long CBG (chirped Bragg grating) to as low as 3.3 ps. The repetition rate can be tuned from app. 0.2 to 1.4 MHz by changing the pump power while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fiber is observed throughout the pulse repetition rate, supporting sub-10-ps pulses. Finally, the pulses are amplified in a single-

10

stage Nd:YVO4 -amplifier up to the microjoule level ( up to >2 µJ pulse energy). We have demonstrated a simple laser system which generates µJ-level, sub-10-ps pulses with a repetition rate tuneable from 0.2 to 1.4 MHz without active switching components and which can be integrated in a very compact setup.

9726-32, Session 6

Efficient broadband TW level OPCPA pumped by a rectangular pulse Yuriy Stepanenko, Pawel Wnuk, Tomasz Kardas, Michal Nejbauer, Czeslaw Radzewicz, Univ. of Warsaw (Poland) Currently, there are two viable routes towards high peak-power laser systems. A traditional one relies on laser amplifiers in some variation of the Chirped Pulse Amplification (CPA) scheme. Its major limitation comes from the thermal effects in the amplifying medium severely limiting the repetition rate laser systems. An alternative approach uses optical parametric amplification in a nonlinear crystal to transfer the energy directly from the pump beam to the amplified ultrashort pulse beam. We will present the results on a table top multi-TW ns-pumped OPCPA system with time shear. The results of theoretical considerations show that, with proper design, the system can potentially achieve extremely high efficiency as well as good temporal and spatial characteristics of the pulses. The possibility of usage of alternative, biaxial crystals (KTP, BiBO) with the pump and signal beams not necessary propagating within the major crystal planes will be discussed. We will demonstrate experimental results of a system consisting of a femtosecond oscillator followed by a stretcher and a two-stage optical parametric amplifier. The amplifier is pumped with 532nm beam with a rectangular temporal pulse shape of 4 ns duration. The three-pass preamplifier boosts the nJ seed pulse energy by a factor of approximately 106. The power amplifier uses three BBO crystals enhancing the efficiency of the system to 35%. The spectrum of the output pulses is broad enough to support 15 fs pulse duration. This, together with hundreds of mJ of the output pulse energy shows that the system is capable of multi-TW operation.

9726-33, Session 7

High repetition rate (100 Hz), high peak power, high contrast femtosecond laser chain Raphael Clady, Vadim I. Tcheremiskine, Yasmina Azamoum, Laurent Charmasson, Nicolas Sanner, Olivier P. Uteza, Marc L. Sentis, Lasers, Plasmas et Procédés Photoniques (France) High intensity femtosecond laser are now routinely used to produce energetic particles and photons via interaction with solid targets. However, the relatively low conversion efficiency of such processes requires the use of high repetition rate laser to increase the average power of the laser-induced secondary source. Furthermore, for high intensity laser-matter interaction, a high temporal contrast is of primary importance as the presence of an ASE (Amplified Spontaneous Emission) pedestal and/or various prepulses may significantly affect the governing interaction processes by creating a preplasma on the target surface. We present the characterization of a laser chain based on Ti:Sa technology and CPA technique, which presents unique laser characteristics in the world: a high repetition rate (100 Hz), a high peak power (10 TW) and a high contrast ratio (ASE 65% and 18% conversion efficiency, respectively. Upgrade of the regen to 5mJ will be demonstrated soon. The cavity of the upgrade amplifier has already been tested in CW regime with 560W output power and no sign of roll over. Results of the seeded operation, efficiency of pulse compression at 0.5kW by a CVBG, and results of improved conversion to 2nd and 4th harmonics will be presented. Other beamline which is being developed is a double stage 1kHz beamline with 0.5J expected energy in a picosecond pulse. The first stage, a QCW-pumped Yb:YAG regenerative amplifier, is now used in application experiments with 45mJ pulse energy after compression by a grating-based compressor. Pulse length is 99.9%. They are an attractive alternative to traditional thin film anti-reflection (AR) coatings for several reasons: They provide AR performance over a larger spectral and angular range; and unlike thin film coatings, they are patterned directly into the optic rather than deposited on its surface. As a result, they are not prone to delamination under thermal cycling that can occur with thin film coatings, and their laser damage thresholds can be considerably higher. In this work, an optimized reactive ion etch procedure was used to pattern rARSSs on fused silica windows, with performance optimized for high energy laser (HEL) applications at 1.06 µm. We have demonstrated scale up of this processing technique for windows up to 12” in size. This work represents what we believe to be the largest diameter nanostructured surface on an inorganic material. The windows have been shown to have a laser damage thresholds at 1.06 µm of >100 J/cm2 – approaching those of the substrate, and approximately five times higher than those of comparable, high quality thin film AR coatings. We present results for the AR properties and uniformity of these large windows.

9726-55, Session 11

Spectral and temporal control of Q-switched solid-state lasers using intracavity MEMS

The integration of micro-electro-mechanical systems (MEMS) into solid-state laser systems enables extra functionalities for temporal, spectral or spatial tuning of laser characteristics, while simultaneously offering miniaturised, low-cost alternatives to conventional bulk optics used in solid-state lasers. We will present results showing the Q-switch temporal characteristics of a novel Nd:YAG laser system incorporating two intracavity MEMS micromirrors. This new arrangement extends the functionality of single micromirror based Q-switched solid-state lasers that we, and other research groups, have previously reported. The micromirrors used in our dualmicromirror cavity configuration have different actuation mechanisms: one is electrostatically-controlled for fast resonant scanning at 10 kHz; the other is electrothermally-controlled for slower resonant scanning at 2 kHz or quasi-static displacement. This dual-micromirror technique enables the “fast scan” mirror to control the Q-switch pulse duration. Pulse durations ranging from 30 ns (cavity-limited) up to multiple microseconds can be achieved, with average output powers exceeding 50 mW. Further functionalities, such as pulse burst control or pulse-on-demand control, are achievable through simultaneous actuation of the “slow scan” micromirror. MEMS can also allow spectral control of solid-state laser outputs. Using an intracavity micromirror and a prism or diffraction grating, the output wavelength of a Yb:KGW laser platform can be tuned by controlling the angular position of the micromirror. We will present initial results on the spectral tuning characteristics, and discuss combining spectral and temporal control using MEMS micromirrors. This combined control could provide avenues for a miniaturised, flexible laser system impacting defence and industrial applications.

9726-56, Session 11

Compact single-frequency polarization maintaining CW single stage fiber amplifier Enkeleda Balliu, Magnus Engholm, Mid Sweden Univ. (Sweden); Lars Norin, Acreo FiberLab (Sweden); Gunnar Elgcrona, Jonas Hellström, Håkan Karlsson, Cobolt AB (Sweden) Our objective in this work is to demonstrate a highly compact, singlefrequency, polarization maintaining CW laser system (MOPA) at 1064nm (and 532/355 nm by frequency conversion). Our motivation is to reduce the complexity (and cost) of the overall laser system by using only one amplification stage and a few optical components. The overall system is based on a hybrid solid state laser (SSL)/fiber amplifier where a key component is a compact ring-cavity Nd:YAG solid state laser (SSL) operating in single frequency (10 kHz linewidth), with an ultra-low noise and an excellent beam quality. In the present configuration the SSL provides up to 500mW and with a PER of > 30dB but can be designed for power levels up to 3W. The single stage fiber amplifier is constructed by using PM fiber optic components with relatively small core/cladding dimensions of 10/125 um. A short (less than 2 m), custom made, highly Yb-doped fiber (pump absorption >3 dB/m at 920nm) with high photodarkening resistance is used, allowing for reduced non-linear effects (Stimulated Brillouin Scattering). In the present configuration, a (2+1)x1 PM combiner and two pump LD’s at 976nm (25W) provides SBS free output power levels up to 30W at 1064nm with a PER of more than 20dB. A custom made, anti-reflective coated fused silica endcap (2 x 4mm) is spliced to end of the active fiber. Single-pass, extra-cavity frequency conversion to 532nm (and 355nm) is demonstrated by using different non-linear crystals (LBO, KTP and PPKTP) with conversion efficiencies up to 40%.

Alan Paterson, Ralf Bauer, Ran Li, Univ. of Strathclyde (United Kingdom); Caspar Clark, Helia Photonics Ltd. (United Kingdom); Walter Lubeigt, Deepak Uttamchandani, Univ. of Strathclyde (United Kingdom)

Return to Contents

+1 360 676 3290 · [email protected]

19

Conference 9726: Solid State Lasers XXV: Technology and Devices

9726-57, Session 11

9726-59, Session 11

High brightness sub-nanosecond Q-switched laser using volume Bragg gratings

Tunability of the highly stable singlefrequency mode of a hybrid laser

Brian M. Anderson, Evan Hale, George Venus, Daniel Ott, Ivan Divliansky, Leonid Glebov, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States) The design of Q-switched lasers capable of producing pulse widths of 100’s of picoseconds necessitates the cavity length be shorter than a few centimeters. Increasing the amount of energy extracted per pulse requires increasing the mode area of the resonator that for the same cavity length causes exciting higher order transverse modes and decreasing the brightness of the output radiation. To suppress the higher order modes of these multimode resonators while maintaining the compact cavity requires the use of intra-cavity angular filters. A novel Q-switched laser design is presented using volume transmitting Bragg gratings (TBGs) as angular filters to suppress the higher order transverse modes. The laser consists of a 5 mm thick slab of Nd:YAG, a 3 mm thick slab of Cr:YAG with a 20% transmission, two orthogonally aligned TBGs to suppress the higher order modes, and a 40% output coupler. The gratings are recorded in photo-thermo-refractive (PTR) glass, which has a high damage threshold that can withstand both the high peak powers and high average powers present within the resonator. The TBGs recorded in PTR glass have narrow angular selectivity ranging from 0.1 to 10 mrad, and can spatially filter beams with a diameter ranging from 0.1 to 10 mm. Experimental results are presented demonstrating the Q-switched laser with a cavity length of 1.5 cm, millijoule level output, sub-nanosecond pulse width, and diffraction limited beam quality.

9726-58, Session 11

Solid-state lasers directly pumped by InGaN diode lasers: Ti:sapphire and Pr3+:LiYF4 lasers Hiroki Tanaka, Ryosuke Kariyama, Kodai Iijima, Ryota Sawada, Fumihiko Kannari, Keio Univ. (Japan) We report our recent progress of solid-state lasers directly pumped by InGaN diode lasers of blue and green. Diode-laser-pumped mode-locked Ti:sapphire laser and praseodymium-doped LiYF4 lasers are demonstrated. A blue and green diode lasers deliver output powers of >3.5 W and >1 W. We applied these diode lasers to a Ti:sapphire laser which have been pumped by a frequency-doubled neodymium-doped lasers, and a modelocked Ti:sapphire laser is successfully demonstrated. We confirmed that the green-diode-laser pumping is advantageous compared with blue-diodelaser pumping not only due to the higher Stokes efficiency but also the lack of additional absorption loss which is induced by shorter wavelength pumping. The praseodymium-doped laser is one of the most successful lasers oscillating in visible region. It can be efficiently and directly pumped by the blue diode laser because it has absorption band around 440 nm. We report a CW operation at 640, 607 and 523 nm from the praseodymium doped LiYF4 laser, and slope efficiency of >40 % is achieved at 640 and 523 nm. In addition to the CW operation, we demonstrate a Q-switching of the laser at 640 and 607 nm by employing a Cr4+:YAG crystal as a saturable absorber, which have been recognized as a conventional passive Q-switching element for Nd:YAG laser. We finally report a mode-locking of the laser with a semiconductor saturable absorber mirror (SESAM) at 640 nm.

20

Mamoun Wahbeh, Raman Kashyap, Ecole Polytechnique de Montréal (Canada) A hybrid laser, based on a C-band semiconductor optical amplifier (SOA) coupled to a long fiber external cavity, is carefully engineered to operate with high spectral purity. The fiber cavity is made of a piece of PM erbium doped fiber, whose one end is sculpted into a biconic lens with an FBG directly written on the other end. The fiber lens has an asymmetric focus, designed to couple the diverging light beam from the SOA into the fiber core with high efficiency. Also, the waveguide of the SOA is tilted relative to the AR facet to suppress axial mode instabilities. Thus combining the attributes of an FBG, erbium doped fiber and semiconductor optical amplifier, a highly stable 2-kHz linewidth single external-cavity mode operating with a SMSR of > 42 dB is demonstrated. Fine tunability of this mode within a single mode-spacing is experimentally achieved. The ability to scan 218 MHz with a frequency-current coefficient of ~2.18 MHz/mA is reported. Moreover by changing temperature of the external fiber Bragg grating, a range of 1.8 GHz is smoothly scanned at a resolution of ~170 MHz and with a frequency-temperature coefficient of 3.1GHz/K. Consequently, the desired operating wavelength can be roughly set by tuning Bragg wavelength and exactly reached via the bias current. A frequency accuracy of ±11 Hz is estimated while the output power at the peak lasing wavelength is measured to be 13.3 dBm. This compact laser with such simple structure and high spectral quality is sought by many segments of industry.

9726-60, Session 11

11.5W Yb:YAG planar waveguide laser grown by pulsed laser deposition Stephen J Beecher, James A Grant-Jacob, Tina L Parsonage, Ping Hua, Jacob I Mackenzie, Dave P Shepherd, Robert W Eason, Univ of Southampton (United Kingdom) We present details on the fabrication, characterization and laser performance of a Yb:YAG planar waveguide grown by pulsed laser deposition. The 8mm long waveguide features a 15µm-thick-core of Yb:YAG grown onto a YAG substrate. In a simple oscillator formed of a mirror highly transmissive for the pump light and highly reflecting for the signal and a 50% reflectivity output coupler, both proximity coupled to opposing waveguide facets, 11.5W of output power was observed with a threshold of 3.0W and a slope efficiency of 47% with respect to absorbed pump power. The waveguide also oscillated with feedback provided from the Fresnel reflection of ~8% from one of the uncoated facets, but with a significantly higher threshold of 7W. This performance, with output coupling of 92%, highlights the potential suitability of these devices for use as compact high gain amplifiers with very large mode areas, in our case ~20,000µm2. Further improvements in performance are expected by increasing the dopant concentration from 1.4 at.% to 3.0 at.% and increasing the pump power.

9726-61, Session 11

Donut beam generation in a hybrid fiberlaser-pumped Ho:YAG laser A C Butler, P C Shardlow, R T Uren, W A Clarkson, Optoelectronics Research Centre (United Kingdom) Laguerre-Gaussian (LG0m) beams are characterised by a donut-shaped intensity profile and have a wide range of applications. One emerging application area is in the field of laser micromachining of materials where the sharper transverse intensity gradient of the ring-shaped beam profile

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9726: Solid State Lasers XXV: Technology and Devices compared to a Gaussian fundamental (TEM00) mode yields better edge definition and edge quality. In this paper we describe a power-scalable laser architecture for generating LG0m modes directly in a solid-state laser. Our approach employs a hybrid fiber-laser-pumped Ho:YAG laser, where the pump beam from a Tm fiber laser at 1908 nm is re-shaped to yield a near-field annular profile for the purpose of directly exciting the desired LG0m mode in an end-pumped Ho:YAG laser. The beam shaping element is a simple silica capillary fiber with air:silica radius ratio of 50%. The output from the capillary fiber is reimaged using an appropriate arrangement of lenses to spatially match the intensity profile of the required LG0m mode in the Ho:YAG laser to achieve preferential lasing on this mode. The combination of a low quantum defect pumping cycle and the ring-shaped pump deposition profile leads to weak thermal lensing opening up the prospect of high lasing efficiency and high output power. We report on preliminary results for direct generation of the first order (LG01) donut mode at 2.1?m and discuss a simple strategy for extending operation to higher order LG0m donut modes.

9726-62, Session 12

Frequency extension of a high power diamond Raman laser by intracavity second harmonic generation Hadiya Jasbeer, Robert Williams, Aaron McKay, Richard Mildren, Macquarie Univ. (Australia) The excellent thermal properties of diamond have recently been shown to enable frequency conversion of high-power CW beams with high efficiency and high output beam quality. To date, up to 380 W at efficiencies above 60% have been demonstrated in the infra-red. The typically high intra-cavity Stokes intensities in these lasers indicates potential for further efficient frequency conversion via second-order parametric processes as a method to generate high power and high brightness visible and UV output at wavelengths important for applications such as laser guide-stars, medical treatments and remote sensing. Here we report intra-cavity frequency doubling of an external cavity diamond Raman laser (EC-DRL) pumped using a Nd:YAG laser at 1064 nm. A lithium triborate crystal was used in a near-concentric EC-DRL to convert the intracavity 1240 nm Stokes field to 620 nm. Pumping of the EC-DRL at power up to 300 W was used with on-time durations limited to 250 micro-seconds to provide a convenient method for demonstrating high power CW conversion. The period is sufficiently long to achieve steady-state thermal gradients in the diamond, thus providing results indicative of genuine CW operation (assuming negligible heat deposition in LBO). To date, we have achieved 2.1 W (ontime power) of 620 nm with 1.4% power conversion efficiency with respect to 1064 nm pump. It is found that careful management of polarization properties of optical elements and nonlinear output coupling are crucial for increasing output power and efficiency, opening up prospects for further power scaling.

9726-63, Session 12

A 7.5-mJ, 21-ns, 7-kHz green rotary disk laser with diffraction limited beam quality Santanu Basu, Basu Labs Inc. (United States) Visible lasers with high pulse energy and high repetition rate are required for several important applications such as high-precision material processing and adaptive optics. Fiber lasers are unable to produce high pulse energy due to mode size limitation. In this paper, we will present results of a Q-switched rotary disk laser that produces 7.5 mJ pulses at 515 nm at 7 kHz repetition rate. The peak power of the green laser is 350 kW. Due to the absence of aberrations in a rotary disk laser, the beam quality is measured to be diffraction limited.

9726-64, Session 12

Compact side-pumped passively Q-switched Yb:YAG laser with frequency conversion to UV Brian Cole, Chris McIntosh, Alan D. Hays, Tom DiLazaro, Lew Goldberg, U.S. Army RDECOM CERDEC NVESD (United States) Laser sources in the UV have found utility for Raman based remote sensing applications. For this application, we have explored using a Yb:YAG passively Q-switched laser, side-pumped by a single bar diode, as a source for the fourth harmonic generation (FHG) at 257.5 nm. Side pumping of Yb:YAG with a pulsed, high peak power (100 W) laser diode bar offers a number of advantages: large pump intensities (>5kW/cm2) for efficient laser operation, a simplicity for resonator design, and compact size. The compact 30 mm long laser cavity, Q-switched by a Cr:YAG saturable absorber, was operated in a burst mode with the 5 mm pump diode pulsed for 2-4 ms at low duty cycles. Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the Cr:YAG transmission, which was varied from 70% to 85%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient FHG. Pulse energies and durations were in ranges of 1-2 mJ and 2-3ns ranges, respectively. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser. Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 20% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than 50 mW.

9726-66, Session 12

Development of high coherence high power 193nm laser Satoshi Tanaka, Masaki Arakawa, Atsushi Fuchimukai, Yoichi Sasaki, Takashi Onose, Yasuhiro Kamba, Hironori Igarashi, Chen Qu, Mitsuru Tamiya, Shinji Ito, Koji Kakizaki, Gigaphoton Inc. (Japan); Hongwen Xuan, Yohei Kobayashi, The Univ. of Tokyo (Japan); Hakaru Mizoguchi, Gigaphoton Inc. (Japan) There remains a huge frontier in laser applications because of the constraints of a light source. It is the high power DUV region, in which single photon energy matches the covalent energy levels of various carbon compounds. Considering the absorption spectrum of oxygen, 193 nm is the shortest wavelength suitable for laser processing in air. At 193 nm, however, solid state lasers are difficult to produce even 1 W output, because there is not any durable nonlinear crystal available in the short wavelength region. As a solution for this frontier, we have been developing a unique hybrid 193 nm ArF laser system which consists of a solid state laser for seeding and an ArF excimer laser for power-boosting. The high coherence quality of the solid state laser can be maintained even after the excimer boosting, enabling superior performance in the fields of interference exposure pattering, ablation process and so forth. The advantage of a solid state laser and that of an excimer compensate each other in this DUV hybrid system. The solid state laser consists of Yb and Er fiber laser systems and wavelength mixing units [1]. We have got more than 0.3 W output at 6 kHz repetition rate. By seeding the 193 nm laser light into the ArF excimer laser, we have obtained 100 W averaged power with high coherence. In this paper, we will present details of the hybrid laser system and output performance as well as some feasibility test results for various applications. [1] Hongwen Xuan et al. Optics Express 23, 10564 (2015).

Return to Contents

+1 360 676 3290 · [email protected]

21

Conference 9726: Solid State Lasers XXV: Technology and Devices

9726-67, Session 12

White random lasing in mixture of ZnSe, CdS and CdSSe micropowders Ahmed Y. Alyamani, King Abdulaziz City for Science and Technology (Saudi Arabia); Maksim S. Leanenia, National Academy of Sciences of Belarus (Belarus); Lafi M. Alanazi, Maher M. Aljohani, Abdulaziz A. Aljariwi, King Abdulaziz City for Science and Technology (Saudi Arabia); Nikolay V. Rzheutskij, Evgeniy V. Lutsenko, Gennadiy P. Yablonskii, National Academy of Sciences of Belarus (Belarus) Room temperature random lasing with “white” light emission in a mixture of AIIBVI semiconductor powders was achieved for the first time. The scattering gain media was formed by the mixture of closely packed active micron sized crystallites of ZnSe, CdS and CdSSe semiconductors. The micropowders were produced by grinding bulk crystals of each compound. Optical excitation was performed by 10-nanosecond pulses of tuned Ti:Al2O3-laser at 390 nm. The lasing in the mixture of semiconductor powders was achieved simultaneously at four wavelengths in blue, green, yellow and red spectral regions after exceeding the threshold excitation power density. A drastic integral intensity increase, spectrum narrowing and appearance of mode structure accompanied the laser action. ZnSe crystallites produce the laser light at about 460 nm while CdS particles – at about 520 nm. Two types of CdSSe semiconductor micropowders with different sulfur content lase at 580 nm and 660 nm. The threshold excitation power densities for all laser lines in the emission spectrum are approximately the same of about 900 kW/cm2. The sum of the emission spectrum of the mixture of the micropowders forms “white” light with high brightness. Lasing is due to an appearance of random feedback for amplified radiation in the active medium of closely packed light scattering crystallites. The presented results may find their applications in visualization systems, lighting technology, data transmission, medicine as biosensors and in identification systems. The key feature of random lasers is low cost of its production and possibility to be deposited on any type of surface.

22

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII Monday - Thursday 15–18 February 2016 Part of Proceedings of SPIE Vol. 9727 Laser Resonators, Microresonators, and Beam Control XVIII

9727-1, Session 1

Solvent diffusion measurements using polymeric resonators based on whispering gallery modes Amir R. Ali, The German Univ. in Cairo (Egypt) and Southern Methodist Univ. (United States); Catherine Elias, Sara Iskander, Khalid Al-Agha, The German Univ. in Cairo (Egypt); Tindaro Ioppolo, Southern Methodist Univ. (United States) This paper presents an interaction study of solvent with the polymeric spheres. When a cross-linked polymer interacts with a solvent the polymer swells. This effect is due to diffusion of polymers and solvent molecules into each other. In turn, that leads to change in the optical and mechanical properties of the polymeric spheres. Several experiments were carried out to study the solvent induced whispering gallery modes (WGM) shift using microsphere immersed in a solvent atmosphere. In the preliminary experiments the microsphere is placed above the surface of three different solvents (Methanol, Ethanol and Hexane) and the measurements of the WGM shift signal are acquired using a 16 bit DAQ card and recorded on a PC. Results show the observed WGM shift is mainly due to three effects: (1) change in the index of refraction of the medium surrounding the sphere; (2) change in the index of refraction of the polymer due to solvent diffusion and (3) change in the microsphere radius due to swelling. This behavior has been examined using preliminary experiments to fully investigate this behavior.

9727-2, Session 1

Long period gratings based frequency selective interrogation of micro-resonators along the same fiber Daniele Farnesi, Istituto di Fisica Applicata “Nello Carrara” (Italy) and Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy); Francesco Chiavaioli, Francesco Baldini, Istituto di Fisica Applicata “Nello Carrara” (Italy); Giancarlo C. Righini, Centro Studi e Ricerche “E. Fermi” (Italy) and Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy); Silvia Soria, Cosimo Trono, Gualtiero Nunzi Conti, Istituto di Fisica Applicata “Nello Carrara” (Italy) Fiber optics sensors are ideal transducers for applications requiring devices that are durable, stable and insensitive to external perturbations. Additionally, they typically provide distributed or quasi-distributed measurement capability at multiple points. The goal of this work was to find an all-in-fiber coupling method to implement a quasi-distributed interrogation of whispering gallery mode (WGM) micro-optical resonators, which are known to exhibit unique properties for sensing. In a previous work, we proposed a configuration based on a long period grating (LPG) written in silica fiber followed by a thick fiber taper (with waist diameters in excess of 15 um), where coupling of cladding modes to WGMs occurs. This configuration is more robust than the standard fiber taper coupler but it does not allow interrogating more spheres coupled to the same fiber by monitoring the transmitted light. The new approach demonstrated in this work consists of replicating more times the same structure, which includes a second LPG (identical to the first one) that couples back the modulated light into the core. Typical Q-factors of the order of 10^8 and total

Return to Contents

coupling efficiency up to 60% were measured collecting the resonances of high-Q silica microspheres or microbubbles at the fiber end. Independent addressing of two different resonators at two different wavelengths (1519 nm and 1613 nm) along the same fiber was demonstrated.

9727-3, Session 1

Development of packaged silica microspheres coupled with tapered optical microfibres Pengfei Wang, Harbin Engineering Univ. (China); Ramgopal Madugani, Okinawa Institute of Science and Technology Graduate Univ. (Japan); Haoyu Zhao, College of Science, Harbin Engineering University (China); Jonathan Ward, Yong Yang, Light-Matter Interactions Unit, OIST Graduate University (Japan); Gerald Farrell, Dublin Institute of Technology (Ireland); Gilberto Brambilla, Univ. of Southampton (United Kingdom); Síle G. NicChormaic, Okinawa Institute of Science and Technology Graduate Univ. (Japan) Previously, microresonator-based add-drop filters have been developed, with silica fiber tapers used to efficiently couple evanescent fields to and from microresonators for their characterization and use. However, it is difficult to maintain stable alignment between microresonators and fiber tapers for an extended period, which is a disadvantage when fabricating add-drop devices for practical, real-world applications. In order to increase the mechanical stability of the microsphere resonator coupling system, in this research, a high quality silica microsphere was first coupled and packaged with two low-loss optical tapered fibers, and their relative positioning was optimized under an optical microscope and then fixed on a microscope slide using a low refractive index UV curable epoxy. The use of a coating epoxy significantly increased the mechanical alignment stability of the microsphere-fiber tapers system. At wavelengths near 1550 nm, a high-Q mode of up to 0.9?105 can be efficiently excited via evanescent coupling from the input tapered silica fiber. The temperature dependence of the packaged silica microsphere add-drop filter has also been investigated. In order to simplify the fabrication, a one-step fabrication process has been developed using a microsphere coupled to and then packaged with an optical microfiber coupler. Both of the packaging techniques offer the potential to develop low-cost, robustly-assembled fully integrated applications including WDM, sensors, ultra-small optical tunable filters and integrated micro-lasers due to the simplicity of the fabrication process compared with a conventional, costly photolithographic technique.

9727-4, Session 1

Observation of optically induced transparency in a micro-cavity (Invited Paper) Yuanlin Zheng, Jianjun Cao, Wenjie Wan, Shanghai Jiao Tong Univ. (China) Electromagnetically induced transparency (EIT) allows for rendering optical opaque transmission windows to a transparent one under illumination of a second coherent light beam. It was first observed in an atomic gas; intermediately, much attention has been drawn to its unique optical properties including: slowing light, all-optical switching, photon storage,

+1 360 676 3290 · [email protected]

23

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII etc. This opens up tremendous opportunities for information science. However, atomic gas systems requires optical cooling or vapor heating techniques combined with vacuum isolation, making it difficult for chipscale integrations. Alternatively, classical analogies mimicking EIT effect are under active pursuit in various physical systems, including coupled resonators, photonic crystals, and plasmonic meta-materials. However, most of them relying on the linear coupling between the resonances, can only exhibit EIT-like spectra but lacking of active-controlled transparency. Until recently, successful attempts have cloned the idea of EIT in an optomechanical micro-cavity to induce a narrow transparency with the aid of mechanical oscillations excited through Brillouin scattering nonlinearity, which provide phonons to couple some hybrid optical-mechanical resonances, similar to their counterparts: photons in the EIT. Here we report an optically induced transparency (OIT) scheme in a compact micro-cavity in ambient environment by exploring cavity-enhanced four-wave mixing gain to introduce a transparency window in an opaque resonance dip, which directly results from the interference between two resonances coupled nonlinearly through FWM process. Active-controlling of the OIT can be achieved by varying a strong pump beam. Furthermore, OIT observed here is a non-reciprocal one, since FWM gain is a unidirectional one owing to the conservation law of momentum.

9727-5, Session 1

Deterministic photon-atom and photonphoton interactions based on singlephoton Raman interaction (Invited Paper) Orel Bechler, Serge Rosenblum, Itay Shomroni, Yulia Lovsky, Gabriel Guendelman, Barak Dayan, Weizmann Institute of Science (Israel) I will present our progress toward the demonstration of a completely passive scheme for deterministic state transfer between a single photon and a single atom and vice versa. Based on a series of theoretical works [1-5], this scheme relies on a 3-level system coupled to a single mode waveguide (a single 87Rb atom interacting with a fibre-coupled microsphere resonator in our case). This scheme swaps a flying qubit, encoded in the two possible modes of the photon, with a stationary qubit, encoded in the two ground states of the atom: the state of the incoming photon is mapped to the state of the atom, and the state of the atom is mapped to the state of the outgoing photon [2]. Beyond performing as a passive photonic quantum memory, this scheme can in principle be modified to perform a universal quantum gate [3]. The scheme is completely passive, requiring no control fields beyond the single photons pulses. In the first experimental realization of this scheme [6], the state of the atom was shown to be determined by the direction of an in-coming single-photon pulse sent through the fiber. The state of the atom was read by a subsequent photon, thereby realizing all-optical switching of single photons by single photons. We then applied this scheme for demonstrating deterministic single-photon extraction from an incoming pulse with arbitrary number of photons [7]. This scheme, which can be applied with any atom-like 3-level L system, provides a building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons. [1] D. Pinotsi & A. Imamoglu, Phys. Rev. Lett. 100, 093603 (2008) [2] G. Lin, X. Zou, X. Lin, and G. Guo, Europhysics Letters 86, 30006 (2009) [3] K. Koshino, S. Ishizaka & Y. Nakamura, Phys. Rev. A 82, 010301(R) (2010) [4] S. Rosenblum, A.S. Parkins & B. Dayan, Phys. Rev. A 84, 033854 (2011) [5] S. Rosenblum & B. Dayan, arXiv: quant-ph 1412.0604 (2014) ) [6] I. Shomroni, S. Rosenblum, Y. Lovsky, O. Bechler, G. Guendelman & B. Dayan, Science 345, 903 (2014) [7] S. Rosenblum, O. Bechler, Y. Lovski, I. Shomroni, G. Guendelman, and B. Dayan, under review (2015)

24

9727-6, Session 2

High-Q GRIN resonators (Invited Paper) Andrea M. Armani, Soheil Soltani, Hyungwoo Choi, Vinh Diep, Andre Kovach, Kelvin Kuo, The Univ. of Southern California (United States) High and ultra-quality factor (Q) optical resonators have been used in numerous applications, ranging from biodetection and gyroscopes to nonlinear optics. In the majority of the measurements, the fundamental optical mode is used as it is easy to predict its behavior and subsequent response. However, there are numerous other modes which could give improved performance or offer alternative measurement opportunities. For example, by using a mode located farther from the device surface, the optical field becomes less susceptible to changes in the environment. However, selectively exciting a pre-determined, non-fundamental mode or, alternatively, creating a “designer” mode which has one’s ideal properties is extremely challenging. One approach which will be presented is based on engineering a gradient refractive index (GRIN) cavity. We use a silica ultra-high-Q toroidal cavity as a starting platform device. On top of this structure, we can controllably deposit, layer or grow different materials of different refractive indices, with nm-scale precision, creating resonators with a GRIN region co-located with the optical field. Slight adjustments in the thicknesses or indices of the films result in large changes in the mode which is most easily excited. Even in this architected structure, we have maintained Q>1 million. Using this approach, we have demonstrated the ability to tune the properties of the device. For example, we have changed the thermal response and the UV response of a device by over an order of magnitude.

9727-7, Session 2

Laser nanofabrication for advanced microcavities (Invited Paper) Hong-Bo Sun, Huai-Liang Xu, Xue-Peng Zhan, Qi-Dai Chen, Jilin Univ. (China) In summary, we have designed and fabricated 3D deformed polymer microcavity by FsLDW via two-photon polymerization, and demonstrated that these microlasers enable high Q-factor and single-mode lasing output with a low lasing threshold at room temperature. From the far field intensity distribution pattern, the deformed microcavities show that they can operate either highly unidirectional emission or single mode output, or both depending on the designs. Because the precise 3D fabrication capability of FsLDW and the good compatibility of polymer to other materials, the realization of the creation of active unidirectional lasers in polymer in this work provides an important step towards the functional integrated organic optoelectronic devices.

9727-8, Session 2

Elastomer photonics (Invited Paper) Diederik S. Wiersma, Karlsruher Institut für Technologie (Germany) and European Lab. for Non-linear Spectroscopy (Italy) and Consiqlio Nazionale delle Ricerche-istituto Nazionale di Ottica (Italy) In this contribution we report on the realization of photonic components with embedded elastomers that deform when they are illuminated with light. This allows to create tunable structures where a light beam influences the optical response of the structure and hence can influence the response to a signal beam. In particular, one can tune efficiently this way the resonance frequency of a high Q resonator, but also create strong (but slow) optical non-linearities

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-9, Session 2

III-V-semiconductor vertically-coupled whispering-gallery mode resonators made by selective lateral oxidation Stephane Calvez, Gaël Lafleur, Clément Arlotti, Alexandre Larrue, Pierre-Francois Calmon, Alexandre Arnoult, Guilhem Almuneau, Olivier Gauthier-Lafaye, Lab. d’Analyse et d’Architecture des Systèmes (France) Integrated whispering-gallery mode resonators are attractive devices which have found applications as selective filters, low-threshold lasers, high-speed modulators, high-sensitivity sensors and even as nonlinear converters. Their performance is governed by the level of detrimental (scattering, bulk, bending) loss incurred and the usable loss represented by the coupling rate between the resonator and its access waveguide. Practically, the latter parameter can be more accurately controlled when the resonator lies above the access waveguide, in other words, when the device uses a vertical integration scheme. So far, when using such an integration technique, the process involved a rather technically challenging step being either a planarization or a substrate transfer step. In this presentation, we propose and demonstrate an alternative method to fabricate vertically-coupled whispering-gallery mode resonators on III-V semiconductor epitaxial structures which has the benefit of being planarization-free and performed as single-side top-down process. The approach relies on a selective lateral thermal oxidation of aluminium-rich AlGaAs layers to define the buried access waveguide and enhance the vertical confinement of the whispering-gallery mode into the resonator. As a first experimental proof-of-principle of this approach, 75 µm-diameter micro-disk devices exhibiting quality factor reaching ~4500 have been successfully made. Further characterization results will be presented at the conference.

9727-10, Session 3

High-Q resonators for soliton combs and optical gyros (Invited Paper) Kerry J. Vahala, California Institute of Technology (United States) Two recent applications of nonlinear optics in high-Q microcavity systems will be described. First, the generation of highly coherent light in Brillouin microlaser systems will be examined. Experimental results in which this process is used for rotation sensing is then discussed. Rotation sensitivity of 20 degrees per hour is demonstrated. Second, the generation of frequency combs using dissipative solitons is discussed. Solitons are formed in silica disk resonators at a repetition frequency of 22 GHz. The solitons have a pulse width of 130 fs and are readily broadened. The phase noise of the detected pulse train is low in in the range of a good K-band oscillator.

9727-11, Session 3

Harmonic mode locking in a high-Q whispering gallery mode microcavity (Invited Paper) Takasumi Tanabe, Takumi Kato, Tomoya Kobatake, Ryo Suzuki, Akitoshi C Jinnai, Keio Univ. (Japan)

it is possible to realize all-optical modulation on-chip based on the Kerr effect at a record low power of 36 uW. I will also discuss the generation of optical Kerr combs, and talk about the dependence of the input power on the transition from modulation instability, multi-free-spectral range (FSR) mode locking, and 1-FSR mode locking. The hysteresis behavior caused by the optical bistability of a nonlinear cavity plays an important role at the transition between the states; and due to this hysteresis nature, the modelocking state in a low-order FSR is achieved only when we reduce the pump power after strong pumping. I will also describe the competition between four-wave mixing and Raman gain, and will show that the Raman comb becomes dominant during the transition between multi-FSR mode locking states.

9727-12, Session 3

To be announced (Invited Paper) Alexander L. Gaeta, Columbia Univ. (United States) No Abstract Available

9727-13, Session 4

Soliton induced Cherenkov radiation based chipscale frequency combs (Invited Paper) Victor Brasch, Michael Geiselmann, Martin H. P. Pfeiffer, Arne Kordts, Maxim Karpov, Hairun Guo, Michail Zervas, Junqiu Liu, Ecole Polytechnique Fédérale de Lausanne (Switzerland); Michael L. Gorodetsky, Lomonosov Moscow State Univ. (Russian Federation) and Russian Quantum Ctr. (Romania); Tobias J. Kippenberg, Ecole Polytechnique Fédérale de Lausanne (Switzerland) Discovered in 2007, microresonator (Kerr) frequency combs have emerged as an alternative and widely investigated method to synthesize optical frequency combs offering compact form factor, chip-scale integration, multi-gigahertz repetition rates, broad spectral bandwidth and high power per frequency comb line. Since their discovery there has been substantial progress in fundamental understanding and experimental realizations. Yet, in no demonstration could two key properties of optical frequency combs, broad spectral bandwidth and coherence, be achieved simultaneously. Here we overcome this challenge by accessing, for the first time, soliton induced Cherenkov radiation in an optical microresonator. By continuous wave pumping of a dispersion engineered, planar silicon nitride microresonator, continuously circulating, sub-30 fs short temporal dissipative Kerr solitons are generated that constitute a coherent optical frequency comb in the spectral domain. Emission of soliton induced Cherenkov radiation caused by higher order dispersion broadens the spectral bandwidth to 2/3 of an octave, sufficient for self-referencing and the broadest coherent microresonator frequency comb generated to date. Once generated it is shown that the frequency comb can be fully phase stabilized. The overall relative accuracy of the generated comb with respect to a reference fiber laser frequency comb is measured to be 3*10e-15. Our findings mark a critical milestone in the development of planar optical frequency combs, enabling applications in e.g. coherent communications, broadband dual comb spectroscopy and Raman spectral imaging. Our results underscore the utility and effectiveness of planar microresonator frequency comb technology, that offers the potential to make frequency metrology accessible beyond specialized laboratories.

A cavity with an ultrahigh quality factor (Q) and a small size is attractive because it can confine light in a tiny space and allow the strong integration of light and matter. A toroidal microcavity made of silica is of particular interest because it exhibits an ultrahigh Q/V, where V is the mode volume of the cavity. In addition, it can employ the Kerr effect. I will show that

Return to Contents

+1 360 676 3290 · [email protected]

25

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-14, Session 4

9727-17, Session 5

On-chip diamond frequency combs and Raman lasers (Invited Paper)

Mode control for square resonator microlasers

Marko Loncar, Pawel M. Latawiec, Vivek Venkataraman, Michael J. Burek, Harvard School of Engineering and Applied Sciences (United States)

Yong-Zhen Huang, Ming-Ying Tang, Yue-De Yang, Jin-Long Xiao, Yun Du, Institute of Semiconductors (China)

Owing to its wide bandgap, large linear & nonlinear refractive index, and excellent thermal properties, diamond is well suited for applications in nonlinear and high-power photonics. I will present our work on on-chip diamond frequency combs operating in telecom wavelength range, as well as the efforts aimed at realization of combs operating in the visible. In addition, I will discuss on-chip Raman lasers that emit at ~2 micron wavelength.

9727-15, Session 4

Dynamics and generation of microresonator frequency combs (Invited Paper) Chee Wei Wong, Shu-Wei Huang, Jinkang Lim, Abhinav K. Vinod, Jinghui Yang, Univ. of California, Los Angeles (United States); Heng Zhou, Univ. of Electronic Science and Technology of China (China)

Mode selection in square resonator semiconductor microlasers is demonstrated by adjusting the width of the output waveguide coupled to the midpoint of one side. The simulation and experimental results reveal that widely tunable single mode lasing can be realized in square resonator microlasers. Through adjusting the width of the output waveguide, the mode interval of the high-Q modes can reach four times of the longitudinal mode interval. Therefore, mode hopping can be efficiently avoided and the lasing wavelength can be tuned continuously by tuning the injection current. For a 17.8-?m-side-length square microlaser with a 1.4-?m-width output waveguide, mode-hopping-free single-mode operation is achieved with a continuous tuning range of 9.2 nm.

9727-18, Session 5

On the phase noise of Kerr comb RF photonic oscillators Andrey B. Matsko, Wei Liang, Danny Eliyahu, Vladimir Ilchenko, Anatoliy A. Savchenkov, Lute Maleki, OEwaves, Inc. (United States)

Recent advances in sub-wavelength nanoscale platforms have afforded the control of light from first principles, with impact to ultrafast sciences, optoelectronics and precision measurements. In this talk I will describe recent advances in chip-scale Kerr frequency comb oscillators. Coherent mode-locking is observed in the normal dispersion regime, verified by phase-resolved ultrafast spectroscopy at sub-100-attojoule sensitivities. A phase-locked frequency comb is also achieved over 3,600 modes spanning 65 THz at 18 GHz spacing. The normal dispersion architecture uncovers the mode-locking mechanisms in Kerr frequency combs, matched with firstprinciples coupled-mode theory, complementing our efforts on precision optical clocks.

Miniature radiofrequency (RF) photonic oscillators based on microresonator Kerr frequency combs generate the highest spectral purity RF signals compared with other electronic and photonic devices with similar size and power consumption. The low spectral frequency phase noise of the Kerr comb oscillators is comparable with the best frequency multiplied ovenized quartz oscillators, while the high spectral purity is similar to the phase noise of the lab scale RF photonic devices. Understanding fundamental limitations on the performance of Kerr comb oscillators is critically important for further development of the technology. In this presentation we review the major known noise sources of the Kerr comb oscillator and discuss possible methods for its improvement.

9727-16, Session 4

9727-19, Session 5

Optical frequency comb and spectroscopy with crystalline resonators in MIR (Invited Paper)

Third order nonlinear phenomena in silica solid and hollow whispering gallery mode resonators

Nan Yu, Jet Propulsion Lab. (United States)

Silvia Soria Huguet, Istituto di Fisica Applicata Nello Carrara (Italy); Daniele Farnesi, Istituto di Fisica Applicata Nello Carrara (Italy) and Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi” (Italy); Andrea Barucci, Franco Cosi, Istituto di Fisica Applicata Nello Carrara (Italy); Giancarlo C. Righini, Istituto di Fisica Applicata Nello Carrara (Italy) and Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi” (Italy); Gualtiero Nunzi Conti, Istituto di Fisica Applicata Nello Carrara (Italy)

High-Q whispering gallery mode resonators have been mostly studied in the visible and near-IR wavelength regions for optical frequency comb and spectroscopy. With crystalline materials, their use can be extended to the mid-IR beyond 2 µm where molecular gases not only have very rich characteristic spectral lines but also very large absorption cross sections. In this paper, we describe our continued efforts of pushing whispering gallery mode resonator applications in the MIR wavelength region, including Kerr comb generation and molecular absorption spectroscopy. With a variety of MIR transmitting crystalline materials, we have investigated their Q and limiting factors, dispersion and spectral engineering, parametric oscillation and comb generation. We have also explored the utility and limitation of using high Q resonators for ringdown molecular absorption measurements.

26

Dielectric microspheres and microbubbles can confine light and sound for a length of time through high quality factor whispering gallery modes (WGM). We report efficient generation of nonlinear phenomena related to third order optical non-linear susceptibility ?(3) interactions in resonant silica microspheres and microbubbles in the regime of normal dispersion. The interactions here reported are: Stimulated Raman Scattering (SRS), and four wave mixing processes comprising Stimulated Anti-stokes Raman

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII Scattering (SARS) and comb generation. SARS is always detected in presence of SRS, and never in the absence of SRS, in agreement with the theory of Bloembergen and Shen. Unusually strong anti-Stokes components and extraordinarily symmetric spectra have been observed. Resonant SARS and SRS corresponding to different Raman bands were also observed. The anti-Stokes Raman components are known to be coupled to the Stokes Raman ones, even for large dispersion. This coupling results in the growth of the anti-Stokes wave along the microresonator in direct proportion to the Stokes wave through an effectively phase-matched hyper-parametric process. A proof of the cavity-enhanced phenomenon is given by the lack of correlation among the pump, signal and idler: a resonant mode has to exist in order to obtain the pair of signal and idler.

9727-20, Session 5

Multi-scale nonlinear effects in whisperinggallery mode resonators Guoping Lin, Souleymane Diallo, Yanne K. Chembo, FEMTO-ST (France) Whispering-gallery mode resonators are known to host a wide variety of nonlinear behaviors. In particular, a large body of literature has focused on Kerr optical frequency combs in recent years. Here we investigate a wider range of nonlinear behaviors, including Brillouin, Raman, and thermo-optical effects. We first perform an experimental investigation in order to evidence the various nonlinear phenomena of interest. Basically, these phenomena involve nonlinear scattering at widely spaced spatial scales, including the electronic (for Kerr), molecular (for Raman), lattice (for Brillouin) and resonator (for thermal) scales. In our study, the host materials are fluoride crystals with a quality factor of the order of one billion at one micron. We then develop various spatiotemporal formalisms in order to investigate these nonlinear phenomena. Our theoretical analysis enables us to explore and understand how extreme events such as thermo-optical relaxation oscillations can be triggered in the resonator. Our study is complemented with numerical simulations that are in full agreement with the experimental findings.

with only ~85 mW pump threshold power in the feeding waveguide is shown along with continuous, mode-hop-free tuning over ~7.5 GHz in a compact, integrated-optics platform.

9727-22, Session 5

Novel ultrafast sources on chip: filter driven four wave mixing lasers, from high repetition rate to burst mode operation (Invited Paper) Alessia Pasquazi, Marco Peccianti, Univ. of Sussex (United Kingdom); Sai T. Chu, City Univ. of Hong Kong (Hong Kong, China); David J. Moss, RMIT Univ. (Australia); Roberto Morandotti, Institut National de la Recherche Scientifique (Canada) Passive fiber mode-locked lasers enable the excitation of multiple pulses per round trip representing a potential solutions for the increasing demand of practical optical sources with repetition rates of hundreds of GHz or higher. The control of such high repetition rate regimes is however a challenge. To this purpose, linear filters have been used in an “intracavity” configuration to force the repetition rate of the laser. This design is known as dissipative four wave mixing (DFWM) but it is usually unstable and hence marginally suitable for practical applications. We explore the use of nonlinear intracavity filters, such as integrated microring resonators, capable of “driving” the FWM interaction in the laser. We term this approach as Filter-Driven FWM.

9727-21, Session 5

With a proper choice of the filter properties in terms of free spectral range (FSR) and Q factor, we could observe stable regimes over a wide range of operating conditions, from high repetition rate oscillation at a 200GHz to the formation of two stable spectral comb replicas separated by the FSR of the main cavity (65MHz). High order filters, moreover, allow achieving nonlinear operation over large passbands. With an 11th order filter we achieve low-frequency mode-locking between the main cavity modes that oscillate within each resonance of the filter, producing burst pulsed operation. A stable mode-locked pulse train at 655GHz with an envelope of 42ps at 6.45MHz is achieved.

Diamond microresonator-based Raman laser at 2 ?m

9727-23, Session 6

Pawel Latawiec, Vivek Venkataraman, Michael J. Burek, Harvard Univ. (United States); Birgit J. M. Hausmann, Lawrence Berkeley National Lab. (United States); Irfan Bulu, Schlumberger-Doll Research Ctr. (United States); Marko Lon?ar, Harvard Univ. (United States) Fully integrated microresonator Raman lasers offer the ability to generate unique wavelengths of light on-chip. To date, device demonstrations have been confined to silica and silicon, limiting the scope of generated wavelengths. Here, we introduce an integrated Raman laser based on high quality-factor (>400,000) diamond racetrack resonators. Synthetic singlecrystal diamond is a promising platform for Raman lasers due to its giant Raman shift (~40 THz), large transparency window (from UV to THz) and excellent thermal properties yielding a greatly enhanced figure-of-merit compared to conventional materials. A polished diamond plate was thinned to specification (250 ?W, extending the functionality of diamond Raman lasers to a wavelength range at the edge of the mid-infrared useful for telecommunication. Continuous-wave operation

Return to Contents

Using mechanics to convert between microwave and optical frequencies (Invited Paper) Amit Vainsencher, Kevin J Satzinger, Greg A Peairs, University of California - Santa Barbara (United States); Andrew N. Cleland, Univ. of California, Santa Barbara (United States) We are building nanoscale interfaces to convert coherently between optical and microwave frequencies, ultimately to provide a quantum interface between different qubits operating at microwave frequencies, linked by an optical telecommunications channel. The design is based on piezoelectric optomechanical crystals that co-locate a high quality factor optical and a mechanical resonance in the same sub-micron scale volume, allowing very strong parametric interactions between the two modes. Building these structures from piezoelectric materials allows a strong electromechanical transduction, thus coupling an electric signal at a few GHz to the mechanical resonance at the same frequency. This then allows bilateral parametric coupling between the microwave electrical signal and a 1550 nm telecommunications signal. I will report on progress in this effort.

+1 360 676 3290 · [email protected]

27

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-24, Session 6

Droplet’s acoustics Raphael Dahan, Technion-Israel Institute of Technology (Israel) Droplets represent a basic liquid structure that is contained by interfacial tension while bounded almost completely by free surfaces. Such droplets can host three types of resonances: optical-, capillary- and acousticalones. Contrary to their capillary resonances (Rayleigh, 1879) and to optical resonances (Ashkin, 1977), droplets’ acoustical resonances were rarely considered. The challenge lies in the fact that ?droplets’ acoustics requires modulating forces at MHz rates. Here we rely on optical forces (that can act sufficiently quickly) to experimentally excite acoustical resonances at 37 MHz that starts vibrating at an optical threshold of 68 ?W. The optical modes that we are using as a mechanical exciter are circulating in the 40 ?m drop with a ?108 quality-factor. Our results open an experimental access to the acoustical resonances of droplets, which were rarely considered, neither theoretically nor experimentally.

9727-25, Session 6

Optical binding in white light Shai Maayani, Technion-Israel Institute of Technology (Israel) We experimentally demonstrate, for the first time, binding of aeroslols with a variety of sizes and shapes in white light. The optomechancial interaction between particles is long range and at the underdamped regime. Incoherency allows mitigation of interference fringes to enable monotonically changing the distance between particles from 60 micron to touching - constituting a parametrically controlled testbed for transition studies at new scales.

9727-26, Session 6

Tweezers controlled resonator Leopoldo L. Martin, Samuel Kaminski, Technion-Israel Institute of Technology (Israel) We experimentally demonstrate trapping a micro-droplet with an optical tweezers and then functionalize it as a micro-resonator by bringing it close to a tapered fiber coupler. Our tweezers facilitated tuning of the coupling from the under-coupled to the critical coupling regime with an optical Q of 12 million and micro-resonator size at the 85 um scale. We prove the concept of using an optical trap for activating oil droplets as fiber-coupled micro-resonators. We believe that our technique will extend to several resonators and then to an optical circuit where the shape and position of many optical devices will be controlled. Our long-term vision includes optical circuits where a multi-minima optical trap shapes and positions multiple resonators. Being practical, we start here with modestly proving this concept by activating one drop as a resonator, and using an optical trap to hold and position it next to a tapered-fiber coupler.

9727-27, Session 7

Field mappers for laser material processing Paul Blair, Matthew O. Currie, Natalia Trela, Howard J. Baker, Eoin Murphy, Duncan Walker, Roy McBride, PowerPhotonic Ltd. (United Kingdom)

28

The native shape of the single-mode laser beam used for high power material processing applications is circular with a Gaussian intensity profile. Manufacturers are now demanding the ability to transform the intensity profile and shape to be compatible with a new generation of advanced processing applications that require much higher precision and control. We describe the design, fabrication and application of a dual-optic, beamshaping system for single-mode laser sources, that transforms a Gaussian laser beam by remapping – hence field mapping - the intensity profile to create a wide variety of spot shapes including discs, donuts, squares and rectangles. The optic pair transform the intensity distribution and subsequently flatten the phase of the beam, to generate spot sizes and depth of focus close to that of a diffraction limited beam. The field mapping approach to beam-shaping is a refractive solution that does not add speckle to the beam, making it ideal for use with single mode laser sources. We describe a manufacturing process for refractive optics in fused silica that uses a freeform direct-write process that is especially suited for the fabrication of this type of freeform optic. The beam-shaper described above was manufactured in conventional UV-fused silica using this process. The fabrication process generates a smooth surface (106) and capillarybased microfluidics. In the OFRR, the circular shaped capillary cross section forms the optical ring resonator that supports the optical whispering gallery modes (WGMs) traveling along the circumference. The WGM has an evanescent field extended into the capillary core, and therefore, interacts with molecules inside the capillary. This presentation sits at the intersection of photonics, micro/nanofluidics, mechanics, biomedicine, nanobiotechnology, and analytical chemistry, as well as nanoelectronics and fundamental physics. I will start with the introduction of the OFRR, describing its optical and mechanical properties. Then I will discuss how to utilize the OFRR technology platform in the following vastly different areas: (1) label-free biosensing; (2) microfluidic optomechanics; (3) optofluidic laser; and (4) multi-dimensional microgas chromatography. Finally, if time permits, I will discuss how we expand the OFRR concept, i.e., synergy of photonics and microfluidics, to detect analytes in vapor and liquid phases at the molecular or cellular level for various applications, and to develop novel photonic devices whose performance can be precisely controlled by biological processes and interactions.

Frank Vollmer, Max-Planck-Institut für die Physik des Lichts (Germany)

Return to Contents

+1 360 676 3290 · [email protected]

33

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-67, Session 10

9727-42, Session 11

Whispering-gallery mode resonator sensors based on liquid droplets

Microfluidic determination of vitamin D3 and its binding protein using a fluorescent cylindrical microcavity

Rosa Zullo, Antonio Giorgini, Saverio Avino, Pietro Malara, Paolo De Natale, Gianluca Gagliardi, Istituto Nazionale di Ottica (Italy) Over the last decade, optical whispering-gallery modes (WGMs) have been observed in solid micro-cavities of various geometries and materials showing Q factors higher than 109. These resonators were studied for laser emission, non-linear optics, comb generation and recently proved ultra-sensitive bio-chemical probes. The peculiarity of WGMs supported by dielectric microspheres and toroids is that light travels along closed paths at the interface between the surface of the resonator and the surrounding environment. Unfortunately, most of the light circulates inside the resonator and only a small fraction is actually used for light-matter interaction, thereby reducing the effective cavity enhancement. Here, we propose to use liquid droplets as micro-resonators for sensing applications. The droplet itself serves as the cavity and the sample at the same time, where the internal optical field is directly used to probe dissolved analytes or particles. We demonstrate free-space excitation and laser frequency locking on whispering-gallery modes in vertically-suspended liquid droplets. The Q-factor limit is investigated by means of cavity photon lifetime measurements performed with cavity ring-down techniques. Q-factors ranging from 105 to > 107 are observed in the near-infrared and visible spectral regions. Mixtures made from different liquids are also used as a proof-of-concept of chemical sensing. The droplet system appears very promising for applications to spectroscopy, biosensing, material characterization and non-linear optics.

9727-41, Session 11

Quantum dot optofluidic lasers and their prospects for biochemical sensing (Invited Paper) Alper Kiraz, Koç Univ. (Turkey) and Univ. of Michigan (United States); Qiushu Chen, Univ. of Michigan (United States); Mehdi Aas, Koç Univ. (Turkey); Alexandr Jonas, Istanbul Technical Univ. (Turkey); Xudong Fan, Univ. of Michigan (United States) We achieved three types of laser emissions with aqueous quantum dots (QDs) using the same high-Q-factor optofluidic ring resonator (OFRR) platform. In the first type, 2 ?M QDs were in bulk buffer solution that filled the entire OFRR cavity volume. The lasing threshold was 0.1 ?J/mm2, over 3 orders of magnitude lower than the state-of-the-art. In the second type, the QDs were immobilized as a single layer on the interface between the OFRR inner wall and buffer solution with a surface density as low as 3 ? 109–1010 cm–2. The lasing threshold of 60 ?J/mm2 was achieved. In the third type, we achieved optofluidic FRET lasing using QDs as FRET donors and Cy5 dye molecules as acceptors. We observed lasing from Cy5 emission band in QDCy5 pair when excited at QD absorption band, far away from Cy5 absorption maximum. The demonstrated capability of QDs as donors in FRET lasers greatly improves the versatility for optofluidic laser operation due to the broad and large absorption cross-section of QDs in the blue and UV range. I will also discuss the comprehensive theoretical analysis of optofluidic FRET lasers that we have performed based on a Fabry-Perot microcavity using a rate equation model. By comparing FRET lasing-based sensors with conventional sensors using FRET signals obtained by spontaneous fluorescence emission, we show that for optimal pump fluence and FRET pair concentration, FRET lasing can lead to more than 100-fold enhancement in detection sensitivities of conformation changes for linker lengths in the Förster radius range.

34

Stephen Lane, Peter West, Univ. of Alberta (Canada); Alexandre François, The Univ. of Adelaide (Australia); Al Meldrum, Univ. of Alberta (Canada) We developed a microfluidic optical resonance biosensor and demonstrated its refractometric and biosensing performance. The device uses the whispering gallery modes (WGMs) that form within a glass capillary whose channel walls are coated with a high-index layer of fluorescent silicon quantum dots (QDs). These cylindrical resonances appear as periodic maxima in the fluorescence spectrum emitted by the quantum dots. Here we utilize the WGMs of a fluorescent core microcapillary for protein detection. The device is comprised of a glass microcapillary with a 50-?m-diameter inner channel coated with a thin film of silicon QDs. Most of the resonant electromagnetic field of the WGMs is contained within the QD layer but a fraction extends into the capillary channel where it samples a fluidic analyte pumped inside. Changes in the local analyte refractive index cause shifts in the resonant WGM wavelengths, providing the sensing transduction mechanism. The refractometric sensitivity of this device was found to be between 3 and 24 nm per refractive index unit depending on the QD film thickness. Biosensing was demonstrated using the biotin-avidin system, by first functionalizing the channel surface (i.e., the QD film) with amine-terminated polyelectrolyte layers. This fluorescent device showed concentration detection limits on the order of 10 nM, and an equilibrium association constant of 1.1 x 106 M-1 for the biotin-neutravidin interaction. We then demonstrated the nonspecific binding of vitamin D binding protein as the first step toward developing a microfluidic competition assay for vitamin D.

9727-43, Session 11

Flow sensor using a hollow WGM microlaser Jonathan M. Ward, Yong Yang, Síle G. NicChormaic, Okinawa Institute of Science and Technology Graduate Univ. (Japan) Optical sensing of flow in microfluidic systems is an important area of study. Flow sensing using the concept of a “hot WGM microlaser” is presented. Silica microcapillary or microbubble whispering gallery resonators were coated with a layer of laser glass, in this case Yb:Er doped phosphate glass. This was realised by the fact that the two glasses have different melting points. A CO2 laser was used to melt a small piece of doped glass wire onto an 80 µm silica capillary. The power of the CO2 laser was controlled to flow the doped glass around the capillary. The resulting geometry is a hollow microbottle shaped resonator. The Er:Yb doped glass outer layer was pumped at 980 nm via a tapered optical fiber and whispering gallery mode (WGM) lasing was recorded at 1535 nm. Gas was then passed through the capillary and the WGMs were observed to shift towards shorter wavelengths due to the cooling effect of the gas flow. In this way thermal tuning of the lasing modes over 70 GHz was achieved. The end of the capillary was connected to a mass flow sensor and the WGM shift rate as a function of flow rate and pump laser power was measured. Results were fitted using the theory of hot wire anemometry. Flow sensing can also be realized when the cavity is passively probed at 780 nm. At this wavelength the Q factor of the WGMs was estimated to be in excess of 105.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-44, Session 11

Localized biomolecules immobilization in optical microbubble resonators Simone Berneschi, Francesco Baldini, Andrea Barucci, Istituto di Fisica Applicata “Nello Carrara” (Italy); Alessandro Cosci, Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy) and Istituto di Fisica Applicata “Nello Carrara” (Italy); Franco Cosi, Istituto di Fisica Applicata “Nello Carrara” (Italy); Daniele Farnesi, Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy) and Istituto di Fisica Applicata “Nello Carrara” (Italy); Gualtiero Nunzi Conti, Istituto di Fisica Applicata “Nello Carrara” (Italy) and Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy); Giancarlo C. Righini, Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy); Silvia Soria, Sara Tombelli, Cosimo Trono, Istituto di Fisica Applicata “Nello Carrara” (Italy); Stefano Pelli, Istituto di Fisica Applicata “Nello Carrara” (Italy) and Museo Storico della Fisica e Ctr. Studi e Ricerche “Enrico Fermi” (Italy); Ambra Giannetti, Istituto di Fisica Applicata “Nello Carrara” (Italy) Optical microbubble resonators (OMBRs) are gaining more and more interest as suitable platform for sensing applications because they combine the whispering gallery mode (WGM) resonator properties with an embedded microfluidics. In particular, their operation as optical biosensors is based on the fact that, for a suitable value of the OMBR wall thickness, the WGM optical field extends on both sides of the wall. Therefore the inner surface can be used for the interaction with the analyte inside the flowing fluid and the outer one for the resonance excitation by an external guiding structure (i.e.: a tapered fiber or an optical waveguide). Due to the morphological dependence of the WGMs, any change on the OMBR inner surface related to any biochemical bond causes a shift of the resonances and produces a resonance linewidth broadening with a decrease of the Q factor value. By measuring these changes, information about the concentration of the analyte to be detected can be achieved. A crucial step for the development of an OMBR – based biosensor is constituted by the functionalization of its inner surface. Here we report on the development of an ad-hoc spatially selective photo-chemical procedure, concerning a localized immobilization of fluorescent biomolecules on the OMBR inner surface, able both to maintain high Q factor (> 10^5) for the optical transducer in buffer solution and to guarantee that the OMBR is the unique biosensing element of the overall optical device. The OMBR characterization involves fluorescence microscopy and real time measurement of the resonance broadening.

9727-45, Session 11

Optical heterodyne detection for ultrahigh Q micro-disk laser sensor Myung-Gi Ji, Byung-Hee Son, Tae-Ryong Kim, Mi Jung, Chung-Ang Univ. (Korea, Republic of); Hong-Seung Kim, Chil-Min Kim, Daegu Gyeongbuk Institute of Science & Technology (Korea, Republic of); Kwang Ryong Oh, Electronics and Telecommunications Research Institute (Korea, Republic of); Young-Wan Choi, Chung-Ang Univ. (Korea, Republic of) In this paper, we propose a bio-sensing method using optical heterodyne detection based on optical technique for ultra-high Q micro-disk laser (MDL) as sensor platform. MDL structure with ultra-high Q-factor(~108) has advantages in detecting a small variation of the lasing wavelength.

Return to Contents

For example, when a single molecule is attached to sidewall of MDL, the lasing wavelength is changed by sub-pico meter. Optical spectrum analyzer(OSA) has limits to detect sub-pico meter variation in the resonant wavelength because of the spectral resolution. In order to overcome this limitation, we used a heterodyne detection method which needs two MDLs with the same characteristics. One is used as a reference laser which has a 1550 nm lasing wavelength(?1), and the other laser is used as a sensor for the detection of molecules attached to sidewall of MDL structure. In that case, sub-pico meter variation in lasing wavelength ?1 +?? (sub-pico meter) can be expected. We performed a heterodyne detection using light beating, and measured ?? changing a sub-pico meter wavelength band to beating frequency ranging from several hundred MHz to several GHz band.

9727-46, Session 11

Water-walled microfluidics Shai Maayani, Technion-Israel Institute of Technology (Israel) Liquids serve microcavity research ever since Ashkin’s studies on optical resonances in levitating droplets to recent optofluidic resonators. Droplets can provide optical quality factor (Q) in proximity to the limit restricted by water absorption and radiation loss. However, water micro-drops vaporize quickly due to their large area/volume ratio. Here we fabricate a water-air interface that almost entirely surrounds our device, allowing for >1,000,000 recirculations of light (finesse). We sustain the droplets for >16 hours using a nano-water-bridge that extends from the droplet to a practically-unlimited distant-reservoir that compensates for evaporation. Our device exhibits surface tension 8000-times stronger than gravity that self-stabilizes its shape to a degree sufficient to maintain critical coupling as well as to resolve split modes. Our device has 98% of their surrounding walls made strictly of water-air interfaces with concave, convex or saddle geometries, suggesting an arbitrary-shape microfluidic technology with water-walls almost all-over.

9727-47, Session 11

Spinning optical resonator sensor for torsional vibrational applications measurements Amir R. Ali, The German Univ. in Cairo (Egypt) and Southern Methodist Univ. (United States); Andrew Gatherer, Rice Univ. (United States) Spinning spherical resonators in the torsional vibrational applications could cause a shift in its whispering gallery mode (WGM). The centripetal force acting on the spinning micro sphere resonator will leads to these WGM shifts. An analysis and experiment were carried out in this paper to investigate and demonstrate this effect using different polymeric resonators. In this experiment, centripetal force exerted by the DC-Motor on the sphere induces an elastic deformation of the resonator. This in turn induces a shift in the whispering gallery modes of the sphere resonator. Materials used for the sphere are polydimethylsiloxane (PDMS 60:1 where 60 parts base silicon elastomer to 1 part polymer curing agent by volume) with shear modulus (G=1kPa), (PDMS 10:1) with shear modulus (G=300kPa), polymethylmethacrylate (PMMA, G=2.6*10^9GPa) and silica (G=3*10^10 GPa). The sphere size was kept constant with 1mm in diameter for all above materials. The optical modes of the sphere exit using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts. The results showed the resonators with smaller shear modulus G experience larger WGM shift due to the larger mechanical deformation induced by the applied external centripetal force. Also, the results show that angular velocity sensors used in the torsional vibrational applications could be designed using this principle.

+1 360 676 3290 · [email protected]

35

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-48, Session 12

A beam quality measure for cylindrical vector beams (Invited Paper) Andrew Forbes, Bienvenu I. Ndagano, Melanie G. McLaren, Univ. of the Witwatersrand (South Africa) In the 1990s statistical techniques were applied to laser beams with the result that new measures were introduced to define the beam quality. The moment analysis could be applied to any beam, returning a quantitative measure of its ?quality?. The value of the approach was that the quality could be described by a single number. In this work we apply tools from quantum mechanics to find a single quality factor for how ?vector? a vector beam really is. The applicability of quantum tools to these beams is due to the inherent non-separability of vector beams, a trait they share with entangled quantum states. We show how to practically implement this in the laboratory and show how the approach may be used to monitor degradation in vector beams from lasers, for example, radially polarized laser beams.

9727-49, Session 12

Selective generation of LaguerreGaussian mode output in double resonator configuration Ji Won Kim, Dong Joon Kim, Eun Jee Park, Hanyang Univ. (Korea, Republic of); Minjee Jeon, Hanyang Univ. (Korea, Republic of) and Korea Institute of Industrial Technology (Korea, Republic of); Hoon Jeong, Korea Institute of Industrial Technology (Korea, Republic of) We report a simple technique to allow selective generation of the LaguerreGaussian mode (LG0n) output in an end-pumped Nd:YAG laser. Our approach employs the double resonator configuration, which is composed of two cavities sharing a single gain medium and an input coupling mirror but having two resonating beams of different output coupling with the aid of an intracavity polarizer. Since the population inversion density in the gain medium is determined by the threshold of the first excited cavity (secondary cavity), the other cavity (the primary cavity) using a higher transmittance output coupler cannot lase on the same transverse mode due to the higher threshold level. As a result, we can select the excited transverse mode of the primary cavity simply by controlling the lasing condition of the secondary cavity. Based on this approach, we already demonstrated selective excitation of the fundamental Gaussian TEM00 or the first-order LaguerreGaussian LG01 mode and, moreover, generation of the laser output with a tailored beam profile in an end-pumped Nd:YAG laser. Here, we extend our technique to generate a higher order LG mode output in an Nd:YAG laser yielding the LG01, LG02 or LG03 mode output with well-determined helical wavefronts. The prospects of power scaling and further improvement will be discussed along with the underlying mechanism and the previous results.

9727-51, Session 12

Beam control through nonlinear propagation (Invited Paper) Jean Claude M. Diels, Ladan Arissian, The Univ. of New Mexico (United States) Diffraction and atmospheric distortion limits the propagation of laser beams. “Filamentation was presented as a solution, by self-trapping intense beams, with the transmission limited “only” by nonlinear effects. The “only” evolved in a plethora of parameters to control . . . and understand. In this field of light matter interaction it becomes difficult to distinguish the controlling from the controlled parameter. The power of the original beam is drained by emission at various wavelengths. Two types of mechanisms are involved in generating these wavelengths: (i) emission from individual molecules (self-phase modulation, shock, fluorescence), and (ii) collective mechanisms (four wave mixing, inversion gain) where the new wavelengths are amplified by a group of molecules. With ultrashort pulses, the amplification at a particular wavelength proceeds along a direction group velocity matching. Resonant amplification occurs when a population inversion is created between electronic, vibrational and rotational levels; inversion affected by molecular orientation, which is in turn controlled by the beam polarization. The filamented beam can be controlled through the seeding process (involving single molecules) and the amplification process. Seeding of new wavelengths is considerably reduced by starting with long, bandwidth limited pulses, and/or a beam waist in vacuum as initial condition. Filaments produced with GHz bandwidth UV pulses are presented, which do not loose energy to “conical emission”. It will be shown how control of the amplification process is made through manipulation of the initial beam polarization. The continuum spectrum, as well spectral lines can be enhanced through polarization control.

9727-52, Session 13

Largest in the world bimorph deformable mirror for high-power laser beam correction (Invited Paper) Alexis V. Kudryashov, Moscow State Univ. of Mechanical Engineering (Russian Federation)

9727-50, Session 12

1 kW monolithic linearly polarized narrow linewidth single-mode fiber laser Wei Shi, Tianjin Univ. (China); Qiang Fang, HFB Photonics, Inc. (China) High power narrow linewidth linearly polarized fiber lasers have been widely utilized in various applications, such as the nonlinear frequency conversion, coherent laser beam combining etc. The power scaling for the narrow linewidth fiber lasers is challenging mainly due to the limitation from the stimulated Brillouin scattering (SBS). However, when the laser linewidth is broadened to GHz level, which is much greater than the bandwidth of the

36

Brillouin gain spectrum, the SBS threshold will be enhanced significantly and the power scaling for these narrow linewidth lasers is easier accordingly. In this paper, we report a kilowatts-level, narrow linewidth, all-fiber format, linearly polarized laser source at 1064 nm in master oscillator-power amplifier (MOPA) configuration. The laser source consists of a linearly polarized, narrow linewidth (~20 GHz) double cladding (DC) fiber laser oscillator and two stages of linearly polarized DC fiber amplifiers. A linearly polarized laser beam with >1kW average power, ~ 35 GHz linewidth, >14.4 dB polarization extinction ratio (PER), and diffraction-limited beam quality (M2 < 1.1), was achieved. The high power narrow linewidth, transform-limited laser are pretty suited for coherent beam combining, seeding high power Nd:YAG laser, nonlinear laser frequency conversion, etc.

Here we report the design and installation of the largest bimorph deformable mirror (420x480 mm). This mirror is intended to correct for the aberrations of the final amplifier in FIREX laser complex in Osaka University (Japan). Initial surface and main optical properties of such a mirror are presented. Response functions of all 120 electrodes were investigated. The results of mirror test showed the possibility to build of such kind of mirrors with the size of 500 mm and larger apertures.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9727: Laser Resonators, Microresonators, and Beam Control XVIII

9727-53, Session 13

Discrete excitation of mode pulses using a diode-pumped solid-state digital laser Sandile Ngcobo, Teboho Bell, CSIR National Laser Ctr. (South Africa) No Abstract Available

9727-54, Session 13

Intracavity generation of low-loss radialorder Laguerre-Gaussian modes using digital holograms Lebohang T. Bell, Council for Scientific and Industrial Research (South Africa); Kamel Äit-Ameur, ENSICAEN (France); Andrew Forbes, Univ. of KwaZulu-Natal (South Africa); Sandile Ngcobo, Council for Scientific and Industrial Research (South Africa) Laguerre-Gaussian, LGpl, modes of radial-order p and azimuthal order l=0 were generated inside the resonator. By using amplitude mask encoded on digital holograms, that were displayed on a spatial light modulator, acting as an end-mirror of the resonator. The digital holograms were encoded to act as an amplitude mask that contained absorbing rings that matched the zeros of the desired Laguerre-Gaussian mode. We show that we can generate LGp0 of p=0 to p=4, when using full circular absorbing rings and also when using half circular absorbingrings. We will demonstrate the advantages associated with using half circular absorbing rings. We observed that the laser resonator will have a lower threshold, while at the same time maintain the same laser characteristics. The characteristics such as; slope efficiency, mode purity and beam quality factor.

Return to Contents

+1 360 676 3290 · [email protected]

37

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications Monday - Thursday 15–18 February 2016 Part of Proceedings of SPIE Vol. 9728 Fiber Lasers XIII: Technology, Systems, and Applications

9728-1, Session 1

9728-3, Session 1

Multi-kilowatt power scaling and coherent beam combining of narrow-linewidth fiber lasers (Invited Paper)

Kilowatt high-efficiency narrow-linewidth monolithic fiber amplifier operating at 1034 nm

Iyad Dajani, Angel Flores, Roger H. Holten, Thomas Ehrenreich, Air Force Research Lab. (United States)

Nader A. Naderi, Angel Flores, Kenneth B. Rowland Jr., Iyad Dajani, Air Force Research Lab. (United States)

In contrast to stimulated Brillouin scattering (SBS) where larger mode field areas can lead to greater suppression in fiber amplifiers, the modal instability (MI) threshold is typically reduced with increased core sizes. Consequently, the fiber SBS/modal instability threshold tradeoff plays a key role for further power scaling. We report results from two ~1.5kW, all-fiber Yb-doped amplifiers with comparable optical to optical efficiencies and effective linewidths; one with a 25µm core fiber from Nufern and one with a 20µm core fiber from LEIKKI. SBS suppression in both amplifiers was achieved through pseudo-random bit sequence (PRBS) phase modulation which has proved to be more effective than white noise source. Both amplifiers can provide fringe visibilities >90% when a sample of the output is coherently combined with a low power channel. While the power output from the 25µm core fiber was MI limited at ~1.5 kW, no sign of MI was observed in the smaller core fiber. Furthermore, there were strong indications that the Brillouin gain coefficient was substantially lower in the 20µm core fiber. Overall, this may allow us to utilize the higher MI threshold 20µm fiber to scale further in power while maintaining sufficiently narrow linewidth for either coherent or spectral beam combination. Finally, as a demonstration of the combinability of multiple kW class amplifiers driven by PRBS phase modulation, we coherently combined 5 commercial amplifiers using a 1x5 diffractive optical element leading to a 5 kW beam with a measured M2 value of 1.06. The combining efficiency was 82%.

Development of Yb-doped fiber lasers has seen rapid progress with emerging wide range of applications. Operating at shorter wavelengths of the gain bandwidth is desired due to lower quantum defect heating which may be beneficial in suppressing the modal instability (MI), and in order to expand the wavelength range in spectral beam combining architectures. To date, high-power narrow-linewidth monolithic fiber amplifiers operating at wavelengths 1.5kW output power and M2-value of the beam 6 kW. The leap to subps operation of these lasers systems opens the door for a wide range of exciting applications and experiments including mid-IR supercontinuum generation, mid-IR fiber based frequency combs, human tissue surgery, and sensitive broadband trace gas detection. Here, we review the progress from initial Q-switched laser systems generating 100 ns pulses with < 0.1 kW peak power all the way to the subps, multi-kW level mode-locked systems. The potential for these systems to be a driver for mid-IR fiber laser frequency comb sources is explored in detail, including calculations of supercontinuum and coherence. Finally, a view towards the future of ultrashort pulse generation in these systems is presented, with a particular emphasis on creating sub-100 fs gainbandwidth limited pulses directly from the oscillator.

9728-22, Session 5

Mid-infrared supercontinuum generation up to 4.6 µm using step-index indium fluoride fiber pumped by a femtosecond fiber laser near 2 µm (Invited Paper) Reza Salem, Thorlabs Quantum Electronics (United States); Zhuo Jiang, Dongfeng Liu, Robert M. Pafchek, Paul Foy, Mohammed Saad, Doug Jenkins, Alex E. Cable, Peter Fendel, Thorlabs Inc. (United States) We report mid-infrared supercontinuum (SC) generation in a dispersionengineered step-index indium fluoride fiber pumped by a femtosecond fiber laser around 2 µm. The SC spans 1.8 octaves from 1.25 µm to 4.6 µm with an average output power of 270 mW. The pump source is an all-fiber femtosecond laser that generates sub-100-fs pulses at 50 MHz repetition rate with 570 mW average power. The SC-generation fiber is engineered through core size and numerical aperture adjustments to have a zerodispersion wavelength close to 1.9 µm. The fiber dispersion is calculated to be small and anomalous at the pump wavelength and to maintain a small absolute value (90% optical-to-optical efficiency in Tm:fiber lasers. Holmium, on the other hand, generally enables longer wavelength operation with low quantum defect; however, efficiencies 90 nm of continuous tuning range

Mateusz Wysmolek, Hakan Sayinc, Laser Zentrum Hannover e.V. (Germany); Samir Lamrini, Peter Fuhrberg, LISA Laser Products OHG (Germany); Kristian Lauritsen, Dietmar Klemme, PicoQuant GmbH (Germany); Uwe Morgner, Laser Zentrum Hannover eV (Germany) and Leibniz Univ. Hannover (Germany); Jörg Neumann, Dietmar Kracht, Laser Zentrum Hannover e.V. (Germany)

Robert A. Stegeman, Eric D. Park, Q-Peak, Inc. (United States)

High energy nanosecond pulsed laser systems are finding numerous applications in material processing, nonlinear frequency conversion, free space data transmission etc. Arbitrary pulse forming allows for pulse generation tailored to the application or compensation of energy saturation in an amplifier leading to pulse deformation. In our approach we are using a directly modulated semiconductor laser diode emitting at 1950 nm with a PC controlled laser diode driver. The pulse shape is pre-defined by high precision software and can be changed on the fly making an external arbitrary pulse form generator unnecessary. Furthermore, the same software allows for the control of the pulse repetition rate and the generation of pulse bursts making it a promising candidate for material processing. Due to the low output power, the use of 3 fiber amplifier stages is necessary to achieve adequate energies for material processing. With the presented MOPA system we were able to achieve 30 kW of peak power with clean 10 ns pulses free from spectral and temporal deteriorations. The system is a robust and fully alignment free monolithic fiber setup. An unique feature is a computer controlled seed module with advanced control of pulse shape and repetition rate with burst mode option. To the best of our knowledge this is a first presentation of arbitrary pulse shaping and amplification to 100s µJ pulse energies in Tm3+ doped fibers.

9728-36, Session 8

Chirped pulse amplification of a dissipative soliton thulium-doped fiber laser Fangzhou Tan, Hongxing Shi, Peng Wang, Jiang Liu, Pu Wang, Beijing Univ. of Technology (China) We demonstrate on chirped pulse amplification of a dissipative soliton thulium-doped fiber laser. It consists of an all-fiber seed laser, a fiber-based stretcher, two-stage fiber amplifier and free space grating compressor. The oscillator works in the normal dispersion regime and delivers up-chirped pulses with output power of 3 mW at repetition rate of 29.3 MHz. The spectrum of the seed laser is located at 1938 nm with a 10 dB bandwidth of 50 nm. The output pulses is then stretched in ~50 m normal dispersion fiber to 72 ps pulse duration. A single- mode single-clad fiber amplifier is used to amplify the pulse energy to 1.78 nJ. A polarization controller is used after the pre-amplifier to change the polarization of the pulses after passing through a polarization maintaining (PM) isolator. In the main amplifier, a single-mode double-clad polarization maintaining Tm-doped fiber amplifier is used to boost the pulse energy to 229 nJ corresponding to an average power of 6.72 W, with a slope efficiency of 32.7 %. The amplified up-chirped pulses could be dechirped to a duration of 130 fs with energy of 153 nJ.

Tunable Tm-doped fiber laser sources are an attractive solution for chemical detection, medical lasers, and in conjunction with amplifiers, seeding of nonlinear optical processes. Tunability for Tm-doped fiber lasers traditionally comes from an external grating to provide cavity feedback, which has inherent instabilities associated with free-space coupling into and out of a small core optical fiber. This work demonstrates that an all-fiber solution, connected only with the most basic fusion arc splicer, can be made to provide a robust, reliable, and simple tunable 2-um tunable fiber laser source. The cavity consists of a 793-nm multi-mode laser diode, which is combined with the pass-through signal in a (2+1):1 fused fiber combiner. A piece of 10/130 double clad thulium-doped fiber follows as the gain medium. An isolator follows the gain fiber to prevent feedback and force a single propagation direction in the ring cavity. A tunable Fabry Perot filter follows the isolator which allows wavelength selection based on the finesse and free-spectral range. A 90/10 fused fiber tap allows 10% of the laser power to exit, while 90% is spliced to the input port of the fused fiber pump/signal combiner. While operating in CW mode, the laser cavity demonstrates 90-nm of continuous tuning from 1970 – 2060 nm, with optical bandwidths of less than 0.05 nm with greater than 60 dB OSNR. The 90/10 output coupler allows several mW of average power to be emitted.

9728-38, Session 8

Comparison of high power large mode area and single mode 1908nm Tm-doped fiber lasers Benjamin R. Johnson, Daniel Creeden, Julia Limongelli, Herman Pretorius, Jon F. Blanchard, Scott D. Setzler, BAE Systems (United States) Most high power Tm-doped fiber lasers operate in the longer wavelength region of the emission spectrum, near 2050nm, where there are minimal re-absorption losses. The 1908nm region in Tm-doped fiber has a high emission cross-section, but it also has significant ground-state absorption, resulting in a higher overall laser threshold and reduced optical efficiency compared to operation at longer wavelengths within the thulium emission band. This three-level operation makes oscillator design critical to laser performance. Operating in the short-wavelength region of the thulium emission band is important for pumping of solid-state and fiber lasers. In this paper, we compare large mode area (LMA) and single-mode (SM) fiber geometries for use in high power 1908nm fiber lasers. With a simple endpumped geometry, we have generated 100W of 1908nm power with LMA fiber at 40% optical efficiency and 117W at 52.2% optical efficiency with a single-mode fiber. We have also power scaled both designs to the >200W power level, showing the capability for further scaling of power in this short wavelength region with high efficiency. In all cases, the fiber lasers are monotlithic, with no free-space coupling.

9728-39, Session 8

2?m single frequency fiber laser based on thulium-doped silica fiber Shijie Fu, Tianjin Univ. (China); Wei Shi, Tianjin Univ.

46

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications (China) and Tianjin Institute of Modern Laser & Optics Technology (China); Jichao Lin, Qiang Fang, Tianjin Institute of Modern Laser & Optics Technology (China); Quan Sheng, Haiwei Zhang, Tianjin Univ. (China); Jinwei Wen, Tianjin Institute of Laser Technology (China); Jianquan Yao, Tianjin Univ. (China) and Tianjin Institute of Modern Laser & Optics Technology (China) Single frequency fiber laser in 2 ?m regime has attracted intense interest recently due to the great performance in terms of low intensity noise, narrow linewidth and compactness for the applications ranging from coherent LIDAR, high-resolution spectroscopy, to nonlinear frequency conversion. The developed heavily Tm-doped germinate and silicate fibers have facilitated 2 ?m single frequency fiber lasers operating with higher output power and efficiency. However, there are still some limitations on mechanical strength and the compatibility between the active specialty fiber and passive silica fiber in the laser cavity. Fusion splicing between the highly-doped soft glass fiber and silica fiber with low-loss can be well done now, which is still challenging and requires careful handling. In this letter, we report a monolithic, DBR single frequency fiber laser at 1950 nm using a commercial Tm-doped silica fiber. The maximum output power of the single longitudinal mode laser was 18 mW and slope efficiency versus the launched pump power was 11%. Single frequency operation was confirmed by the scanning Fabry-Perot interferometer and neither mode hopping nor mode competition was observed as the pump power increased. The linewidth was measured to increase from 37 to 99 kHz when the pump power rised from 135 to 235 mW. The RIN spectra measured at different pump power showed that it was dominated by a peak at the relaxation oscillation frequency of around 500 kHz and then decreased monotonically towards higher frequencies with the RIN level of around -150 dB/Hz, which approached the shot noise limit.

wavelength soliton can be seen. The pulse width of single-wavelength soliton at 1863 nm is measured to be 3.11 ps and the repetition rate is 2.6 MHz. The tunability is based on nonlinear polarization evolution (NPE) technique. The NPE effect induces wavelength-dependent loss in the cavity to effectively alleviate mode competition and enables the multi-wavelength tunable mode locking. The wavelength tuning capabilities can be realized by controlling the polarization in the fiber ring cavity. The system provides a simple and compact solution to tunable multi-wavelength mode locking in fiber lasers. Such tunable laser has potential applications in optical signal processing and communication.

9728-15, Session PTue

Power scalability in rectangular core fiber Nan Xia, Seongwoo Yoo, Xuan Wu, Huizi Li, Nanyang Technological Univ. (Singapore) Recently, Severe modal degradation was observed in high power, rare earth doped fiber lasers and amplifiers when the pump power was above a power threshold. Many numerical models have been proposed to illustrate the cause of such mode instability, and a good method to suppress the mode instability is of highly important to high power operation area. In this paper, we utilize the beam propagation method (BPM) to numerically simulate the mode instability in a rectangular core fiber with circular cladding shape for the first time. We compare the mode instability between the rectangular core fiber and the conventional circular core fiber. Even in the circular cladding, the rectangular core can dissipate heat more efficiently than the circular core, leading to reduced mode instability. The suppression is more apparent in the high aspect ratio (AR.) rectangular core fiber as the core-cladding boundary gets closer to the edge of the cladding. Utilization of such fiber is a potential way to suppress the modal degradation in high power lasers or amplifiers.

9728-40, Session 8

Widely tunable multi-wavelength Tmdoped mode-locked fiber laser Zhiyu Yan, Nanyang Technological University (Singapore) and Singapore Institute of Manufacturing Technology (Singapore); Xiaohui Li, Nanyang Technological Univ. (Singapore); Biao Sun, Jiaqi Lou, Nanyang Technological Univ. (Singapore) and Singapore Institute of Manufacturing Technology (Singapore); Perry Ping SHUM, Nanyang Technological University (Singapore); Xia YU, Singapore Institute of Manufacturing Technology (Singapore); Ying ZHANG, SIMTech, Agency for Science, Technology and Research (Singapore); Qi Jie Wang, Nanyang Technological Univ. (Singapore) We propose and demonstrate a tunable dual- and tri- wavelength ultra-fast Tm-doped fiber laser for the first time, and the wavelength tuning range is more than 50 nm, the widest to the best of our knowledge.

9728-23, Session PTue

Compact visible through mid-IR source based on a DFB diode, fiber amplifiers, PPLN and BIBO crystals Igor V. Melnikov, National Research Univ. of Electronic Technology (Russian Federation) and Moscow Institute of Physics and Technology (Russian Federation) and Univ of Illinois at Urbana-Champaign (United States); Nikolai Balakleisky, National Research Univ of Electronic Technology (Russian Federation); Andrey A. Machnev, National Research Univ. of Electronic Technology (Russian Federation); J. Gary Eden, Univ. of Illinois at UrbanaChampaign (United States)

The fiber laser is mode-locked by nonlinear polarization evolution (NPE) technique. The setup consists of 1.5-m Tm-doped fiber as the gain medium, two polarization controllers and one isolator to induce the NPE effect, two 793 nm laser diodes with the maximum power of 170 and 200 mW as the pump source, one coupler as the output port, and 70-m single-mode fiber.

We report a compact and robust source capable of generating diffractionlimited light ranged from visible- to mid- IR (0.634-?m /1.5 – 1.7-?m / 3.4 – 3.2-?m), using a repetition–switchable single-pass PPLN and BIBO OPO architecture and, a narrow line semiconductor laser. This type of laser which integrates gain chips with a length of fiber that has a Bragg grating (BG) written in its core, has been proven to be a dense and certain source of short picoseconds to nanosecond pulses with peak power sufficient for effective parametric wavelength-tuning applications.

By increasing the pump power to 370 mW and either rotating or squeezing the PCs, dual- and tri-wavelength soliton appears. By slightly rotating or squeezing the PCs, multi-wavelength mode locking can be tuned from 1863 to 1915 nm. The fiber laser operates at soliton regime because of the typical Kelly sidebands. The separation between the two wavelengths remains around 10 nm, which is corresponded to the modulation period of cavity transmission. When decreasing the pump power to 310 mW, single-

The system is based on a narrow-line 1.064-µm 15-ns MOFA-type system as a pump source, a cw tunable fiber seed laser (1.5 – 1.6-µm), followed by a set of PPLN/BIBO-based OPGs generating pulsed 1.5 – 1.7-µm by DFG of 1.064-µm, and 0.634-µm by SFG of both 1.5- µm and 1.064-µm, correspondingly. The laser system delivers nearly diffraction-limited beams both at the visible- and mid-IR tunable wavelengths. The pulse-to-pulse energy instability does not exceed 0.1 %. Optical elements of the scheme

Return to Contents

+1 360 676 3290 · [email protected]

47

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications can be easily incorporated into the housing with footprint of 500x500x160 mm3. A variety of the undertaken measures (e.g. optimization of PPLN/BIBO lengths; temperature tuning; spectrum narrowing using the seeder; dimensions minimization, etc.) and technical treatment of the resultant device parameters make it tempting to claim this source to be a universal tool for many applications such as high-resolution spectroscopy, photomedicine, environmental control, etc.

9728-76, Session PTue

All-fiber widely tunable thulium laser Gary Stevens, Thomas H. Legg, Gooch & Housego (Torquay) Ltd. (United Kingdom) We present results from an ‘all-fibre’ thulium laser system that can be tuned to any wavelength between 1710 – 2110 nm, without using any moving mechanical parts. An Acousto-Optic Tunable Filter (AOTF) is used as the tuning element, which allows for the wavelength to be tuned in ~ 20 µs. Core-pumped and cladding pumped thulium fibres are used to allow for lasing action across the wavelength range. We use in-house fabricated fused fibre couplers and combiners that have a flattened coupling response with wavelength to allow for the system to be built in ‘all fibre’ design. These couplers have a coupling response that only varies by +/- 10% over the 400 nm operating range. The laser can output powers between 1-5 mW over 1710 – 2110nm and has a linewidth of 1MW with no sign of SRS.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications

9728-80, Session PTue

Inner cladding influence on large mode area photonic crystal fiber properties under severe heat load Enrico Coscelli, Federica Poli, Univ. degli Studi di Parma (Italy); Romain Dauliat, Univ. de Limoges (France) and Leibniz Institute of Photonic Technology (Germany) and XLIM Institut de Recherche (France); Dia Darwich, Univ. de Limoges (France) and XLIM Institut de Recherche (France) and CNRS (France); Annamaria Cucinotta, Stefano Selleri, Univ. degli Studi di Parma (Italy); Kay Schuster, LeibnizInstitut für Photonische Technologien e.V. (Germany); Aurélien Benoit, Raphael Jamier, Philippe Roy, XLIM Institut de Recherche (France) In the last years, the advantages provided by Yb-doped double-cladding Photonic Crystal Fibers (PCFs), that is very large mode area, strong pump absorption, efficient conversion and robust single-mode regime, have driven a significant development of high power fiber lasers. Currently, thermal effects represent the limit for further power scaling of fiber lasers, since they negatively affect the single-mode behavior of Large Mode Area (LMA) PCFs. In fact, beyond a certain average power threshold, unwanted energy transfer from the Fundamental Mode (FM) to the Higher-Order Modes (HOMs), originally weakly guided, occurs, causing a significant beam quality degradation. In this work, the influence of the size and the air-filling fraction of the inner cladding on the first HOM confinement in Yb-doped LMA PCFs under different heat load values has been investigated with a full-vector modal solver based on the finite element method, used also to solve the steady-state heat equation. In particular, the air-cladding inner dimension and the air-hole diameter in Symmetry-Free PCFs and Large Pitch Fibers have been modified in order to study which conditions facilitate the coupling between HOM and cladding modes, thus improving the delocalization of the former and making the fiber single-mode behavior more robust. Simulation results have shown that such coupling can be successfully exploited to suppress the HOMs when significant heat load is applied.

9728-81, Session PTue

Top hat single-mode polarization maintaining fiber and polarizing numerical design Pierre Gouriou, Lab. de Physique des Lasers, Atomes et Molécules (France) and CEA (France); Florent Scol, Commissariat à l’Énergie Atomique (France); Benoit Sevigny, Constance Valentin, Yves Quiquempois, Laurent Bigot, Rémi Habert, Andy Cassez, Olivier Vanvincq, Lab. de Physique des Lasers, Atomes et Molécules (France); Emmanuel Hugonnot, Commissariat à l’Énergie Atomique (France); Géraud Bouwmans, Lab. de Physique des Lasers, Atomes et Molécules (France) Compactness, long term stability and no free-space alignment are important advantages of fiber lasers over bulky systems. These fiber lasers have also demonstrated their capability to deliver high-power pulses and are thus suitable for numerous applications. Nevertheless the intensity profile delivered usually has a Gaussian-like shape, which most of the time is sufficient, but it could be interesting, for many applications (laserbiological tissues interactions, heat treatment, industrial laser processing or for seeding large-scale laser facilities like Laser MegaJoule) to obtain a homogeneous intensity profile at the fiber laser output. Moreover several of these applications required a linearly polarized output beam. In order

Return to Contents

to achieve all these requirements we have developed and realized a new fiber design. This fiber is the first polarization maintaining single-mode fiber delivering a flat top intensity. A high quality flat mode was obtained at 1.05µm through the use of a well-tailored index profile and single-mode behavior was verified by shifting the injection and using the S? imaging. Moreover, boron Stress Applying Parts (SAPs) including in the cladding led to a birefringence of 0.6x10-4 and a measured PER better than 20dB even for a long fiber length (~20 m). Alongside the fabrication, we developed a simulation code, using Comsol Multiphysics®, to take into account the stress dependency induced by the SAPs. Further modeling allows us to present an effectively single-mode fiber design, delivering a top-hat mode profile and exhibiting a polarizing behavior.

9728-82, Session PTue

1µm mode-locked fiber laser with tungsten disulphide absorber Yanrong Song, Heyang Guoyu, Kexuan Li, Zhiyuan Dou, Beijing Univ. of Technology (China) Abstract: Some potential applications based on passively mode-locked fiber lasers have been investigated. Recently, more effort has been concentrated on discovering and investigating new and high performance saturable absorbers(SAs) such as topological insulators (TIs), transition mental dichalcogenides (TMDs) which include molybdenum disulfide (MoS2), tungsten disulfide (WS2) and their analogue (tungsten diselenide, WSe2). Here we demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on tungsten disulphide saturable absorbers (WS2-SA). The WS2-SA were made by mixing WS2 nanosheets solution with polyvinyl alcohol (PVA), and then evaporated on a substrate. The WS2 nanosheets in the dispersion were observed by an atomic force microscope (AFM). The sizes of the WS2 nanosheets were about 150 to 300 nm and the thickness was about 4.6 nm. The modulation depth of the WS2 film was 1.78% and the saturable optical intensity was 410 MW/cm2, which were measured by a power-dependent absorption system. When the WS2 film was inserted into an Yb-doped fiber laser, the mode-locked pulses were obtained at the wavelength of 1030nm. The pulse width of 2.5 ns and a repetition rate of 2.84 MHz were reached. As the pump power increased to 350 mW, the maximum output power was ~8 mW. To the best of our knowledge, this is the first time to realize mode-locked pulses based on WS2-SA at 1?m waveband.

9728-83, Session PTue

5.5 W monolitic single-mode fiber laser and amplifier operating near 976 nm Svetlana S. Aleshkina, Mikhail E. Likhachev, Fiber Optics Research Ctr. of the Russian Academy of Sciences (Russian Federation); Denis S. Lipatov, Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (Russian Federation) and N.I. Lobachevsky State Univ. of Nizhni Novgorod (Russian Federation); Oleg I. Medvedkov, Konstantin K. Bobkov, Mikhail M. Bubnov, Fiber Optics Research Ctr. of the Russian Academy of Sciences (Russian Federation); Alexei N. Guryanov, Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (Russian Federation) In the present work we demonstrate a novel fiber design for efficient generation and amplification of laser irradiation near the wavelength of 0.98 µm. The main feature of the fiber design is an extremely low NA W-type refractive index profile (single-mode at core diameter of 28 µm) that allowed us to achieve core-to-clad diameters ratio of about 0.31. The

+1 360 676 3290 · [email protected]

49

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications photodarkening-free silica-based glass matrix was used for fabrication of the Yb-doped core. Square-shaped fibers with dimensions of 28/80x80 µm, and 40/115x115 µm coated by low-index polymer (NA=0.46) were fabricated for the laser and amplifier, correspondingly. The fiber with dimension of 28/80x80 µm was tested in a simplest all-fiber laser scheme cladding pumped by standard MM laser diode (30W at 915 nm). Output power of 5.5 W at 977 nm (limited by available pump power) was achieved in this configuration. Lasing threshold and slope efficiency were 10 W and 25%, correspondingly. The fiber with dimension of 40/115x115 µm was used for building an all-fiber amplifier scheme. The fabricated fiber was spliced with a standard pumpand-signal combiner, seeded by standard semiconductor laser diode with power of 100 mW at 976nm and pumped by two multimode diodes with net power of 60 W. The maximum output power of 5.7 W was achieved. The slope efficiency was about 15%.

9728-84, Session PTue

Experimental investigation of pedestal suppression in a figure-eight fiber laser by including a polarization asymmetrical NOLM Migel A. Bello-Jimenez, Erika Hernández-Escobar, Instituto de Investigación en Comunicación Òptica (Mexico); Evgeny A. Kuzin, Baldemar Ibarra-Escamilla, Manuel Durán-Sánchez, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico); Antonio Diez Cremades, Jose L. Cruz, Miguel V. Andrés, Univ. de València (Spain) A polarization asymmetrical nonlinear optical loop mirror (NOLM) is investigated to perform pedestal-free optical pulses in a figure-eight laser (F8L). The NOLM is composed of a symmetrical coupler, with output ports connected to 220 m of twisted fiber, and a quarter wave retarder (QWR) located asymmetrically into the loop. In the low-intensity regime the NOLM shows a periodical dependence on the QWR angle, with a minimal and maximal transmission equal to 0 and 0.5, respectively. The power-dependent transmission is investigated for each circular polarization component at the NOLM output, considering a right circular input polarization, and the dependence on the QWR angle. The results demonstrate that in the low-power regime the NOLM operates as a halfwave plate and the output polarization is orthogonal to the input one. However, at higher power level the polarization component parallel to the input appears, with a transmission that always begins from zero at low power, allowing the rejection of low-intensity components. This property results very attractive to perform modelocked operation in a F8L. The low-intensity component, with polarization orthogonal to the input, can be implemented to initiate the modelocking process, whereas the parallel component can be associated to high-intensity optical pulses with zero transmission for low-intensity compoments. This configuration allows the generation of optical pulses with peak power close to the maximum peak power value obtainable from the average output power. Experimental results demonstrate that by employing this configuration we can obtain a contrast between the peak and continuous background higher that 30 dB.

9728-85, Session PTue

Single-frequency Raman fiber amplifier emitting 11 µj 150 W peak-power at 1645 nm for remote methane sensing applications Philippe Benoit, Nicolas Cézard, Anne Durécu, ONERA (France); Arnaud Mussot, Lab. de Physique des Lasers,

50

Atomes et Molécules (France) and IRCICA (France); Alexandre Kudlinski, Univ. des Sciences et Technologies de Lille (France) and IRCICA (France); Guillaume Canat, ONERA (France) Remote methane concentration measurement using a Differential Absorption Lidar system can be performed using a single-frequency pulsed laser source at 1645.55 nm. This wavelength cannot be efficiently amplified in conventional Erbium Doped Fiber Amplifier as the gain band stops around 1620 nm. We report on a single-frequency polarization-maintaining pulsed amplifier at 1645 nm relying on stimulated Raman scattering (SRS) in highly nonlinear silica fibers (HNLF). Considering that SRS converts pump photons to photons frequency-downshifted by 13.2 THz with a gain bandwidth of 2 THz, a 1545 nm pump can efficiently amplify a 1645 nm seed laser. The drawback of using a HNLF is that the single-frequency signal will also experience stimulated Brillouin scattering (SBS) through its amplification. This issue has been partially solved by designing a two-stage amplification setup minimizing SBS. In the first stage, a 20 m piece of HNLF has been used so that the effective length of the amplified signal stays under SBS threshold. In the second stage, we used a 2.5 m piece of HNLF and high pump peak-power to significantly reduce the effective length, allowing more amplification. We report on generation of single-frequency 11 µJ energy pulses at 1645 nm corresponding to 150 W peak-power and 80 ns pulse duration at 20 kHz pulse repetition frequency.

9728-86, Session PTue

Pulsed interferometric phase measurement for coherent beam combining Jeremy Le Dortz, Thales Research & Technology (France); Marie Antier, Thales Optronique S.A.S. (France); Jérôme Bourderionnet, Christian Larat, Eric Lallier, Thales Research & Technology (France); Louis Daniault, Severine Bellanger, Lab. pour l’Utilisation des Lasers Intenses (France) and Ecole Polytechnique (France); Christophe Simon-Boisson, Thales Optronique S.A.S. (France); Jean-Christophe F. Chanteloup, Ecole Polytechnique (France) and Lab. pour l’Utilisation des Lasers Intenses (France); Arnaud Brignon, Thales Research & Technology (France) Coherent beam combining (CBC) of fiber amplifiers provides an attractive mean of reaching high peak and high average powers. Active CBC techniques involve phase detection and compensation of the phase variations of each amplifier. Interferometric phase measurement has proven to be particularly well suited to phase-lock a large number of fibers in continuous regime. In this presentation, we demonstrate for the first time the phase locking of three fibers in femtosecond pulse regime with this technique. A master oscillator generates pulses of 300fs (chirped at 200ps). The beam is split into four channels. Phase locking is implemented on three fibers with respect to the fourth, acting as a phase reference. Prior to phase locking, the optical path differences are adjusted. Interferograms for the three fibers are recorded at 1kHz with a camera. A dedicated algorithm is developed to measure both the phase and the delay between the fibers. The delay and phase shift are thus calculated collectively from a single image and piezoelectric fiber stretchers are controlled in order to ensure compensation of time-varying phase and delay variations. The measured phase shift errors between the fibers are below ?/80rms when the servo-loop is operating. Phase noise power spectral densities of a fiber amplifier operating in the short pulse regime will be also presented in opened and closed loop to assess the bandwidth of the control loop and the capability of our locking technique to perform CBC of fiber amplifiers operating in the short pulse regime.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications

9728-87, Session PTue

Statistical model of the energy transfer in Er3+:Yb3+-codoped glasses Michael Steinke, Jörg Neumann, Dietmar Kracht, Peter Wessels, Laser Zentrum Hannover e.V. (Germany) A novel statistical model for the energy transfer process in Er3+:Yb3+codoped glasses, e.g. fibers, is presented. The model is based on an existing stochastic model for the homogeneous up-conversion in Er3+-doped glasses and the most important advantage is the correct modeling of the energy transfer as a dipole-dipole interaction. Thus, the model avoids the unreasonable but common modeling of the Er3+-to-Yb3+ energy transfer as a fixed rate which is simply multiplied with the upper Yb3+ state population and the ground state Er3+ population. Exemplary results obtained with the novel statistical model behave reasonable, i.e. the population densities of the Yb3+ and Er3+ upper states depend on the individual parameters of the model as expected. Therefore, the presented model provides good prospects to study optimization strategies of Er3+:Yb3+-codoped fibers. Furthermore, the model can be further developed and expanded in the future, e.g. by including energy migration amongst the individual Yb3+-ions and Er3+-ions.

9728-90, Session PTue

Passive mode locking through nonlinear coupling with different dual-core fiber length Xiaohui Fang, Beijing Univ. of Technology (China)

9728-88, Session PTue

Experimental study of a linear cavity dual wavelength Er/Yb double clad fiber laser operating in self-Q-switch, self-pulsing and CW Manuel Durán-Sánchez, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico) and Cátedras CONACyT (Mexico); Ricardo I. Álvarez-Tamayo, Univ. Tecnológica de Puebla (Mexico); Olivier J. M. Pottiez, Ctr. de Investigaciones en Óptica, A.C. (Mexico); Berenice PosadaRamírez, Baldemar Ibarra-Escamilla, Evgeny A. Kuzin, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico); Antonio Barcelata-Pinzón, Univ. Tecnológica de Puebla (Mexico) We present experimental results of a proposed dual wavelength fiber laser with Er/Yb double clad fiber. With pump power variations the laser to 1 W Self-Q-switched pulses are obtained. With a pump power range from 1 W to 2 W, self-pulsing operation is observed. With pump power above 2 W CW operation is achieved. The linear cavity laser is based in the use of two fiber Bragg gratings for wavelength selection and a Sagnac interferometer for cavity losses adjustment to obtain dual-wavelength operation. Power efficiency is around 36%. In self-Q-switch operation maximal repetition rate is 60kHz with pulse duration in micro seconds range. With pump power of 10 W, the maximal average output power of 3.6 W is obtained for CW operation.

9728-89, Session PTue

Dual-comb spectroscopy with a freerunning bidirectionally mode-locked fiber laser Khanh Q. Kieu, Seyed Soroush Mehravar, Robert A. Norwood, Nasser N. Peyghambarian, College of Optical Sciences, The Univ. of Arizona (United States) Dual-comb technique has enabled exciting applications in high resolution optical spectroscopy, precision distance measurements, and 3D imaging.

Return to Contents

Major advantages over traditional methods for these applications can be achieved with dual-comb technique. For example, dual-comb spectroscopy provides orders of magnitude improvement in acquisition speed over standard Fourier-transform spectroscopy while still preserving the high resolution capability. Wider adoption of the technique has, however, been hindered by the need for complex and expensive ultrafast laser systems. Here, we present a simple and robust dual-comb technique that employs a free-running bidirectionally mode-locked fiber laser operating at telecommunication wavelength. Two femtosecond frequency combs (with a small difference in repetition rates) are generated from a single laser cavity to ensure mutual coherent properties and common noise cancellation. We demonstrate real-time absorption spectroscopy measurements without the need for complex servo locking or adaptive sampling with accurate frequency referencing and relatively high signal-to-noise ratio. The compact and all-fiber implementation scheme makes this technique a promising tool for practical, outside-of-laboratory applications.

The effect of fiber length on ultrafast pulse formation in active dual-core fiber laser is investigated numerically, which has been ignored in previews studies. The simulation results show that stable self-starting mode-locked operation can be realized with a dual-core fiber length shorter than the linear coupling length. A filter is necessary to stabilize mode-locking operation when the fiber length is longer than the linear coupling length. And mode-locking operation can not be self-started from noise with a fiber length equal to the linear coupling length.

9728-91, Session PTue

Characterization technique for long optical fiber cavities based on beating spectrum of multi-longitudinal mode fiber laser and beating spectrum in the RF domain George A. Adib, Yasser M. Sabry, Diaa A. Khalil, Ain Shams Univ. (Egypt) Optical fiber cavities are basic building blocks in different applications including fiber laser, fiber-laser frequency combs,swept laser source, environmental and rotation sensors. For many applications, the cavity length is needed to be relatively long- in the order of meters or kilometersto achieve a fine 3-dB bandwidth and free spectral range stability. The characterization of long fiber cavities is, thus, essential to design these systems and predict their practical performance.The conventional techniques for optical cavity characterization are not suitable for long fiber cavities due to the cavities’ small free spectral ranges and due to the wavelength instability (length variations) caused by the environmental effects.In this work, we present a novel technique to characterize long fiber cavities using multi-longitudinal mode fiber laser source and RF spectrum analyzer. The output of the laser is used as an input to the cavity under test. The output of the cavity is fed to a square-law optical detector and its electrical output is recorded on the RF spectrum analyzer. Then, the RF spectrum is used to obtain the response of the cavity. The method has been applied experimentally to characterize ring cavities with lengths of 6 m and 2.4 km. The fiber laser source is formed in a ring configuration, where the fiber laser cavity length is chosen to be 15 km to ensure the free spectral range is much smaller than the free spectral range of the characterized passive fiber cavities. The results are compared to theoretical predictions with very good agreement.

+1 360 676 3290 · [email protected]

51

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications

9728-92, Session PTue

9728-94, Session PTue

Modelocked, Q-switched, or Q-switched modelocked operation of a fiber oscillator by adjusting the mode-field area within the graphene oxide saturable absorber

Broadband wavelength tuning of hybrid femtosecond Er/Tm fiber laser system in microstructured suspended-core tellurite fiber

Manuel Ryser, Alexander M. Heidt, Thomas Feurer, Valerio Romano, Univ. Bern (Switzerland)

Maksim Y. Koptev, Institute of Applied Physics of the RAS (Russian Federation); Elena A. Anashkina, Institute of Applied Physics of the RAS (Russian Federation) and N.I. Lobachevsky State Univ. of Nizhni Novgorod (Russian Federation); Alexey V. Andrianov, Institute of Applied Physics of the RAS (Russian Federation); Vitaly V. Dorofeev, Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (Russian Federation); Alexey F. Kosolapov, Fiber Optics Research Ctr. of the Russian Academy of Sciences (Russian Federation); Sergey V. Muravyev, Institute of Applied Physics of the RAS (Russian Federation); Arkady V. Kim, Institute of Applied Physics of the RAS (Russian Federation) and N.I. Lobachevsky State Univ. of Nizhni Novgorod (Russian Federation)

We have demonstrated a fiber ring oscillator in modelocking, Q-switching and simultaneous Q- switched modelocking operation mode at constant pump power level. The different oscillation states of the cavity were reached by varying the mode-field area within the graphene oxide saturable absorber (GO-SA) and not as commonly done by adjusting the optical pump power. All fibers and fiber coupled elements used in our setup are polarization maintaining. Thus, the only available mode-locking mechanism in this fiber ring oscillator is the saturable aborption at the GO-SA and mode-locking based on nonlinear polarization rotation can be excluded. Widely used methods for producing ultrashort pulses in laser cavities are Q- switching and modelocking. Q-switching allows the generation of milli-joule pulses with microsecond to nanosecond duration and hertz to many kilohertz repetition rates. Mode-locking produces typically picojoule to nano-joule pulses with femto- to picosecond pulse durations and megahertz to gigahertz repetition rates. Furthermore, a laser cavity can also operate simultaneously in Q-switched and modelocking regime to produce a pulse train at MHz with a modulation envelope at kHz repetition rate. The Q-switched modelocked pulses are modulated in amplitude the most intense pulses can reach energies several times higher than would be possible with pure modelocking. With the approach presented here various operation modes can be achieved at the same pump power level, which gives great flexibility in generating ultrashort optical pulses over a broad range of durations, repetition rates and energies from the same laser cavity.

9728-93, Session PTue

Switchable dual-pulse-shape mode-locked figure-eight all-PM fibre master oscillator with 0.5 W-level average output Sergey M. Kobtsev, Aleksey V. Ivanenko, Yurii Fedotov, Sergey V. Smirnov, Novosibirsk State Univ. (Russian Federation); Artur Golubtsov, Sergey Khripunov, Novosibirsk State Univ (Russian Federation) For the first time a method for switching between generation of single- and double-scale pulses has been demonstrated in a mode-locked figureeight NALM-based all-PM-fibre Yb master oscillator by adjustment of two pumps power. Introduction into a F8 configuration of a non-linear amplifying loop mirror with two active media not only ensured relatively high average output power of the master oscillator (> 0.5 W at 22-MHz repetition rate), but also allowed switching laser operation from one pulse type (single-scale coherent pulses with duration of < 10 ps) to another femtosecond clusters with envelope width of 16 ps and sub-pulse duration < 200 fs. Implementation of an all-PM-fibre configuration dispensed with the requirement of polarisation controllers (they were used in the previous configuration of this master oscillator) and to trigger mode-locked operation by selection of power levels of the two pump sources. The suggested optical layout features output via two ports. A larger portion of the radiation exited the master oscillator through port 1 at the average output power of 600 mW for single-scale pulses and 525 mW for femtosecond clusters (double-scale pulses). The average power of radiation exiting through port 2 amounted to 140 and 280 mW correspondingly. The proposed method of switching between generation of single-scale and double-scale pulses by adjustment of relative levels of two pump sources provides considerably faster and more reproducible regime switching in comparison to switching by adjustment of polarisation controllers.

52

We propose a widely tunable in the 1.6-2.6 ?m range femtosecond fiber laser source, generating high-quality sech-shaped pulses with the duration of the order of 100 fs. The source contains an all-fiber hybrid Er/ Tm femtosecond laser system that generates 2 nJ 150 fs pulses in Erbium channel and 4 nJ 125 fs pulses in Thulium channel. The laser was coupled to a piece of suspended-core microstructured TeO2-WO3-La2O3 glass fiber with 3.2 ?m core diameter and ZDW of approximately 1.5 ?m. We experimentally obtained tunable high-quality Raman solitons up to 2.25 and 2.6 ?m with the pump at 1.6 and 2 ?m, respectively. Their spectral widths correspond to the Fourier transform-limited duration of about 100 fs. We have also made theoretical studies of self-frequency soliton shifting in the tellurite fiber with carefully measured and calculated parameters, based on the one-way wave equation dealing with the full electric field of light. Our numerical model is in a very good agreement with the experiment and also shows Raman soliton self-frequency shift in the range well beyond 3 ?m for increased pump energy. So, the demonstrated turnkey fiber-based laser source can be used for applications requiring high-quality ultrabroadband femtosecond optical pulses.

9728-95, Session PTue

Tunable pulse width and multi-megawatt peak-power pulses from a nonlinearly compressed monolithic fiber MOPA system Ryutarou Yamashita, Kazuo Maeda, Goro Watanabe, Kazuyoku Tei, Shigeru Yamaguchi, Tokai Univ. (Japan); Jun Enokidani, Shin Sumida, OPT-i Co., Ltd (Japan) We report on tunable pulse width and energetic pulse generation from a nonlinearly compressed monolithic fiber MOPA system. The master seed source employs a Mach-Zehnder intensity modulator (MZIM). This seed source has operational flexibility with respect to pulse width, 90 ps to 2 ns and repetition rate, 200 kHz to 2 MHz. The seed pulses are amplified by a monolithic three-stage amplifier system based on polarization maintain Yb-doped fibers. The maximum output power was 32 W at the shortest pulse condition, the pulse width of 90 ps and repetition rate of 2 MHz. A spectral width after amplification was broadened to 0.65 nm at RMS width. Both of ASE and SRS are not observed in the spectrum. After amplification, we also demonstrated pulse compression with a small piece of chirpedvolume-bragg-grating (CVBG) which has the dispersion rate of 81 ps/nm. As a result of pulse compression, the shortest pulse width was reduced from

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications 90 ps to 4 ps, which brought an increase of the peak power up to 2.9 MW. The autocorrelation traces are well matched with the Gaussian function. The compressed pulses are clean with very little structure in there wings. We can expand the operation range of the monolithic-fiber MOPA system in pulse width, 4 ps to 2 ns.

9728-96, Session PTue

Fabrication and investigation of active composite fibers with phosphate core and silica cladding Sergey L. Semjonov, Olga N. Egorova, Oleg I. Medvedkov, Maxim S. Astapovich, Andrey G. Okhrimchuk, Evgeny M. Dianov, Fiber Optics Research Ctr. of the Russian Academy of Sciences (Russian Federation); Boris I. Denker, Boris I. Galagan, A. M. Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation); Sergey E. Sverchkov, A. M. Prokhorov General Physics Institute (Russian Federation) Phosphate glass is a unique host for lanthanide ion doping: high concentrations of rare earth (RE) ions can be incorporated into phosphate glass, the phosphate glass host provides efficient and irreversible energy transfer from Yb3+ ions to Er3+. Additionally, Yb-doped phosphate glass is highly resistant against photodarkening even at high Yb3+ concentration. High doping levels of phosphate fibers make it possible to obtain high gain and high output power per unit length, thus reducing the length of active fibers in comparison to silica based fibers. A substantial drawback of the use of phosphate glasses as a material for fiber fabrication in comparison with silica is their low stability; exposure to air moisture causes degradation of the phosphate fibers over time. Moreover, due to the sharp difference in their physical properties, splicing of phosphate and silica fibers is difficult. In this presentation, we describe composite optical fibers with rare-earth co-doped phosphate-glass core in a silica-glass cladding. High RE-ion concentrations in the phosphate core of the composite fiber allow fiber length reduction in comparison with silica fibers. The silica cladding provides high mechanical strength and protects the phosphate core from air moisture while making it easier to splice with silica fibers. Both fabrication of fibers and their optical properties will be discussed. The lasing efficiency of the composite fibers was found to be high in both cases - cladding and core pumping.

9728-97, Session PTue

Controlled generation of optical rogue waves in dispersion oscillating fiber Alexey Sysoliatin, Konstantin Gochelashvili, A. M. Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation); Andrey I. Konyukhov, N.G. Chernyshevsky Saratov State Univ. (Russian Federation); Leonid A. Melnikov, Saratov State Technical Univ. (Russian Federation); Mikhail Y. Salganskii, Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (Russian Federation) Generation of high-intensity rogue waves from optical turbulence or breathers is considered usually as statistically-rare process [J.M. Dudley et al. Nature Photonics 8, 755 (2014)]. We propose a new approach for the generation of separated optical rogue waves “on demand”. The proposed scheme utilizes dispersion oscillating fiber. Variation of the fiber dispersion can be made during its drawing process [A.A. Sysoliatin et al. Opt. Expr.

Return to Contents

25, 16302 (2007)]. Using numerical simulation the solitons collision and merge of solitons in dispersion oscillating fiber are considered. Rogue wave arises as result of the inelastic collision of optical solitons. Inelastic collisions are forced by periodical variation of the fiber dispersion. Due to inelastic interactions, the solitons merge together and give birth to a new soliton whose amplitude is significantly greater than the amplitude of the other satellite solitons. After the merging process, the dynamics of the output pulse is determined mainly by a single high-amplitude soliton called as rogue wave. The parameters of the rogue wave depends on the modulation period of the fiber diameter, repetition rate of the host laser. The generation of single high-amplitude soliton can be actively controlled via chirp of input pulses. The generation of the rogue waves both in active and passive dispersion oscillating fibers is considered.

9728-98, Session PTue

Broadband optical amplification with water-free hexagonal double-clad Bi doped silica fiber Soichi Kobayashi, Mikoto Takahashi, Mizuki Ohara, Ikki Kondo, Chitose Institute of Science and Technology (Japan); Yusuke Fujii, Photonic Science Technology, Inc. (Japan) 1.3 - 1.55 ?m optical amplifiers for the long distance up-stream and down-stream networks for a future increase of fiber access network in telecommunications are attractive. A bismuth-doped silica glass has a potential of the broadband spectrum as laser and amplifier applications at 1.3 -1.55 ?m. The bismuth-doped fiber lasers and amplifiers were discussed by the Dianov group fabricating by the MOCVD method. In this report optical amplification characteristics at 1.3 - 1.55 ?m are presented with the water free hexagonal double-clad bismuth-doped silica fiber (HDC-BDF) made by the VAD method. The bismuth and aluminum ions were vapor– ?phase doped into the silicon and germanium oxide. The concentration of Bi oxide in the core glass was measured as 0.8 wt% by EDX spectroscopy. Refractive index difference between the core and the first cladding in the preform was measured as 0.5 % by the optical fiber preform analyzer. The hexagonal preform was drawn into the fiber where the core and the first cladding diameters were measured as 7 ?m and 100 ?m between flat surfaces, respectively. The relative refractive index difference between the silica first-cladding and the polymer first-cladding is 3.6%. Pumping into the HDC-BDF was performed by using the 15 degree tilt-polished fiber from the hexagonal surface with the multimode fiber pigtail of the pumping LD. In the case of the hexagonal fiber it is easy to realize a perfect splicing with the single-mode fiber. 1 dB/m amplification in 1310 nm was measured with 4 m long HDC-BDF where SNR is over 35 dB with -40 dBm input signal.

9728-99, Session PTue

A diode drive mechanism for always resonant pumping with laser diodes without wavelength locking S. Arun, Ctr. for Nano Science and Engineering (CeNSE) (India) and Indian Institute of Science (India); Balaswamy Velpula, Indian Institute of Science (India) and Ctr. for Nano Science and Engineering (India); Great Chayran, Indian Institute of Science (India); P. Vanitha, Abhishek Kumar, V. R. Supradeepa, Indian Institute of Science (India) and Ctr. for Nano Science and Engineering (India) An essential requirement in lasers and amplifiers utilizing a rare-earth doped gain medium is to have substantial match between the emission wavelengths of the pump laser diodes to the absorption band of the gain medium. This would enable the optimal balance of laser efficiency

+1 360 676 3290 · [email protected]

53

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications and nonlinearity. Further, this leads to improved system reliability - by minimizing issues arising from unabsorbed pump and cost - by minimizing the length of gain media. However, the emission wavelengths vary as a function of various parameters, primarily output power (drive current), temperature and variation in device parameters. The latter two factors can be easily overcome through the choice of proper heat-sink temperatures and by using diodes binned according to their emission wavelength. However, a fundamental limitation is the variation of emission wavelength as a function of output power (drive current). Currently, the alternative is to use wavelength locked laser diodes. This comes at the cost of reduced efficiency and/or enhanced price owing to additional components and packaging necessary in each module. In this work, we demonstrate a novel drive scheme for standard laser diode modules without wavelength locking. This scheme enables “alwaysresonant” pumping by the diodes. The deleterious effect of emission wavelength drift accompanying power tuning, is completely avoided. In this work, we demonstrate the drive mechanism and its performance in a fiber amplifier configuration. We anticipate this scheme to have significant impact in enabling a cost-effective solution which achieves an optimal balance of efficiency, nonlinearity and reliability in laser systems.

electrically tunable all-fiber graphene device with high efficiency based on strongly enhanced graphene-evanescent wave interaction. We successfully fabricated a graphene-based field effect transistor on a side-polished fiber mediated by an ion-liquid. Gate-variable electrical transport and related optical properties are simultaneously studied as a function of number of graphene sheet, which reveals that it exhibits non-resonant large optical transition change (> 90%) for applied voltage of less than 3 V. Taking the advantages of all-fiber device with high optical damage threshold, the proposed device is successfully integrated into all-fiber laser system as an electrically tunable in-line graphene saturable absorber. We observed that nonlinear saturable absorption properties of our all-fiber graphene device can be tuned as we adjust the applied electrical signal. This subsequently modifies the laser cavity condition, enabling gate-controlled pulsed fiber laser operation at various operation regimes including continuous wave mode-locking and Q-switching. Further possible applications of the proposed device for tunable nonlinear optic signal generation, fine control of passively mode-locked fiber laser, and broadband optoelectronic devices will be also discussed based on our all-fiber graphene devices with enhanced device efficiency.

9728-102, Session PTue

9728-100, Session PTue

Understanding gain saturation: a pseudo intensity limiter in pulsed fiber amplifiers

High power, high signal-to-noise ratio single-frequency 1 ?m Brillouin all-fiber laser

Nishant K. Shekhar, Sourav Das Chowdhury, Ranjan Sen, Mrinmay Pal, Central Glass and Ceramic Research Institute (India)

Jing Wang, Yubin Hou, Qian Zhang, Dongchen Jin, Ruoyu Sun, Hongxing Shi, Jiang Liu, Pu Wang, Beijing Univ. of Technology (China)

In the process of development of high energy nanosecond pulsed fiber lasers, we confronted a phenomenon that manifested itself as an intensity limiter much like the non-linear scatterings, namely SBS and SRS. The phenomenon was coined ‘Gain Saturation’ in laser literature, notorious for its distorting ability of square shaped pulses. But its intensity limiting behavior was accentuated only when a 100ns width Gaussian pulse was unable to get amplified over 2 KW of peak power. Higher pumping only led to broadening of the pulse to 120ns without enhancement of its peak power. A numerical simulation was done so as to mimic the occurrence of gain saturation. Initially the numerical model predicted a higher intensity achievable than what was measured in the experiment. This mismatch of numerical prediction and experimental observation was later corrected by incorporating the effect of ‘Numerical Aperture’ of the fiber. The numerical simulation combined with experimental observation led to an empirical relation between fiber parameters, fiber material and the maximum intensity that could be achieved for a Gaussian pulse of constant width before gain saturation appeared. Based on the empirical relational, a fiber with required dimension was fabricated which later in a table top experiment attained the desired peak power combined with high energy. Simultaneously, a fluid analogy was also devised in order to explain in an alternate way the happening of ‘Gain Saturation’. The fluid analogy also helped in simplifying the complexities of “Gain Saturation’.

We have demonstrated a high power, high-optical signal-to-noise ratio (OSNR) single-frequency 1 ?m Brillouin all-fiber laser. The Brillouin fiber laser (BFL) consists of a continuous-wave Yb-doped single-frequency seed source, one-stage Yb-doped fiber amplifier (YDFA) pumped by fiberpigtailed multimode laser diode and a single-pass Brillouin ring cavity. The seed source is a homemade short-linear-cavity distributed Bragg reflector (DBR) single-frequency fiber laser with the output power of 35 mW and the linewidth of 20 kHz. Through one-stage YDFA, the seed laser is amplified to 2.615 W limited by the optical power of the isolator. The laser is then split into two unequal parts with 99/1 fiber coupler and the output from 99% coupler is served as the Brillouin pump (BP) with 2.588 W output power, which is injected into the single-pass Brillouin ring cavity. By optimizing the length of the cavity to 10m, stable single-longitudinal-mode operation is obtained with 2 kHz linewidth owing to the linewidth narrowing effect. The single-frequency BFL generates an average output power of 1.402 W at 2.588 W pump power with 70% output coupler. The laser does not show any phenomena of saturation, so more output power is expected if a higher power pump laser is launched. The slope efficiency is 79% considering the loss of the circulator. The OSNR of the BFL in the maximum output power is 77 dB which can be 27 dB better than the BP owing to the intensity and phase-noise reduction of the SBS process.

9728-103, Session PTue

9728-101, Session PTue

Electrically tunable in-line graphene saturable absorber for pulsed fiber laser applications Dong-Il Yeom, Ajou Univ. (Korea, Republic of) Active control of light in an optical fiber has been studied with great interest due to its compatibility with diverse fiber-optic communication and fiber laser systems. Although the optical absorption properties of graphene can be modified through the Fermi-level control in a graphene layer by applied electrical signal, realization of gate-controlled graphene device in an optical fiber platform remains highly challenging. In this presentation, we report an

54

Yb-doped large mode area fibers with depressed clad and dopant confinement Vincent Roy, Claude Paré, Pierre Laperle, Louis Desbiens, Yves Taillon, INO (Canada) Large mode area (LMA) fibers with depressed-index cladding layer and confinement of rare-earth dopants can provide effective suppression of high-order modes (HOMs). The latter favors preferential amplification of the fundamental mode through optimized differential in mode overlap with rare-earth dopants whereas the former results in increased differential bending losses as a result of the lower effective numerical aperture seen by HOMs. Both of these methods are shown herein to be quite effective at

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications suppressing HOMs for fibers with large core diameters when implemented together. A polarization-maintaining Yb-doped double-clad fiber with 35/250 µm core/clad diameter has been fabricated from conventional MCVD and solution doping process according to this design. The fiber which has an effective fundamental mode area close to 500 µm2 yields near diffractionlimited output with beam quality factor M2 close to 1.1 when tested as a power amplifier with a 1064 nm coherent seed light source. The exceptional beam quality is maintained for high power, well over 20dB of gain. Beam pointing measurements provide additional evidence for near single-mode behavior as the pointing fluctuations are shown to be negligible. Besides, the beam characteristics are further examined for coupling conditions that yield a significant fraction of energy into HOMs in order to show how effective is the suppression of these modes. We are confident for the effective mode area of the LMA fiber design proposed herein to be readily scalable over 1000 µm2 and yet allow for reasonably good beam quality.

9728-104, Session PTue

provided an error signal for active phase stabilization which was performed via Locking of Optical Coherence by Single-Detector Electronic-Frequency Tagging (LOCSET).After phase stabilization, the beams were coherently combined via the 1x5 DOE. A total combined output power of 5 kW was achieved with 82% combining efficiency. The intrinsic DOE splitter loss was 5%. Similarly, the losses due to non-ideal polarization extinction were 2.5%. Other losses include residual phase error control (1-2%), amplifier amplified spontaneous emission (ASE), and largely, fractional beam displacement and misalignment errors. Near diffraction-limited beam quality at 5 kW was attained with a measured M2 value of 1.06.

9728-106, Session PTue

Linewidth investigation of high-power single-frequency Tm-doped fiber amplifier Haiwei Zhang, Wei Shi, Quan Sheng, Tianjin Univ. (China)

Simultaneous mode and nonlinearfrequency conversion of HOMs Oleg Shatrovoy, Boston Univ. (United States); Siddharth Ramachandran, Lars Rishoj, The Boston Univ. Photonics Ctr. (United States) We present a simulated device that performs efficient (90%) secondharmonic generation (SHG) of a truncated Bessel beam that mirrors higher order modes (HOM) of fibers, while simultaneously converting it to a Gaussian-like spatial profile. The simulations reveal that a 1064-nm 250-W truncated Bessel beam with 9 rings, mirroring the profile of an LP0,10 mode, under noncollinear phase matching conditions, converts into a 225-W beam with primarily a central spot. The central spot has 93% of its power within a 5mrad divergence angle and a 70% overlap with a perfect Gaussian beam. The simulated results reveal two attractive features – the feasibility of efficiently converting HOMs of fibers into Gaussian-like beams, and the ability to simultaneously perform frequency conversion, which may have applications in realizing high-power sources in non-traditional colors. The split-step method was used to alternatingly apply the solutions of the linear and nonlinear parts of the differential equations describing the second-harmonic interaction with diffraction over a small propagation steps. Beam input power and phase mismatch for optimal output were chosen by performing a parameter sweep of those variables.

9728-105, Session PTue

Multi-kW coherent combining of fiber lasers seeded with pseudo random phase modulated light

We analyse the linewidth characteristic of a high-power single-frequency Tm-doped fiber amplifier (TDFA) with the power up to 45 W for the first time. The Lorentzian line shape 3dB linewidth of the output signal is ~56 kHz at the maximum power. Moreover, the linewidth of the output laser with different power is measured via the delayed self-heterodyne method. The experimental results indicate that the Lorentzian line shape linewidth decreases firstly and then increases later with the increase of output signal power. It shows that the Lorentzian linewidth of high-power single-frequency TDFA increases with the increment of the amplifier gain factor. However, with the increase of pump power, the broadening of the laser linewidth is due to the increase of the in-band amplified stimulated emission, which can reduce the amplifier gain factor.

9728-107, Session PTue

2 µm ultrafast fiber laser modelocked by mechanically exfoliated Sb2Te3 Jan Tarka, Jakub Boguslawski, Maciej Kowalczyk, Grzegorz J. Sobon, Jaroslaw Z. Sotor, Wroclaw Univ. of Technology (Poland) We demonstrate the usage of a new saturable absorber material -antimony telluride (Sb2Te3) for efficient mode-locking of an Thulium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber ferrule. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 4.5 nm centered at 1945 nm, with 39.5 MHz repetition rate and more than 60 dB signal to noise ratio. The pulse energy of the generated 850 fs pulses was at the level of 30 pJ.

Angel Flores, Air Force Research Lab. (United States); Thomas Ehrehreich, Roger H. Holten, Leidos, Inc. (United States); Iyad Dajani, Air Force Research Lab. (United States)

9728-109, Session PTue

Recently, we have shown that assuming an optimal pattern is chosen, pseudo-random bit sequence (PRBS) phase modulation provides superior SBS suppression to that provided by white noise source (WNS) for a given fiber length and signal linewidth. Furthermore, we successfully demonstrated coherent beam combining (CBC) of two 150W PRBS phase modulated fiber amplifiers. In this work, we demonstrate CBC of five path length-matched 1.2 kW fiber amplifiers with a diffractive optical element (DOE) and report a combined output power of 5 kW. Each non polarization-maintaining fiber amplifier provides approximately 1.2-1.3 kW of near diffraction-limited output power (M2~1.1). A low power sample of each laser was utilized for active polarization control. After polarization locking, polarization extinction ratios (PER) of 15-16 dB were measured for each amplifier. A low power sample of the combined beam after the DOE

Xiaosheng Huang, Seongwoo Yoo, Ken Tye Yong, Nanyang Technological Univ. (Singapore); Feng Luan, Shenzhen University (China); Wenliang Qi, Daryl Ho, Nanyang Technological Univ. (Singapore)

Return to Contents

Hollow core anti-resonant fibres with split cladding

An improved design for hollow-core inhibited coupling fibres (HC-ICFs) is presented. It consists of eliminating asymmetric part of the core-cladding boundary of a hollow inhibited coupling fibre and has a fibre structure with split cladding (SCF). The SCF has desirable properties such as a symmetric and discontinuous core-cladding boundary which help to reduce the structure deformation in fabrication process. In addition, the discontinuous core-cladding boundary can avoid the high loss introduced by

+1 360 676 3290 · [email protected]

55

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications the touching areas between capillaries. The negative curvature also can be easily achieved in this fibre design even without the pressure control during fabrication process. Simulation results are presented to compare the confinement loss of : conventional hollow inhibited coupling fibre (HIF) and SCF. Overall the leakage losses of HIF and SCF are in the same level and both have the potential to have lower background loss than the telecom fibres. However, the structure like HIF is more likely to suffer a core shape deformation since its core-cladding boundary is asymmetric and continuous. The relationship between confinement loss and tube pitch amplification coefficient, g, has been studied and a confinement loss lower than 0.01dB/ km can be achieved by controlling the pitch amplification coefficient. The fabricated SCF shows promising results with insignificant deformation, and the measured transmission is consistent with the simulation result.

9728-110, Session PTue

Dependence of photodarkening under different wavelength pumping Huizi Li, Seongwoo Yoo, Sidharthan Raghuraman, Daryl Ho, Xuan Wu, Tianye Huang, Nanyang Technological Univ. (Singapore) A photodarkening (PD) effect in ytterbium (Yb)-doped fiber is dependent on the number of excited ions in the upper level of Yb ion. However, the dependence of pumping wavelengths has been overlooked. In our work, we show that the PD is not only dependent of the population inversion level but also the pump wavelength. We use different wavelengths (918nm and 980nm) to core-pump a Yb:Al fiber to measure the PD. The inversion levels are kept at same values at both pumping wavelengths. The PD is assessed by temporal transmitted power decay at 620 nm as a probe beam, and transmission spectra change after the PD. The results reveal that under the same inversion level, 980 nm pumping can lead to more significant photodarkening effect than 918 nm counterpart. In addition, the 980 nm pumping wavelength induce stronger UV emission, which might suggest the UV emission is related to the creation of the PD. Our results indicates that using 918 nm pumping source would be helpful to reduce the PD.

9728-111, Session PTue

Stable and narrow-linewidth wavelength swept laser at 800nm based on acousto optic tunable filter Gahee Han, Nam-Su Park, Chang-Hyun Park, Chang-Seok Kim, Pusan National Univ. (Korea, Republic of) We proposed a stable and narrow-linewidth wavelength swept laser source at the 800 nm region using an acousto-optic tunable filter (AOTF) and a passive fiber ring resonators (FRRs). In swept-source optical coherence tomography (SS-OCT), factors of wavelength swept laser such as linewidth and wavelength stability are dependent on the image depth and image stability. It is consists by a semiconductor optical amplifier (SOA), a fiber isolator, a fiber coupler, an AOTF and two passive FFRs. Conventional sweeping has been performed by mechanical filter such as fabry-perot tunable filter (FFP-TF) and galvanometer. However, mechanical movement complicates the device design and thus induces the limited stability and tuning speed. Recently, it has been known that AOTF is capable of yielding stable and fast performance. It offers a wide tuning range, high tuning speed and stable operation against vibration and temperature due to non mechanical. The narrow linewidth is realized by a passive fiber ring resonators (FRRs), which consists of two FRRs. Owing to the vernier effect, each lasing modes can be significantly suppressed to obtain the narrower linewidth. As a result, the single longitudinal mode can be successfully demonstrated. The FFRs, which corresponds to a longitudinal mode space of each length, are implemented by simply connecting ports of 3-dB fiber

56

couplers. The novel wavelength swept laser source will offer high stable and narrowlinewidth, which especially benefits for image depth and image stability for optical coherence tomography (OCT) and high sensitivity for optical sensor

9728-112, Session PTue

A passively mode locked thulium doped fiber laser using bismuth telluride deposited multimode interference Minwan Jung, Korea Institute of Science and Technology (Korea, Republic of) and Univ of Seoul (Korea, Republic of); Junsu Lee, The Univ. of Seoul (Korea, Republic of); Wongeun Song, Advanced Photonics Research Institute (Korea, Republic of) and The Univ. of Seoul (Korea, Republic of); Ju Han Lee, The Univ. of Seoul (Korea, Republic of); Woojin Shin, Gwangju Institute of Science and Technology (Korea, Republic of) High peak power ~2 ?m pulse lasers are practically useful in numerous applications, such as eye-safe LIDAR, medicine, spectroscopy, remote sensing and mid-infrared (IR) generation. Especially, optical fiber lasers exhibit a range of advantages over their bulk optics-based counterparts in terms of beam quality, reliability, and environmental stability. The mode-locking technique is commonly used to obtain high peak power by generating short pulses in a laser cavity and the broad gain at ~2 ?m of Thulium doped fiber allows potentially ultra-short pulse operation in modelocked laser. The saturable absorbers such as semiconductor saturable absorber mirror (SESAM), polarization beam splitter (PBS), fiber loop mirror, carbon nanotube (CNT), graphene and topological insulator have been deployed passively mode-locked fiber lasers. The saturable absorber based on topological insulators has been attracting much attention due to its broad operation wavelength comparing to the other methods, and simplicity for forming the fiber based saturable absorption devices such as a sandwiching method, a D-shaped fiber, a tapered fiber. In this paper, we proposed all fiber saturable absorption devices that has spectral filtering property using a bismuth telluride and MMI interaction. By deploying the proposed MMI based saturable absorber, a wavelength fixed passively mode locked thulium doped fiber laser was demonstrated operating at a wavelength of 1958 nm. The optical bandwidth of ~4 nm is experimentally obtained at a repetition rate of 22.7MHz.

9728-113, Session PTue

Wavelength selective Tm doped all fiber laser using grating pair and null core fiber Wongeun Song, Advanced Photonics Research Institute (Korea, Republic of) and The Univ. of Seoul (Korea, Republic of); Minwan Jung, Advanced Photonics Research Institute (Korea, Republic of) and Univ. of Seoul (Korea, Republic of); Daeyoung Kim, Advanced Photonics Research Institute (Korea, Republic of); Ju Han Lee, The Univ. of Seoul (Korea, Republic of); Bong-Ahn Yu, Woojin Shin, Advanced Photonics Research Institute (Korea, Republic of) We firstly proposed all-fiber band pass filter (BPF) operating at 2 um wavelength using concatenation of long period fiber grating (LPFG), null core silica fiber (NCSF) and long period fiber grating (LPFG). The first and the second LPFG have same resonance dip. When the light has met the first LPFG, according to phase-matching condition, the fundamental core mode couples to the cladding mode and the Rest of light except the first

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications LPFG’s resonant wavelength continues to propagate through the core of the fiber and it experiences high transmission loss at NCSF section. Therefore, NCSF plays the role of core mode blocker in this structure. At the second grating, the cladding mode light is coupled to the core mode at the second LPFG that has same resonant wavelength of the first LPFG. After the light pass through the proposed LPEG-NCSF-LPFG structure, it shows band pass filtering characteristics at resonance wavelength of LPFG pair. The distance between the two LPFG centers including the NCSF segment was less than 70 mm and the total length of the device was less than 120 mm. The fabricated BPF has 4.2 dB insertion loss and less than 1 dB polarization dependence loss (PDL). The full width half maximum of transmission band is measured about 12.4 nm. The transmission of non-resonant signals were suppressed more than 6 dB. In order to evaluate the proposed device as a wavelength selective device, a wavelength selective Thulium doped fiber was demonstrated using the proposed device as a wavelength selector in the laser cavity. As the proposed device has a merit of all fiber device such as cost-effective, compactness and high power endurable, the proposed device could be used as an all fiber wavelength selective component in various applications at 2 um wavelength.

9728-114, Session PTue

Enhanced higher order mode delocalization through highly asymmetric rod-type VLMA fiber Zeinab Sanjabi Eznaveh, J. E. Antonio Lopez, Gisela LópezGalmiche, James Anderson, Axel Schülzgen, Rodrigo Amezcua Correa, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States) We propose and experimentally investigate a novel design of a microstructured single mode (SM), very large mode area (VLMA) ytterbiumdoped rod type fiber amplifier featuring an enhanced higher-order mode (HOM) delocalization and efficient preferential gain in active fibers. The proposed fiber design consists of six high-index germanium-doped silica rods integrated asymmetrically in the cladding of the fiber structure in order to remove the reflection symmetry and therefore, weakening the overlap of the LP11-like modes with the fiber core. This innovative fiber design with a core diameter of 66?m enables effective SM operation close to diffraction limited beam quality M2 of 1.3 in a broad spectral range of 850-1600nm with mode field area (MFA) of 2560um2 at 1064nm. The enhanced features of this fiber implies the improved threshold like onset of modal instabilities in high power fiber amplifiers. To prove the robust SM operation of the fiber under any launching condition, we translated the input beam along x from -30?m to +30?m attempting to excite any HOM and recorded a series of near field images at 1064nm wavelength. No HOM was observed which confirms the effective SM operation of the asymmetric rod fiber. To demonstrate highly effective HOM delocalization, the spatially and spectrally (S2) resolved mode imaging measurement was used to yield the mode images as a function of group delay. The peaks in the FT spectrum were corresponding to the cladding modes which particularly proves the scalability of the HOMs’ filtering capability of the proposed fiber design.

9728-115, Session PTue

All-bismuth ultrafast fiber systems Teppo Noronen, Oleg G. Okhotnikov, Tampere Univ. of Technology (Finland) No Abstract Available

Return to Contents

9728-116, Session PTue

Simple all-PM-fiber laser system seeded by an all-normal-dispersion oscillator modelocked with a nonlinear optical loop mirror Jan Szczepanek, Tomasz M. Kardas, Univ. of Warsaw (Poland); Michal Nejbauer, Univ. of Warsaw (Poland) and Institute of Physical Chemistry (Poland); Czes?aw Radzewicz, Institute of Experimental Physics, Faculty of Physics, Univ. of Warsaw (Poland); Yuriy Stepanenko, Univ. of Warsaw (Poland) and Institute of Physical Chemistry (Poland) In this paper we report an all-PM-fiber laser amplifier system seeded by an all-normal-dispersion oscillator mode-locked with a Nonlinear Optical Loop Mirror (NOLM). The presented all-normal-dispersion cavity works in a dissipative soliton regime and delivers highly-chirped, high energy pulses above 2.5 nJ with full width at half maximum below 220 fs. After the allPM-fiber amplifying stage spliced directly to the output of the oscillator we received pulses with the energy above 42 nJ and time duration below 200 fs. The electrical field of optical pulses from the system was reconstructed using the SPIDER technique. The influence of nonlinear processes on the pulse temporal envelope was investigated.

9728-117, Session PTue

High average power harmonic modelocking of a Raman fiber laser based on nonlinear polarization evolution Jun Liu, Chujun Zhao, Shenzhen Univ. (China); Yanxia Gao, Shenzhen University (China); Dianyuan Fan, Shenzhen Univ. (China) We experimentally demonstrate the operation of a stable harmonically mode-locked Raman fiber laser based on the nonlinear polarization rotation technique. A maximum average output power of up to 235 mW is achieved at the repetition rate of 466.2 MHz, corresponding to the 1695th order harmonic mode-locking operation. The temporal width of the mode-locked pulse train is 450 ps. The experimental results should shed some light on the design of wavelength versatile ultrashort lasers with high average output power.

9728-118, Session PTue

486nm blue laser operating at 500 kHz pulse repetition frequency Daniel Creeden, Jon Blanchard, Herman Pretorius, Julia Limongelli, Scott D. Setzler, BAE Systems (United States) Compact, high power blue light in the 470-490nm region is difficult to generate due to the lack of laser sources which are easily convertible (through parametric processes) to those wavelengths. By using a pulsed Tm-doped fiber laser as a pump source for a 2-stage second harmonic generation (SHG) scheme, we have generated ~2W of 486.5nm light at 500kHz pulse repetition frequency (PRF). To our knowledge, this is the highest PRF and output power achieved in the blue region based on a frequency converted, monolithic fiber laser. This pump laser is a pulsed Tm-doped fiber laser/amplifier which generates 12W of 1946nm power at 500kHz PRF with diffraction-limited output from a purely single-mode fiber. The output from this laser is converted to 973nm through second harmonic generation (SHG). The 973nm is then converted to 486.5nm via another SHG stage. This architecture operates with very low peak power, which can

+1 360 676 3290 · [email protected]

57

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications be challenging from a nonlinear conversion standpoint. However, the low peak power enables the use of a single-mode monolithic fiber amplifier without undergoing nonlinear effects in the fiber. This also eliminates the need for novel fiber designs, large-mode area fiber, or free-space coupling to rod-type amplifiers, improving reliability and robustness of the laser source. Higher power and conversion efficiency are possible through the addition of Tm-doped fiber amplification stages as well as optimization of the nonlinear conversion process and nonlinear materials. In this paper, we discuss the laser layout, results, and challenges with generating blue light using a low peak power approach.

9728-119, Session PTue

Generation of broadband mid-infrared supercontinuum radiation in cascaded soft-glass fibers Christian Kneis, Institut Franco-Allemand de Recherches de Saint-Louis (France) and Univ. Bordeaux 1 (France); Thierry Robin, Benoît Cadier, iXFiber SAS (France); Inka Manek-Hönninger, Univ. Bordeaux 1 (France); Marc Eichhorn, Christelle Kieleck, Institut Franco-Allemand de Recherches de Saint-Louis (France); Laurent Brilland, Selenoptics (France); Johann Troles, Celine Caillaud, Institut des Sciences Chimiques de Rennes, University of Rennes (France) The generation of mid-infrared (mid-IR) radiation, ranging from 2 - 5 µm, is getting much attention in the recent years thanks to many applications it can be used for, e.g. in free space optical communication systems, range finding and remote chemical sensing applications. It also plays an increasing role in medicine, for instance in optical tissue ablation or optical coherence tomography, owing to the high water absorption in that wavelength range. In this research study, a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber is pumped by a Q-switched mode-locked (QML) thulium (Tm3+)-doped double-clad fiber laser, emitting at 2 µm, to generate mid-IR supercontinuum (SC). Further spectral broadening is achieved by pumping a chalcogenide photonic crystal fiber (PCF) with the SC radiation from the ZBLAN fiber. Different ZBLAN fiber designs and chalcogenide materials are characterized and compared regarding their potential for broadband high average output power performance. So far, 24 W of 2 µm radiation in QML regime has been achieved with 5.1 W SC output power from the ZBLAN fiber. The broadest SC spectrum from the ZBLAN fiber went up to 4.1 µm. First proof of principal experiments with a germanium-arsenide-selenide (GeAsSe) PCF fiber showed wavelength broadening up to 4.4 µm with an output power level of 5 mW. The pump power has been 50 mW of SC radiation from the ZBLAN fiber with a spectrum from 3.5 µm to 3.9 µm. The coupling efficiency of the ZBLAN radiation into the GeAsSe fiber has been around 30%. Power scaling of the SC generation in the ZBLAN and the chalcogenide fiber will be shown and further spectral broadening.

9728-120, Session PTue

High power narrow bandwidth fiber amplifier with a FBG-based seed Jinping Hao, Hong Zhao, Dayong Zhang, Liming Zhang, Kun Zhang, North China Research Institute of Electrooptics (China) Narrow bandwidth fiber laser has drawn increasing attention for its use in unique application areas such as gravitational wave detection, range finding, lidar, and coherent beam combination. However, power scaling of such laser is mainly prohibited by stimulated Brilliouin scattering (SBS) - one type of nonlinearity effects. Previous solutions to SBS limitation either call for additional control or increase the complexity of the laser, which could affect

58

the laser’s stability. In this paper, an all-fiber kW-level narrow bandwidth amplifier with concise profile is demonstrated. The seed of the amplifier is an oscillator built on a pair of narrow bandwidth fiber Bragg gratings (FBGs). The FBGs help to assure a narrow bandwidth output of the amplifier as 0.078 nm. The amplifier achieves near diffraction limited output of 823 W, which is the known highest power output for a narrow bandwidth fiber amplifier seeded by a FBG-based oscillator. And the opto-optic efficiency reaches 84.5%, which is rather high for a fiber amplifier, especially for a narrow bandwidth one. In the amplifier configuration, a newly designed cladding stripper with segment-based structure is brought in, realizing high efficiency and high power cladding light leakage. Besides, the mechanism of laser operation in a narrow bandwidth fiber amplifier is studied and simulated. Influences of seed and fiber parameters on SBS threshold in such amplifier are discussed as well, which provides guides in further power scaling of narrow bandwidth fiber lasers.

9728-121, Session PTue

Millijoule class, all-fibered front end nanosecond pulse, single frequency, with spatially coherent top-hat beam output used as seeder for high power laser: current status and future perspectives of industrial version Jean-François Gleyze, Arnaud Perrin, Pierre Gouriou, Florent Scol, Commissariat à l’Énergie Atomique (France); Constance Valentin, Géraud Bouwmans, Lab. de Physique des Lasers, Atomes et Molécules (France); Emmanuel Hugonnot, Commissariat à l’Énergie Atomique (France) In large scale laser facility dedicated to laser-matter interaction including inertial confinement fusion, such as LMJ or NIF, high-energy main amplifier is injected by a laser source in which the beam parameters must be controlled. For many years, the CEA has developed nano-joule pulses all-fiber front end sources, based on the telecommunications fiber optics technologies. Thanks to these technologies, we have been able to precisely control temporal shaping and phase-modulated pulse. Nowadays, fiber lasers are able to deliver very high power beams and high energy pulses for industrial needs (laser marking, welding,…). This new fiber laser technology has a great potential to improve stability and versatility of high-energy system front-end. Therefore, we have currently developed new nanosecond pulses fibered amplifiers able to increase output pulse energy up to the mJ level. These amplifiers are based on flexible fibers and not on rod type. This allows us to achieve a compact source. To be compatible with main amplifier section injection, the Gaussian intensity profile of fibered system must be transformed into ‘top-hat’ profile. To reach this goal, we have recently developed an elegant and efficient solution based on a single-mode fiber which directly delivers a spatially coherent ‘top-hat’ beam. In this conference, we will present last results of mJ-class top-hat all-fiber laser system, the results and the industrial prototype which can be used as a front-end of high-power lasers or as a seeder for other types of lasers. We will discuss the opportunity of such a system in LMJ architecture.

9728-122, Session PTue

2.9 GHz 780w narrow linewidth fiber laser Hong Zhao, Nianjiang Chen, North China Research Institute of Electro-optics (China) Narrow linewidth fiber lasers are wide applied in coherent detection, gravitational wave detection, coherent beam combing and wavelength

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications beam combining.But in HPNL fiber laser, the main limitation factor of power increasing is SBS. Through sinusoidal phase modulating single frequency laser, we can increase longitudinal mode number. And then SBS can be suppressed. So, the keystone of sinusoidal phase modulation is analyzed.

can be no better than that of an individual element. This is known as side-by-side beam combining. Polarization beam combining is often used to combine two arrays of orthogonal polarization. This can increase the brightness a factor of 2 at best.

The keystone of sinusoidal phase modulation is LiNbO3 crystal composing phase modulator, its refractive index changing under outward electric field influence and then input light wave modulated. The light that is inputted into phase modulator is called carrier frequency.The light spectrum broadening is the full width at half maximum (FWHM) of waveform envelope, which is composed with these sideband frequency spectrums. The frequency distribution of sinusoidal phase modulating single frequency laser is simulated. The electrical frequency is 150MHz. Phase modulating coefficient is.

There are two approaches, wavelength beam combining (WBC) and coherent beam combining (CBC), to scaling the brightness by large amounts, in principle by as much as the number of elements. In WBC, the array elements operate at different wavelengths and a dispersive optical system is used to overlap the different wavelengths spatially. Typical dispersive optical systems use gratings, prisms, or wavelength-selective reflectors. This is equivalent to what is done in wavelength division multiplexing for optical communications. The differences here are that the goal is higher power, and, therefore, the efficiency is more important. In CBC, the beams are interferometrically combined, or phased. If the beams are phased properly, then constructive interference occurs and the power can be combined into a single beam.

The laser is composed of seed source adding three stage amplifier. Wherein, single frequency laser diode is employed as the seed source with 50mW, 1064.34nm and less than 1MHz. The phase modulator is employed to broaden spectrum. Its electro optical bandwidth, half wave voltage, maximum modulating voltage peak to peak value and maximum endured optical power are 150MHz, 2.5V, 20V and 20dBm, respectively. High frequency signal generator is employed as sinusoidal electrical signals to trigger source. Its output frequency range and maximum output power are 65kHz to 8GHz and 16dBm, respectively. The radio frequency driver (RF driver) is used to amplify electrical signals. Its cut-off frequency, saturated output power and maximum gain are 20GHz, 26dBm and 30dB, respectively. In experiment, the signal generator output frequency is 150MHz. The phase modulating coefficient are , and , respectively. In the first and second amplifier stage, Yb3+ doped double cladding fiber with core/cladding diameter of 10/130?m and length of 3m is employed as gain fiber (10/130 YDF). Its absorption coefficient is 3.9dB/m at 975nm. In the third amplifier stage, Yb3+ doped double cladding fiber with core/ cladding diameter of 25/400?m and length of 12m is employed as gain fiber (25/400 YDF). Its absorption coefficient is 1.6dB/m at 976nm. To prevent feedback, an optical isolator (ISO) is connected between each stage. The second and third amplifier stage is connected by mode field adaptor (MFA). In order to eliminate the cladding light, the cladding light stripper is connected between the third and output end. In order to prevent the backward scattering light bashing the front stage device, a tap coupler is connected between the second and three amplifier stage. Its splitting ratio is 5/95. Its function is to monitor reverse SBS power (SBS monitor). When the reverse power growing nonlinearly, showing that SBS has reached threshold. In this moment, the amplifier stage power supply should be shut off quickly to prevent the front stage device being bashed.

9728-41, Session 9

High-power, high-brightness laser beam combining (Invited Paper) John D. Hybl, Darren A. Rand, MIT Lincoln Lab. (United States) There is continuing interest in increasing the power and improving the beam quality of laser sources for a variety of applications including materials processing, pumping, power transmission, and illumination. One approach is to continue to develop improved lasers with higher power and good beam quality. Another approach, particularly relevant to semiconductor and fiber lasers, is to beam combine large arrays of lasers. Beam combining has become increasing viable over the past decade as the community has developed a better understanding of the requirements imposed by beam combining, and various implementations have been successfully demonstrated in the laboratory. These implementations are beginning to see commercial application.

This tutorial will cover the fundamentals of laser beam combining, including requirements on the array elements, basic scaling laws, and implementations. Examples from the literature will be used to show the progress being made.

9728-42, Session 9

Femtosecond fiber-CPA system employing coherent combination of a multicore fiber Arno Klenke, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz Institute Jena (Germany); Michal Wojdyr, Michael Müller, Friedrich-Schiller-Univ. Jena (Germany); Marco Kienel, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz-Institute Jena (Germany); Jens Limpert, Andreas Tünnermann, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz-Institute Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany) Coherent combination of multiple amplifiers has become an established technology to overcome limitations of the average power, peak power and pulse energy of fiber-CPA systems. However, so far, these systems were built by duplicating standard single amplifier systems and adding the necessary components to realize the combination process. This limits the realistically achievable number of channels due to constraints of the footprint and component count. Therefore, the integration of multiple signal channels in a multicore fiber is of major interest. In this contribution, we present coherent combination using an ytterbiumdoped multicore fiber as the main amplifier in a femtosecond fiber-CPA system. The fiber possesses four signal cores with a mode-field diameter of 36 µm each and a shared pump cladding. The incident beam from the frontend is split into four parallel beams with a segmented-mirror splitter (SMS). This splitter consists of a high reflective mirror and a second mirror with zones of different reflectivities. The beams are coupled into the signal cores of the multicore fiber and after amplification, they are recombined into a single beam again using a second SMS. A LOCSET stabilization system is employed to optimize the path lengths for constructive interference at the output. After compression, the system can emit up to 120 µJ pulses with a duration of 250 fs and a drastically improved pulse quality compared to a single core fiber. Due to the compact setup of this amplifier, laser systems with a large number of coherently combined channels will be realizable in the future.

Key metrics for high-power arrays include the output power, the brightness, and the spectral width. To achieve high brightness, both high power and good beam quality are required. High-power diode arrays currently are composed of large numbers of emitters tiled side-by-side with the emitters being mutually incoherent with respect to each other. As the number of array elements increases, the beam quality decreases, and the brightness

Return to Contents

+1 360 676 3290 · [email protected]

59

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications

9728-43, Session 9

Self-compression to 24 MW peak power in a fused silica solid-core fiber using a highrepetition rate thulium-based fiber laser system Martin Gebhardt, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz Institute Jena (Germany); Christian Gaida, Fabian Stutzki, Friedrich-Schiller-Univ. Jena (Germany); Steffen Hädrich, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz Institute Jena (Germany); Cesar Jauregui, Friedrich-Schiller-Univ. Jena (Germany); Jens Limpert, Andreas Tünnermann, Friedrich-Schiller-Univ. Jena (Germany) and Helmholtz Institute Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany) Complementing ultrafast thulium-based fiber-laser systems with subsequent nonlinear pulse compression can enable unique laser parameters at around 2 µm operation wavelength. Significant pulse shortening and peak power enhancement have been accomplished using a fused silica solid-core fiber. In this fiber a pulse peak power of 24 MW was achieved without catastrophic damage due to self-focusing. As compared to operation in the well-explored 1 µm wavelength regime increasing the emission wavelength to 2 µm is of twofold advantage for nonlinear compression in fused-silica solid-core fibers. This is because on the one hand the self-focusing limit scales quadratically with the wavelength. On the other hand the dispersion properties of fused silica allow for self-compression of ultrashort pulses beyond 1.3 µm wavelength, which leads to strong spectral broadening from very compact setups without the need of external compression. Using this technique we have generated 1 µJ-pulses with 24 fs FWHM pulse duration (10mJ pulse energy in ultrashort pulses from a fiber CPA system with negligible nonlinear distortions.

9728-45, Session 9

Electro-optically controlled divided-pulse amplification Michael Mueller, Marco Kienel, Michal Wojdyr, Arno Klenke, Jens Limpert, Andreas Tünnermann, Friedrich-SchillerUniv. Jena (Germany) Today, high-power femtosecond laser systems enable demanding industrial and scientific applications. The occurrence of nonlinear effects up to optically induced damage limit performance scaling, even after applying elaborate methods such as chirped-pulse amplification. Coherent beam combination and divided-pulse amplification are promising techniques to exceed the current limitations by temporally increasing the beam area and the pulse duration, respectively. Actively stabilized implementations achieved the highest combining efficiencies even for strong amplifier saturation and large nonlinear phase accumulation. However, the system complexity and the alignment sensitivity grow fast – asking for higher system integration. In this contribution, we present a spatiotemporal combining setup in a proof-of-principle experiment with an entirely fiber-coupled front-end. Unlike in previous experiments, where the temporal pulse division was achieved using free-space optical delay lines, the pulses are taken directly from the pulse train of the oscillator. Also the spatial division is totally fiber coupled. Thereby, the free-space paths and the alignment requirement are cut in half. However, the combination inevitably remains in free-space considering application in high-power lasers. For the combination of 4 pulses, a combining efficiency larger than 95% is demonstrated. The efficiency is largely independent of the combined pulse energy and the temporal pulse contrast is better than 20 dB. Potentially, this approach allows for self-optimization of the combination due to the many degrees of freedom accessible with the EOMs.

9728-44, Session 9

Cascaded coherent pulse stacking from fiber chirped-pulse amplifiers Tong Zhou, John M. Ruppe, Cheng Zhu, John A. Nees, Univ. of Michigan (United States); Russell B. Wilcox, Lawrence Berkeley National Lab. (United States); Almantas Galvanauskas, Univ. of Michigan (United States) We are developing a new technique of cascaded coherent pulse stacking (CPS) for enhancing ultrafast pulse energies from fiber chirped-pulse amplification (CPA) systems by a factor of up to 100-1000 times. It is based on coherent temporal combining of a sequence of amplified chirped equal-amplitude input pulses into a single chirped output pulse using GiresTournois interferometers (GTI). Cascaded CPS is accomplished with a burst of N equal-amplitude input pulses by storing all the energies of the first N-1 input pulses in the cavities through destructive interference at the partial reflector of the final GTI, followed by sequential extraction of the energy from each cavity through constructive interference of the N-th pulse with the intra-cavity pulses at the partial reflectors. The GTI roundtrip length can be folded using Herriott cells, which are essentially compactly folded optical delay lines and can greatly reduce the footprint of the GTIs.

60

In a proof-of-principle experiment of cascaded coherent pulse stacking, an amplified chirped-pulse burst mainly consisting of four equal amplitude pulses is coherently stacked into a single output pulse using two cascaded GTIs with a normalized pulse energy enhancement of 3.64 times. Input pulse burst is modulated using electro-optic modulators directly after a 122MHz mode-locked oscillator and a stretcher, and amplified into the microjoulemillijoule range prior to stacking using an amplification chain with a final 55?m chirally-coupled-core (CCC) fiber amplifier.

9728-46, Session 10

Single frequency 1560nm Er:Yb fiber amplifier with 207W output power and 50.5% slope efficiency Daniel Creeden, Herman Pretorius, Julia Limongelli, Scott D. Setzler, BAE Systems (United States) High power fiber lasers/amplifiers in the 1550nm spectral region have not scaled as rapidly as Yb-, Tm-, or Ho-doped fibers. This is primarily due to the low gain of the erbium ion. To overcome the low pump absorption, Yb is typically added as a sensitizer. Although this helps the pump absorption, it also creates a problem with parasitic lasing of the Yb ions under strong pumping conditions, which generally limits output power. Other pump schemes have shown high efficiency through resonant pumping without the need for Yb as a sensitizer. Although this can enable higher power scaling due to a decrease in the thermal loading, resonant pumping methods require long fiber lengths due to pump bleaching, which limits the power scaling which can be achieved for single frequency output. By using an

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications Er:Yb fiber and pumping in the minima of the Yb pump absorption at 940nm, we have been able to simultaneously generate high power, single frequency output at 1560nm while suppressing the 1-micron ASE and enabling higher efficiency compared to pumping at the absorption peak at 976nm. We have demonstrated single frequency amplification (540Hz linewidth) to 207W average output power with 49.3% optical efficiency (50.5% slope efficiency) in an LMA Er:Yb fiber. We believe this is the highest reported efficiency from a high power 9XXnm pumped Er:Yb-doped fiber amplifier. This is significantly more efficient that the best-reported efficiency for high power Er:Yb doped fibers, which, to-date, has been limited to ~41% slope efficiency.

9728-47, Session 10

Polarization maintaining, very-large-mode area, Er fiber amplifier for high energy pulses at 1572.3 nm Jeffrey W. Nicholson, Anthony M. DeSantolo, Man F. Yan, Patrick W. Wisk, Brian J. Mangan, Gabe S. Puc, OFS Fitel LLC (United States); Anthony W. Yu, Mark A. Stephen, NASA Goddard Space Flight Ctr. (United States) Very-large-mode area (VLMA) Er-doped fiber amplifiers , core pumped by high-power 1480 nm, Raman fiber lasers, generate diffraction limited, high energy pulses at 1.5 micron wavelengths, and have applications in femtosecond fiber chirp-pulse amplifiers [ ] and high-energy soliton generation, for example. They have been demonstrated with core diameters greater than 50 microns and effective areas greater than 1100 square microns. In spite of the success of VLMA Er amplifiers, there have been few results on making polarization maintaining large-mode area Er-doped fibers. A 26 micron mode-field diameter (~ 530 square micron Aeff) polarization maintaining, Er-Yb doped photonic crystal fiber laser was previously demonstrated. In this work, we demonstrate for the first time, a polarization maintaining, Er-doped VLMA amplifier with greater than 1000 square micron effective area. We then use this amplifier to demonstrate high energy, one microsecond pulse amplification at 1572.3 nm. The CO2 absorption line centered at 1572.3 nm has been chosen due to confluence of several spectroscopic properties. It is relatively insensitive to temperature changes compared to other lines in the absorption band, free of absorption features from other atmospheric constituents, and has a convenient peak absorption amplitude that allows measurement of the full atmospheric column that optimizes SNR (i.e - it does not saturate, but is a large enough feature that it is easy to distinguish from background variations.). Single frequency, 1572.3 nm, 1 microsecond pulses at 7.2 kHz repetition frequency were amplified to 400 W peak power with a pulse energy of 368 microJoule. Polarization extinction ratio of the signal was better than 20 dB, and M2 = 1.1.

1. Introduction Efficient power scaling of eye-safe Yb-free Er-doped silica fiber lasers based on 4I13/2 ? 4I15/2 transitions of Er3+ ions is hindered by low Erbium concentration due to low solubility of Er and a trend of Er ions to clustering in silica glass fibers. A typical core pump absorption of Erbium doped LMA silica fiber at 1530 nm is ~ 60 dB/m which is ~20 times lower than that of Yb doped silica LMA fibers (1200 dB/m). Due to the low core absorption a much smaller clad-to-core ratio is required to retain reasonable clad absorption, which inevitably limits the total diode pump power that can be coupled in the cladding. Recent development of Er-doped silicate glass indicates that the novel silicate material is able to accept much higher Er concentration before clustering, which results in a 300-500 dB/m core pump absorption. Recently, 75% laser efficiency was demonstrated with resonant pumping from the 100 µm clad diameter silicate glass fiber [1]. Presented here are the results of resonantly (in-band) diode-pumped fiber laser power scaling with a new LMA triple-clad silicate glass fiber. Some of the fiber parameters are presented in Table 1. 13 individual InGaAsP/InP based, volume Bragg grating (VBG)-narrowed (?? = 2 nm FWHM), 1530-nm fiber coupled laser diode modules were combined into a single fiber output using a 13x1 ITF pump combiner. The combiner output is a 250 µm, 0.46 NA fiber matching the pump cladding of the Er-doped silicate fiber. Figure 1 indicates a simplified experimental setup. A pair of Semrock filters performs as a sharp edge dichroic wavelength separator with ~40 dB extinction ratio between the pump and laser wavelengths. A VBG or a broadband HR mirror are used to provide >99% laser feedback. VBG with the HR bandwidth of 1.5 nm at 1570 nm provides a laser wavelength selection, as needed. Broadband HR mirror provides a non-selective laser feedback. The pump end of the fiber is a straight cleave with 5.2% Fresnel reflection. The output signal is reflected by the second pump filter and analyzed. Figure 2 shows the laser performance of the fiber. A fiber lengths of 10, 7, and 3 meters were used for Figure 2 shows the laser performance of the fiber. A fiber lengths of 10, 7, and 3 meters were used for optimization of optical efficiency. Over 100 W of CW output is achieved with the fiber of 10 meter length. 55% efficiency was observed with the fiber length of ~7 meters. Laser output was characterized spectrally and spatially. We found the fiber output to be nearly single-mode. We will present the fiber laser performance with two types of mirrors, VBG and non-selective broad band mirror. We also measured a pretty high propagation loss of 0.3 dB/m, which happens to be a major contributor to optical efficiency being much lower than the quantum defect limited. Due to relatively high heat deposition level fiber laser operation required water cooling. Due to observable fiber microdefects at this early development stage fiber damage occurs at the pumped fiber tips during high power operation. We believe that much better efficiency and operation stability can be achieved with improved material quality. In conclusion, we have demonstrated a scalability potential of a newly developed triple-clad silicate glass fiber with highly Er–doped core. With resonant diode pumping we achieved a laser output power of over 100 W at 1615.3 nm which is believed to be the highest output power achieved from fiber laser based on a silicate glass fiber. References:

9728-48, Session 10

Power scaling of Er-doped LMA triple-clad fiber laser based on silicate glass Jun Zhang, Youming Chen, Radha Pattnaik, Mark Dubinskii, U.S. Army Research Lab. (United States); Shibin Jiang, AdValue Photonics, Inc. (United States) A triple-clad silicate glass fiber with highly Er–doped core has been studied in a resonantly (in-band) pumped fiber laser configuration. Over 100 W laser output power at 1615.3 nm has been achieved with laser diode pumping at ~1530 nm and an optimized fiber length. To the best of our knowledge, it is the highest output power ever achieved from the fiber laser based on a silicate glass fiber. An efficiency of 55% (laser output versus absorbed pump power) was achieved in this first major power scaling experiment.

Return to Contents

1. Qiang, ZX; Geng, JH; Luo, T; Zhang, J; Jiang, SB, “High-efficiency ytterbium-free erbium-doped all-glass double cladding silicate glass fiber for resonantly-pumped fiber lasers”, Appl. Opt. 53 (4), pp. 643-647 (2014).

9728-49, Session 11

Eye-safe ns pulses from a high-aspectratio-core fiber amplifier Fabio Di Teodoro, Raytheon Co. (United States); Friedrich P. Strohkendl, Raytheon Space and Airborne Systems (United States) High-peak-power, eye-safe ns-pulse fiber sources are well suited to remote sensing owing to good atmospheric transmission, spectral compatibility

+1 360 676 3290 · [email protected]

61

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications with mature photo-detectors, reliance on telecom component/materials, and usability in environments where glint can reach bystanders. To scale peak power with low nonlinear effects, fibers of larger cores are required, in which it is generally difficult to have at once good beam quality and support for tight coiling. To address this issue, we use the semi-guiding high-aspect-ratio-core (SHARC) fiber concept. SHARC fibers feature elongated rectangular cores. In the short dimension, the fiber core behave as those in single-mode or large-mode area fibers. Tight coiling is thus possible. In the orthogonal, elongated dimension, all modes are actually leaky, the fundamental transverse mode being favored by differential loss design. Confined rare-earth-doping further helps select the fundamental mode via the greater spatial overlap with the transverse doping profile. We amplified 1ns, 30kHz-rep.-rate, 1560nm pulses in an Er-doped SHARC fiber having mode-field area of approximately 2000 sq. microns. The fiber (~5m long) was coiled at ~15cm diameter and in-band core-pumped by a 1470nm Raman fiber laser. In-band core-pumping provides low quantum defect heating and high pump absorption per unit length, which permit the use of short, lower-nonlinearity, fibers while keeping waste heat removal manageable. From the SHARC fiber, we obtained peak power ~ 100 kW with good spectral and spatial quality. Much higher peak power is anticipated in other SHARC fibers being developed characterized by mode areas > 20,000 sq. microns and same coiling diameters.

9728-50, Session 11

Temperature measurements in an ytterbium fiber amplifier up to the mode instability threshold Franz Beier, Friedrich-Schiller-Univ. Jena (Germany); Matthias Heinzig, Till Walbaum, Nicoletta Haarlammert, Thomas Schreiber, Ramona Eberhardt, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany); Andreas Tünnermann, Friedrich-Schiller-Univ. Jena (Germany) and Fraunhofer-IOF (Germany) The output power scalability of Ytterbium doped high-power fiber lasers is limited by several effects, e.g. mode instabilities and the thermal destruction of the rare earth doped fiber as well as of passive components. Since mode instabilities are a thermo-optical effect, the longitudinal thermal load and the resulting temperature distribution are of high interest to develop and substantiate the understanding of such limitations. We report on the measurement of the longitudinal temperature distribution in an amplifier fiber during high power operation. The measurement signal of an optical frequency domain reflectometer is coupled to an ytterbium doped amplifier fiber via a wave division multiplexer. The mode instability threshold of the fiber under investigation was determined to be 870?W. In a first experiment, the longitudinal temperature distribution was examined for different pump powers with a sub mm resolution. The results show even small temperature variations induced by slight changes of the environmental conditions along the fiber. With respect to the ytterbium ion interaction between 910 and 1150?nm, an OFDR laser source in the 1300?nm region was used. A clad light stripper prevents the passive optical components from the destruction by residual pump light. The longitudinal temperature distribution was determined for different pump powers up to a signal output power of 300?W. The mean temperature is increasing by an increased pump power and a maximum temperature increase of 10?K was measured. The qualitative progression of the longitudinal temperature distribution corresponds to the results of a rate equation simulation.

9728-51, Session 11

Efficient ytterbium-doped phosphosilicate double-clad leakage-channel-fiber laser at 1008-1020 nm Guancheng Gu, Clemson Univ. (United States); Zhengyong Liu, The Hong Kong Polytechnic Univ. (Hong Kong, China); Fanting Kong, Clemson Univ. (United States); Hwa-Yaw Tam, The Hong Kong Polytechnic Univ. (Hong Kong, China); Ramesh K. Shori, SPAWAR Systems Ctr. (United States); Liang Dong, Clemson Univ. (United States) Thermal management is critical for kw-level power lasers, where mode instability driven by quantum defect heating is a major challenge. Tandem pumping using 1018nm fiber lasers are used to enable both high brightness and low quantum defect. It is, however, difficult to realize efficient 1018nm YDFL. The best demonstration to date is limited by the use of both conventional aluminosilicate host and smaller core diameters. In these cases, higher inversion is required due to the aluminosilicate host and higher pump brightness is required due to the smaller core, which results in high signal brightness for the same output power. These factors lead to large pump power to exit fiber, resulting in poor efficiency. Phosphosilicate host, on the other hand, requires much lower inversions to reach the gain threshold at 1018nm. The combination of phosphosilicate host and large-core leakage channel fibers (LCF) is a perfect candidate for efficient 1018nm fiber laser. We report a highly efficient Yb-doped phosphosilicate LCF laser with a quantum defect of 4.1% using a ~50µm-core diameter and ~420µm cladding diameter. The slope efficiency with respect to the launched pump power at 1018nm is 70%. The ASE suppression is >60dB. The large cladding of 420µm demonstrates a combination of high efficiency, ~4% quantum defect and high-power low-brightness diode pumping. We have also studied the limits of operating ytterbium fiber lasers at shorter wavelengths and found the efficiency to fall off at shorter wavelengths due to the much higher inversions required.

9728-52, Session 11

Extremely low NA Yb doped preforms (0.03) fabricated by MCVD Vincent Petit, Richard P. Tumminelli, Coherent, Inc., Salem (United States); John D. Minelly, Victor Khitrov, Coherent, Inc. (United States) We report the fabrication of extremely low NA preforms (2m fiber delivery cable. Customer reconfigurable features such as controllable repetition rate, fine pulse duration control, burst mode operation and adjustable pulse energy permit the customer to tailor the laser to their application.

9728-71, Session 15

Mechanical reliability of double clad fibers in typical deployment conditions Michael Walornyj, Jaroslaw Abramczyk, Kanishka Tankala, Nils Jacobson, Nufern (United States) Large mode area (LMA) double clad fibers (DCF) are widely used in high power laser applications. Optical reliability of DCFs has been studied and a predictive model for determining the fiber lifetime has been reported. While tensile strengths and n-values have been reported for DC fibers, mechanical reliability of fibers used in high power laser applications has yet to be studied. In these applications, large diameter LMA fibers are often tightly coiled to suppress higher order modes to achieve SM operation as well as to minimize form factor. The mechanical stresses resulting from bending large diameter fibers can significantly exceed those seen in the telecom industry. The mechanical reliability of telecom fibers has been thoroughly studied and models for predicting fiber lifetime for typical stresses experienced in deployment conditions are available. An analysis of the factors affecting the lifetime of DCF fibers in typical deployment conditions using such models has not been conducted. This paper, for the first time, will provide a comprehensive analysis all the factors impacting lifetime of LMA fibers. Furthermore, it highlights the choices manufacturers and users of DCF can make to enhance the longevity of the fibers. Nufern’s LMA-YDF-20/400 used in kW class fiber lasers is used as a case study to illustrate the parameters that impact mechanical service lifetime of the fiber.

Return to Contents

9728-72, Session 15

Novel all-polarization-maintaining femtosecond Yb-fiber laser for in-vivo nonlinear microscopy in zebrafish larvae Aart Verhoef, Medizinische Univ. Wien (Austria) and Technische Universtität Wien (Austria); Lingxiao Zhu, Univ. Wien (Austria) and Technische Univ. Wien (Austria); Marco Andreana, Medizinische Univ. Wien (Austria); Martin Distel, St. Anna Kinderkrebsforschung e.V. (Austria); Stine Møller Israelsen, Karsten Rottwitt, Technical Univ. of Denmark (Denmark); Wolfgang Kautek, Univ. Wien (Austria); Andrius Baltuska, Technische Univ. Wien (Austria); Alma del Carmen Fernandez Gonzalez, Medizinische Univ. Wien (Austria) and Technische Univ. Wien (Austria); Wolfgang Drexler, Angelika Unterhuber, Medizinische Univ. Wien (Austria) We developed a semiconductor saturable absorber mirror modelocked allPM femtosecond fiber laser where for the first time a PM higher-order-mode fiber was used for intracavity dispersion compensation. The ring cavity of the oscillator has a repetition rate of 12 MHz, the total intracavity cavity dispersion is close to zero. The oscillator delivers 0.45 nJ pulses that can be externally recompressed down to 97 fs, which to the best of our knowledge are the shortest pulses generated from an all-PM Yb-fiber oscillator. The observed 1 Hz linewidth, absence of any sidebands, and 80 dB signal/ background ratio of the output pulse train measured with an RF spectrum analyzer with 1 Hz resolution bandwidth illustrate the excellent stability of the oscillator. To allow for stronger signals and faster data collection for nonlinear microscopy, we amplify the pulses in a PM single-mode Yb-fiber amplifier to ~20 nJ after stretching them with 100 m of PM980. Using a pair of grisms we recompress the pulses to ~150 fs duration. With this source we have performed in-vivo nonlinear microscopy in zebrafish larvae, where we have simultaneously measured backscattered second harmonic and back-propagating fluorescence from two-photon excited red-fluorescent protein. To avoid optical damage to the larvae, the incident energy was limited to 5 nJ. Strong second harmonic signal can be observed from the collagen fibers in the tail finn, as well as from the muscles in a zebrafish tail. Fluorescence from macrofages labeled with mCherry, that can be used to identify cancer, is also observed.

9728-73, Session 15

Efficient pump combiner’s for fiber lasers and amplifiers Lalitkumar Bansal, Andrea Rosales-Garcia, OFS Fitel LLC (United States); V. R. Supradeepa, Indian Institute of Science (India); Thierry F. Taunay, Clifford Headley III, OFS Fitel LLC (United States) The power threshold for nonlinear effects in fiber lasers and amplifiers is inversely proportional to the fiber length. The required gain fiber length is in turn proportional to the cladding area of the gain fiber. In order to minimize nonlinearities, the smallest possible cladding diameter is desirable. On the other hand the amount of pump power that can be coupled into the gain fiber is proportional to its cladding area, and a large cladding is preferable. In an all fiber source configuration, pump light can be injected into the gain fiber by using a tapered fiber bundle [1]. This consists of multiple pump fibers that are closely packed together, tapered down and spliced to an output fiber. The output fiber is typically the same diameter as the gain fiber. As the bundle is tapered, the NA of the light that can propagate through it increases with the taper ratio. For low loss, the brightness condition, shown in Eq. 1 should be satisfied.

+1 360 676 3290 · [email protected]

67

Conference 9728: Fiber Lasers XIII: Technology, Systems, and Applications D_o^2 ?NA?_o^2 ≥ ?nD?_in^2 ?NA?_in^2 (1)

beam profile with a specific angular divergence.

Where Do/Din is the diameter of the output/input fiber, NAo/NAin is the numerical aperture of the output/input fiber, and n is the number of fibers in the bundle. The pump combiner design thus depends on the diameter and the NA of the diode pigtail fiber from a given diode manufacturer. Combiners based on a single bundle with up to 19 pump arms are typically available with pump transmission of 95%. When a larger number of pump ports is required, a so-called tree architecture shown in Fig. 1 offers a superior approach. It consists of a number of pump combiners which are spliced to the pump arms of a 2nd stage pump-signal combiner. This architecture has the additional advantage of simplifying the design for PM performance.

Here, a novel specialty fiber, made to satisfy the standard beam delivery (BD) cable requirements and designed to tailor mode up-conversion in a low maintenance and cost-effective single fiber device is reported.

A typical, industry-standard diode [2][3] uses 105/125 ?m (core/cladding) diameter pigtail fiber with light coupled into 0.15 NA. Based on Eq. (1) and using such diodes, typical commercially available 7x1 pump combiners designed to couple into 220/240 ?m diameter output fiber with 0.22 NA achieve pump transmission efficiency of about 90%.

Numerical and experimental results will be detailed for 50, 100 and 200 um core diameter fibers delivering flat-top beam profiles with BPP values around 2, 4 and 8 mm x mrad respectively. Moreover, results of high power testing of the specialty fiber beam delivery cable at 2 kW laser power will be presented.

To improve overall combiner performance, we have demonstrated a 1st stage pump combiner in which 7 diodes are combined into a 200/220 um 0.22 NA output fiber, with an average transmission of 99%, as seen in Fig. 2a. This improvement in pump combiner performance leads to a significantly improved high power tree pump combiner system. Figure 2b shows the transmission through the tree architecture using four such 7x1 multimode combiners. We have tested the optimized combiner system up to 1.3kW with 95% pump transmission efficiency and a thermal slope efficiency of 0.02 C/W, when heat sunk to a cooling plate at 25?C, the hottest spot was on the splice point which is 10 mm away from the fiber coating which is most prone to thermal damage. The (6+1)x1 PM single mode combiner has a 15/330 ?m output fiber with a signal loss of 0.2dB and a PER of 20dB. The overall pump transmission through the tree architecture is increase by 6% compared to trees based on commercially available combiners, offering a significant improvement in both efficiency and management of waste heat. The key characteristic of the combiner system is summarized in Table 1. An additional advantage of the improved pump combiner is that the output pigtail fiber now has 330 ?m cladding diameter as opposed to 400um, offering a significant improvement in pump brightness. This will translate into an approximately 50% increase in nonlinear thresholds for gain fibers with the same fiber core properties, due to the reduction in fiber length. With this device improved system efficiency, fewer diodes are needed, offering cost savings, and there is less burden on thermal management. In summary, we demonstrate a (42+1)x1 PM cascaded combiner system, with a 330um output cladding diameter, that has a 6% improvement in pump transmission compared to a standard 400 ?m combiner system. In addition, with this smaller cladding, and a correspondingly shorter fiber length the threshold for nonlinearities will increase. The combiner system has a high pump efficiency of 95%, driven by high efficiency 99% pump combiners. The pump and signal combiner has passed a high power handling test of 1.3 kW with thermal slope of 0.02 C/W, limited by available diode power.

Using numerical simulations based on spatial mode overlap calculations between the SM launch and the BD fiber, the design is optimized in order to achieve the required beam profile and beam divergence. According to the modeling predictions, a specialty fiber with 100 um core and 360 um cladding was fabricated and characterized with less than 2 dB/km attenuation in the 1 um wavelength range. Flat-top beam profile with a 3.8 BPP was demonstrated out of this fiber when coupling light from a SM 20 um core, 0.06 NA and 400 um cladding fiber laser.

9728-75, Session 15

Compact frequency-quadrupled pulsed 1030nm fiber laser Chris McIntosh, Lew Goldberg, Brian J. Cole, Alan D. Hays, U.S. Army RDECOM CERDEC NVESD (United States) A compact 1030nm fiber laser for ultraviolet generation at 257.5nm is presented. The laser employs a 35cm long polarization-maintaining 20um core (0.07 NA), 130um clad (0.45 NA) ytterbium fiber. In order to ensure lasing in the fundamental mode, the fiber was coiled into a 30mm diameter. One end of the fiber was flat-cleaved to serve as the output coupler, while the other end of the fiber was angle-cleaved. The light from a 975nm grating stabilized pump (0.1 NA, 105um clad diameter) was injected at a 15° launch angle using a 1:1 relay lens into the flat-cleave end of the fiber. A reflective long-pass filter was placed at the other fiber end to recycle the pump and a Cr:YAG saturable absorber (19% unsaturated transmission) was placed at the waist of a second 1:1 relay lens for passive Q-switching. A volume Bragg grating (VBG) was employed as the mirror. The fundamental 1030nm output was 2.0W average (in a 125uJ pulse train) for 10W launched pump power. A 15mm length of lithium triborate (LBO) was chosen for second harmonic generation and a 7mm length of beta-barium borate (BBO) was used for the fourth harmonic generation. The second harmonic generation (SHG) conversion efficiency was 38% (770mW) and the fourth harmonic generation (FHG) efficiency was 26% (200mW). The laser’s spectral linewidth was 95%). However, due to the low absorption cross section normally associated with an alkali-rare gas blue satellite, the original XPAL scheme generally suffers from poor utilization of the pump energy. We report here a novel pumping scheme for XPALs in which the alkali-noble gas mixtures are pumped with two colors, resulting in greater efficiency and an order of magnitude increase in the pump absorption coefficient. Our

+1 360 676 3290 · [email protected]

69

Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX experiments show that synchronous pumping of alkali-noble gas mixtures results in an increase in the overall laser efficiency by at least a factor of 1.7. Also, the effective quantum efficiency of the system is above 100% due to the extraction of 102 cm^-1 of thermal energy per emitted photon. This pumping scheme appears to be applicable to a broad range of alkali-rare gas mixtures. The spectroscopy and kinetics of this new family of lasers will be discussed.

9729-6, Session 1

Wave optics simulation of diode pumped alkali laser (DPAL) (Invited Paper) Masamori Endo, Tokai Univ. (Japan); Ryuji Nagaoka, Hiroki Nagaoka, Toru Nagai, Fumio Wani, Kawasaki Heavy Industries, Ltd. (Japan) A numerical simulation code of diode pumped alkali laser (DPAL) is developed. We have been observing the output power rollover in our Cs DPAL, when Cs partial pressure increases, despite the pump power absorption is better. We expect that a detailed simulation code, considering spatial mode overlap and spectral divergence of the pump light could identify the reason of the problem. The code employs the Fresnel-Kirchhoff diffraction integral for both laser mode and pump light propagations between the resonator mirrors. A three-dimensional atomic-photon rate equations are calculated simultaneously to determine the three-dimensional local gain. Spectral divergence of the pump source is represented by a series of (typically 21) pump lights with different wavelengths, occupying the same volume. Stimulated emission and absorption are calculated for these lines with different cross sections determined by the pressure broadening of the Cs atom. The developed simulation is tested for various operational condition of our small-scale (6.5W) DPAL apparatus. Excellent agreement has been seen in most of the tests. Especially, the agreement of the output power dependence on the focal position of the pump light proves the adequacy of the model. Finally, the roll over the output power has been correctly reproduced. It has been found that the main channel of the pump power drain is the spontaneous emission from the upper level of lasing transition, due to the fairly short (35 ns) life time.

9729-7, Session 1

Measurement of the total ionization rate in an operating Cs DPAL Michael Shaffer, Boris V. Zhdanov, Matthew Rotondaro, Randall Knize, U.S. Air Force Academy (United States) This talk presents the results of experiments on the direct measurement of the ionization rates in an operating continuous wave static Cs DPAL. Ionization occurs due several possible mechanisms including multiphoton processes. In these experiments, stainless steel electrodes were mounted inside the lasing alkali cell and biased by the external voltage source. The collected currents, estimated to be in the nanoampere range, were measured by a PicoAmmeter. We designed and manufactured an alkali vapor cell with AR coated windows and mounted the electrodes inside the cell such that they are parallel to the optical axis of the laser cavity and to the direction of the pump and lasing beams (longitudinal pumping design). The alkali cell was filled with 1 g of metallic Cs and Methane buffer gas at 600 Torr. The cell was temperature controlled and the vapor density was 1.5 x 1013 cm-3. In these experiments, we have collected data for total ionization current as a function of applied bias voltage across the electrodes for different values of incident resonant pump power in the range 3W – 20W with a maximum output laser power about 10W. These values of ionization currents were converted into total ionization rates and compared to values calculated in previous publications.

9729-8, Session 1

Deactivation and reaction of excited states of Rb in collisions with H2, CH4 and C2H6 Valeriy N. Azyazov, Aleksei P. Torbin, Samara State Aerospace Univ. (Russian Federation); Alexander M. Mebel, Florida International Univ. (United States); Sean Bresler, Michael C. Heaven, Emory Univ. (United States) Optically pumped alkali vapor lasers commonly use methane (CH4) or ethane (C2H6) as the agent to induce energy transfer between the optically pumped level (n2P3/2) and the upper laser level (n2P1/2). A complication with this scheme is that the alkali metal eventually reacts with the hydrocarbons, yielding particulate carbon and metal hydrides as contaminants in the gain medium. The reactions of ground state alkali metals with methane and ethane are endothermic, but excitation to the first excited 2P state is sufficient to make the reactions slightly exothermic. This is experimentally verified for the related reaction M(2P)+H2 ? MH + H, and thermodynamic data predict that the reactions of M(2P) with methane and ethane will also be exothermic. We have used laser pump-probe methods to examine the reactions of Rb(n2P) with H2, CH4, and C2H6 for states with n=5, 6, and 7. The H2 reactions were examined to validate the LIF method used for RbH detection. For methane and ethane, pump-probe measurements that examined the Rb(5s) ground state recovery kinetics indicated loss due to reaction following pulsed excitation to the n2P states. Surprisingly, the RbH product was not detected. The results from highlevel ab initio calculations are being used to study the reactive interactions between Rb, methane and ethane.

9729-9, Session 1

Myths, legends and facts; from SDI to tactical battlefield lasers: Reflections of a ‘star warrior’ (Invited Paper) James A. Horkovich, Directed Energy Professional Society (United States) This talk presents a history of missile defense and the “Star Wars” program and its’ evolution to today’s tactical battlefield laser systems, marking the 30th anniversary of President Ronald Reagan’s “Star Wars” speech. Since Archimedes’ “Burning Glass” at the siege of Syracuse 212 B.C. through the development of the LASER man has been fascinated with the idea of using directed energy weapons. But nothing did more to focus this effort than the threat posed by Mutually Assured Destruction. Under Reagan’s “Star Wars” plan years and billions of dollars were invested in making high energy laser systems a reality. This presentation discusses the fundamentals of laser physics and traces the development of these systems in the USA and USSR from the Gas Dynamic LASER laboratory in the 1960s and the USAF Airborne Laser Laboratory of 1981 through the SDI era and up to today. In reflecting on the effort invested in developing this technology, this interdisciplinary talk addresses the role that this technology played in changing the geopolitical state of the cold war and continues to play in international defense efforts today. Note: This talk takes 45 – 50 minutes in its complete form. It is most suited as a plenary or historical talk,

9729-10, Session 2

Laser excitation dynamics of argon metastables generated in atmospheric pressure flows by microwave frequency microplasma arrays Wilson T. Rawlins, Kristin L. Galbally-Kinney, Steven J. Davis, Physical Sciences Inc. (United States); Alan R.

70

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX Hoskinson, Jeffrey A. Hopwood, Tufts Univ. (United States)

9729-13, Session 2

The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkali-exciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at elevated pressure. This paper describes on-going investigations of the use of linear microwave micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure in optical pump-and-probe experiments for laser development. Each array consists of a set of microstrip transmission line resonators with a small (25-100 micron) gap to ground in which the microplasma is ignited. Power requirements to ignite and sustain the plasma at 1 atm are low, 10e12 cm-3) in Ar/He mixtures, at total pressures close to 1 atm, is essential for the efficient operation of an optically pumped Ar* laser. We have used emission spectroscopy and diode laser absorption measurements to observe the production and decay of Ar* in a parallel plate pulsed discharge. With discharge pulses of 1 ?s duration we find that metastable production is dominated by processes occurring within the first 100 ns of the gas break-down. Application of multiple, closely spaced discharge pulses yields insights concerning conditions that favor metastable production. This information has been combined with time-resolved measurements of voltage and current. The experimental results and preliminary model of the discharge kinetics will be presented.

Return to Contents

9729-14, Session 2

Narrow spectral width laser diode for metastable argon atoms pumping Jun Gao, Wuhan National Lab. for Optoelectronics (China); Bin Li, Xinbing Wang, Huazhong Univ. of Science and Technology (China); Duluo Zuo, Wuhan National Lab. for Optoelectronics (China) and Huazhong Univ. of Science and Technology (China) The optically pumped metastable rare gas laser (OPRGL) has attracted more and more attention for its potential to obtain high power laser with good beam quality and atmospheric transmittance. Among all of the rare gases, argon is the cheapest one and the OPRGL using it will be easily conducive to large-scale applications. As the absorption line is an atomic one, the first step for the high power OPRGL of argon is to realize a high power pump source with narrow spectral width emitting around 811.53 nm. Diode laser pump source for OPRGL of argon was realized by employing a complex external cavity coupled with volume Bragg grating (VBG). A commercial available c-mount LD with rated power of 6 W was used. The LD were studied in both the free running mode and VBG external cavity. For the external cavity laser diode, the output beam of LD was collimated by an aspherical lens, and the temperatures of VBG and LD were controlled separately by thermal-electrical-coolers (TEC). A high resolution spectrometer with resolution limit 13 pm near 812 nm was applied to measure the spectra of the output laser beam. Maximum output power of 3.9 W with FWHM less than 25 pm and peak wavelength located around 811.53 nm was obtained. The peak wavelength could be tuned more than 300 pm by precise control of the VBG temperature. These results will benefit the further research on OPRGL of argon.

+1 360 676 3290 · [email protected]

71

Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX

9729-15, Session 3

Optical pumping of the oxygen-iodine laser medium Marsel V. Zagidullin, P.N. Lebedev Physical Institute (Russian Federation); Mikhail S. Malyshev, Samara State Aerospace Univ. (Russian Federation); Valeriy N. Azyazov, Samara State Aerospace Univ. (Russian Federation); Michael C. Heaven, Emory Univ. (United States) The kinetics of the processes in an O2 – I2 – He – H2O gas flow that is irradiated simultaneously by light at wavelengths near 500 nm and 1315 nm, is considered. Radiation at 500 nm is used to photodissociate about 1% of iodine molecules. The radiation at 1315 nm excites atomic iodine to the 2P1/2 state. Singlet oxygen molecules are produced via the energy exchange process I(2P1/2)+O2(3?) ? I(2P3/2) + O2(1?), while I(2P1/2)+O2(1?) energy pooling produces oxygen molecules in 1? state. I(2P1/2) and O2(1?) then accelerate the dissociation of I2. A kinetic analysis was performed for a gas flow at 70 torr pressure, 300 K temperature, 60 W/cm2 500 nm light intensity and 5 kW/cm2 IR irradiation. It is shown that this scheme produces an oxygen – iodine medium with a high degree of iodine dissociation and a relative content of singlet oxygen O2(a1?) exceeding 10 %. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10–2 cm–1 on the 2P1/2 – 2P3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen – iodine laser with this active medium may reach ~100 W cm–2 at an optical efficiency of 60%. If H2O is excluded, which is an active O2(1?) quencher, it is possible to achieve an O2(1?) fraction of up to 70% and inversion of the oxygen b1?=>X3? transition.

9729-16, Session 3

Oxygen assisted iodine atoms production in an RF discharge Pavel A. Mikheyev, Samara State Aerospace Univ. (Russian Federation); Nikolay I. Ufimtsev, P.N. Lebedev Physical Institute (Russian Federation); Andrey V. Demyanov, Troitsk Institute for Innovation and Fusion Research (Russian Federation); Igor V. Kochetov, Valeriy N. Azyazov, P.N. Lebedev Physical Institute (Russian Federation); Anatoly P. Napartovich, Troitsk Institute for Innovation and Fusion Research (Russian Federation); Michael C. Heaven, Emory Univ. (United States) Experiments and modeling of CH3I dissociation in the plasma of a 40 MHz RF discharge were performed. A discharge chamber of an original design, consisting of quartz tubes between two planar electrodes, produced iodine atoms at number densities up to 2?1016 cm 3. Contamination of the walls of the tubes did not impair the discharge stability, providing a good iodine production rate. Addition of oxygen into the Ar:CH3I mixture resulted in a substantial increase in CH3I dissociation efficiency. At a discharge power 200 W, complete CH3I dissociation in Ar:CH3I:O2 mixture was observed. The fraction of discharge power spent on iodine atom production at 0.17 mmol/s CH3I flow rate was 16%. Modeling showed satisfactory agreement with the experiments.

Jensen, General Atomics Aeronautical Systems, Inc. (United States) We report on investigation of novel 2-µm thulium (Tm)–based laser accelerator driver (LAD) offering efficient generation of high-energy pulses with high-peak power at high repletion rate, high efficiency, and with neardiffraction-limited beam quality (BQ). Laser accelerators of nuclear particles by ultrashortpulse laser-generated plasmas offers much reduced size and cost compared to conventional accelerators of the same energy, which would drastically cut the cost of high-energy particle research on colliderbased facilities and advanced light sources, thus replacing the traditional mammoth-size and costly accelerator research facilities with room-size systems [1]. LAD operating at 2 µm wavelength offers ponderomotive force 4x that of 1 µm and 6x that of the traditional 0.8 ?m LAD. In addition, the Tm bandwidth of nearly 400 nm offers >15% tunability and generation of ultrashort pulses down to 20% wall-plug efficiency. This work presents the relative performance of several Tm-doped materials and LAD configurations. Comparisons to traditional 0.8-µm Ti-sapphire and 1-µm Yb lasers are also shown. Experimental data on gain uniformity and thermo-optical distortions are presented. This work was in-part supported by the US Department of Energy Grant Number DE- SC0013762. 1. Proc. of Workshop on Laser Technology for Accelerators, Summary Report, US Department of Energy, January 23-25, 2013

9729-19, Session 4

Effect of laser power on the microstructural behaviour and strength of modified laser deposited Ti6Al4V+Cu alloy for medical application Mutiu F. Erinosho, Esther T. Akinlabi, Univ. of Johannesburg (South Africa) The excellent biocompatibility property of Grade 5 titanium alloy has made its desirability largely increasing in the field of biomedical. The titanium alloy (Ti6Al4V) was modified with the addition of 3 weight percent (wt %) copper via a laser deposition process using the Ytterbium fiber laser with a wavelength of 1.047 µm. Therefore, this paper presents the effect of laser power on the microstructural behaviour and strength of the modified Ti6Al4V+Cu alloy. The laser powers were varied between 600 W and 1600 W respectively while all other parameters such as the scanning speed, powder flow rates and gas flow rates were kept constant. The melt pool and width of the deposited alloy increases as the laser power was increased. The ?-lamella was observed to be finer at low laser power, and towards the fusion zone, Widmanstettan structures were fused and become smaller; and showing an evidence of ?-martensite phases. The strength of the modified alloy was derived from the hardness values. The strength was observed to increase initially to a point as the laser power increases and afterwards decreased as the laser power was further increased. The improved Ti6Al4V+Cu alloy can be anticipated for biomedical application.

9729-20, Session 4

High pulse energy 1123nm laser of Nd:GdLuAG mixed garnet medium

9729-18, Session 4

Wide-bandwidth Tm-based amplifier for laser acceleration driver

Yang Liu, Zhaojun Liu, Sasa Zhang, Jinbao Xia, Yanmin Zhang, Chen Guan, Shandong Univ. (China)

Drew A. Copeland, John Vetrovec, Amardeep S. Litt, Aqwest, LLC (United States); Joseph M. Fukumoto, Steven

Diode-pumped CW and passively Q-switched lasers of Nd:GdLuAG mixed garnet at 1123 nm were demonstrated. The maximum average output power of CW operation was 4.13 W. For Q-switched operation, the average output

72

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9729: High Energy/Average Power Lasers and Intense Beam Applications IX power was 800 mW, the corresponding single pulse energy was 133.8 µJ. The Nd:GdLuAG laser emitting at 1123 nm was obtained for the first time to the best of our knowledge, which proves that the Nd:GdLuAG mixed garnet has a better ability of energy storage than Nd:YAG in 1123 nm oscillation.

9729-21, Session PTue

Lidar for monitoring methane emission in Siberian permafrost Alexsandr S. Grishkanich, Aleksandr Zhevlakov, Sergey Kascheev, ITMO Univ. (Russian Federation); Igor Sidorov, Univ. of Eastern Finland (Finland); Valentin Elizarov, ITMO Univ. (Russian Federation); Andrey Mak, National Research Univ ITMO (Russian Federation) Over the past 10 years the rate of temperature in the Siberia increases almost twice higher than the average rate of warming of the planet. Identifying methane anomalies responsible for the temperature increase, by hiking trails in the Arctic requires great human labor. It is necessary to use lidar methods for search and identification of methane from permafrost. Necessary to create a Raman lidar for monitoring of emissions of methane hydrate from the permafrost. Hyperspectral resolution would resolve the isotope shifts in the Stokes spectra, thereby to determine the isotopic composition of methane ratio C14/C12 CH4 carbon emissions and identify the source for study (permafrost or oil deposits) Isotopic composition of the methane (concentration of 13C, 14C and D) can provide information concerning the methane origin and formation time. Analysis of the concentration of radioactive isotope 14C allows discerning methane fractions with biological and abiological origins. Isotope 14C appears in the atmosphere due to the cosmic rays. The interaction of nitrogen 14N nuclei with neutrons from the cosmic rays transforms them into the 14C isotope nuclei. Half life of the 14C isotope is 5 730 years, which is significantly exceeds lifetime of absolute majority of Earth life forms. Later on radioactive carbon nuclei emit electron and once again become a stable isotopes 14N. Carbon isotope 14C interacts with the atmospheric oxygen by forming molecules of carbon dioxide 14CO2. Later these molecules along with the ones of the stable carbon isotope 12CO2 are included into the processes of the living organic matter formation trough the photosynthesis. Automated airborne lidar will allow estimation of the methane emissions intensity, as well as evaluation of qualitative and quantitative parameters of of the methane anomalies.

Return to Contents

9729-22, Session PTue

The control of CO2 lasing temporal characteristics by modulated self-injected irradiation Vadim V. Kiyko, A. M. Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation) and ITMO Univ. (Russian Federation); Danil Mikhaylov, A. M. Prokhorov General Physics Institute of the Russian Academy of Sciences (Russian Federation) A modified theoretical model of CO2 laser supplemend with selfinjection of laser output irradiation to unstable cavity is presented. It is based on classical one-dimensional six-temperature model. The model is supplemented with terms that consider influence from self-injected irradiation by external optical system that selects and returns portion of output irradiation. The self-injection influence on static and dynamic parameters of laser system was studied. Also, the dynamic of lasing with temporal modulated self-injection was studied. It is shown that returning even small part of the output irradiation and its amplification in an active medium radically changes dynamic parameters of laser. It is demonstrated that with temporal modulation of self-injection it is possible to obtain the lasing mode similar to Q-switch by output parameters (like as pulse shape and duration). Despite similar output parameters, dynamical processes in laser cavity in Q-switched mode and temporal modulated self-injected mode are completely different. A significant influence on the output characteristics of the laser can be obtained by controlling power an order of magnitude less than the output power of the laser. For example, the numerical simulation showed that with self-injecting power near 5% of laser output power could be obtained the pulse-periodical lasing mode with pulse duration near 300 ns, pulse repetitive rate 20 kHz and peak-to-average power relation near 20. The numerical results have been experimentally verified. During the experiments the lasing mode was changed from CW to pulse-periodical with parameters close to mentioned above with temporal modulated self-injection only.

+1 360 676 3290 · [email protected]

73

Conference 9730: Components and Packaging for Laser Systems II Tuesday - Thursday 16–18 February 2016 Part of Proceedings of SPIE Vol. 9730 Components and Packaging for Laser Systems II

9730-1, Session 1

Integrated disruptive components for 2µm fibre lasers (ISLA): project overview and passive component development (Invited Paper) Gary Stevens, Tom Legg, Gooch & Housego (Torquay) Ltd. (United Kingdom); Peter Shardlow, ORC, University of Southampton (United Kingdom) In this presentation, an overview of the EU FP7 project ISLA (Integrated disruptive componentS for 2 µm fibre Lasers) is given. The aim of ISLA was to develop a set of “building block” components and a “tool-kit” of processes to define an integrated modular common platform for two micron fibre lasers consisting of compatible and self-consistent active and passive fibres, fused fibre couplers and combiners, fibre-coupled isolators, modulators and high power pump laser diodes. We also present results from our work on developing passive components for 2 µm fibre lasers. This includes high power pump combiners that have been tested up to 0.5 kW and combiners for in-band pumping of holmium lasers. Couplers for use as splitters, power monitors and wavelength division multiplexers have also been demonstrated. Wide-band couplers, with a coupling ratio that only varies ± 12% over 400 nm, have also been developed to exploit the wide tuning range possible with thulium fibre lasers. Research into different isolator materials was also conducted to find materials with large Verdet constants to be used in 2 µm isolators. Fibrecoupled isolators were then manufactured using a selection of these materials. Isolators that had insertion losses of < 1 dB and isolation of > 35 dB were demonstrated using PM and non-PM fibres. In the PM isolators, PER > 23 dB was achieved.

9730-2, Session 1

Acousto-optic devices for operation with 2µm fibre lasers Jon D. Ward, Gooch & Housego PLC (United Kingdom); Gary Stevens, Gooch & Housego (Torquay) Ltd. (United Kingdom); Peter C. Shardlow, Univ. of Southampton (United Kingdom) Fibre lasers operating in the 2µm region are of increasing interest for a range of applications, including laser machining and biomedical systems. Fibre laser manufacturers were able to call upon enabling technologies used by the telecoms industry when developing lasers at 1µm & 1·5µm, but at longer wavelengths, for example 2µm, many such components are either unavailable or immature. We report on recent developments of Acousto-Optic Modulators/ Frequency-Shifters and Tunable Filters that are specifically optimised for use with fibre systems operating at or around 2µm. AO devices are interesting due their ability to conserve spatial-coherence making them appropriate for use with single-mode optical fibres. We describe how choice of interaction medium is an important consideration, particularly affecting the drive power and the polarisation behaviour of the device – the latter being an important parameter when used in a fibre system. We also describe two designs of AO Tunable Filter intended for laser tuning. Both designs have been demonstrated intracavity in 2µm fibre lasers. The first gives exceptionally narrow resolution (??/? 99.9%T) and very high laser damage thresholds (100 J/cm2) at 1.06 µm for silica windows with ARSS. In this paper we will present results for MILSPEC durability tests on silica windows both with and without ARSS that were conducted at a government facility, involving rain and sand erosion as well as salt fog testing. Results will be reported using a variety of test conditions, such as variable impact speeds and angles of incidence. In light of these results, we will discuss their utility as exit apertures in high energy laser systems.

Return to Contents

+1 360 676 3290 · [email protected]

85

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV Monday - Wednesday 15–17 February 2016 Part of Proceedings of SPIE Vol. 9731 Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV

9731-1, Session 1

Self-stabilized 3-5 µm frequency comb based on frequency-divide-by-two GaAs OPO (Invited Paper) Kevin F. Lee, Christian Mohr, Jie Jiang, IMRA America, Inc. (United States); Peter G. Schunemann, BAE Systems (United States); Konstantin L. Vodopyanov, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States); Martin E Fermann, IMRA America, Inc. (United States) Degenerate optical parametric oscillators (OPOs) divide optical frequencies by two with only modest pumping. This makes them promising mid-infrared frequency comb sources. Our measurements show that our degenerate OPO preserves the frequency comb stability of the pump to sub-Hz levels. However, degenerate OPOs are often overlooked due to their interferometric cavity stabilization requirements. We find that the stability requirements of our system are actually much simpler, because thermal feedback results in self-stabilization. When the OPO is oscillating, absorption of the intracavity field increases the crystal temperature, and subsequently the effective cavity length, which is fortunately the right direction to stabilize degenerate oscillation in our system. Our OPO is based on an orientation-patterned GaAs crystal, pumped by a stabilized 2 W, 418 MHz, optically-referenced Tm frequency comb, generating a broadband, mid-infrared frequency comb centered at 4 µm. We have observed continuous OPO oscillation for almost an hour without cavity length feedback. These measurements show that a degenerate OPO can serve as a simple device to downconvert a frequency comb.

9731-2, Session 1

Octave-wide frequency comb centered at 4 µm based on a subharmonic OPO with Hz-level relative linewidth Viktor O. Smolski, Jia Xu, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States); Peter G. Schunemann, BAE Systems (United States); Konstantin L. Vodopyanov, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States) We study coherence properties of a more-than-octave-wide (2.5-7.5 µm) mid-IR frequency comb based on a 2-µm Tm-fiber-laser-pumped degenerate (subharmonic) optical parametric oscillator (OPO) that uses orientation-patterned gallium arsenide (OP-GaAs) as gain element. By varying intracavity dispersion, we observed a ‘phase’ transition from a single-comb state (at exactly OPO degeneracy) to a two-comb state (neardegenerate operation), characterized by two spectrally overlapping combs (signal and idler) with distinct carrier-envelope offset frequencies. We achieve this by generating a supercontinuum (SC) from the mode-locked Tm laser that spans most of the near-IR range, and observing RF beats between the SC and parasitic sum-frequency light (pump + OPO) that also falls into the near-IR. We found RF linewidth to be 200 mW) we boost the power of the laser with a tapered amplifier in a master-oscillator power-amplifier configuration [2] and use either bulk or planar-waveguide crystals for second harmonic generation. This - especially for the planar-waveguide crystal - much more complex setup offers higher power and better linewidth as we use an optical isolator to shield the laser from back-reflections here. At the conference we will present a theoretical analysis of the expected performance of the different setups and compare the results with the results of our experimental analysis. [1] Paschke, K.; Wenzel, H.; Fiebig, C.; Blume, G.; Bugge, F.; Fricke, J. and Erbert, G., “High Brightness, Narrow Bandwidth DBR Diode Lasers at 1120 nm”, IEEE Photonics Technology Letters., vol. 25, , pp. 1951-1954 (2013) [2] Spießberger, S.; Schiemangk, M.; Sahm, A.; Wicht, A.; Wenzel, H.; Peters, A.; Erbert, G. and Tränkle, G., “Micro-integrated 1 Watt semiconductor laser system with a linewidth of 3.6kHz”,Optics Express, vol. 19, , pp. 7077-7083 (2011)

9731-9, Session 3

Compact deep UV laser system at 222.5 nm by single-pass frequency doubling of high-power GaN diode laser emission Norman Ruhnke, André Müller, Bernd Eppich, Reiner Güther, Martin Maiwald, Bernd Sumpf, Götz Erbert, Günther Tränkle, Ferdinand-Braun-Institut (Germany) Deep ultraviolet (DUV) lasers emitting below 300 nm are of great interest for many applications, for instance in medical diagnostics or for detecting biological agents. Established DUV lasers, e.g. gas lasers or frequency quadrupled solid-state lasers, are relatively bulky and have high power consumptions. A compact and reliable laser diode based system emitting in the DUV could help to address applications in environments where a portable and robust light source with low power consumption is needed. In this work, a compact DUV laser system based on single-pass frequency doubling of high-power GaN diode laser emission is presented. A commercially available high-power GaN laser diode from OSRAM Opto Semiconductors serves as a pump source. The laser diode is spectrally stabilized in an external cavity diode laser (ECDL) setup in Littrow configuration. The ECDL system reaches a maximum optical output power of 700 mW, maintaining narrowband emission below 60 pm (FWHM) at 445 nm over the entire operating range. By direct single-pass frequency doubling in a BBO crystal with a length of 7.5 mm a maximum DUV output power of 16 ?W at a wavelength of 222.5 nm is generated. The presented concept enables compact and efficient diode laser based light sources emitting in the DUV spectral range that are potentially suitable for field applications where small footprint and low power consumption is essential.

9731-10, Session 4

Mid-IR Kerr-lens mode-locked polycrystalline Cr:ZnS and Cr:ZnSe lasers with intracavity frequency conversion via random quasi-phase-matching (Invited Paper) Sergey Vasilyev, Igor S. Moskalev, Mikhail S. Mirov, IPG

88

Photonics - Mid-Infrared Lasers (United States); Viktor Smolski, IPG Photonics Mid Infrared Lasers (United States); Sergey B. Mirov, IPG Photonics - Mid-Infrared Lasers (United States) and The Univ. of Alabama at Birmingham (United States); Valentin P. Gapontsev, IPG Photonics Corp. (United States) Cr2+ doped polycrystalline ZnS and ZnSe possess a unique blend of physical, spectroscopic, and technological parameters. Four-level energy structure, broad vibronic emission bands, absence of excited-state absorption, and close to 100% quantum efficiency of fluorescence enable room-temperature mid-IR lasers with power in excess of 50 W and a broad tuning range (1.9 – 3.3 µm). Kerr-lens mode-locked polycrystalline Cr2+:ZnS lasers with up to 2 W average power and 6. In this work we examined the effect of V/III ratio, growth rate, and growth temperature on domain propagation in OP-GaAs and OP-GaP. Maximum thickness and resulting OPO/DFG performance will be reported.

9731-13, Session 4

Frequency conversion efficiency in freestanding periodically oriented gallium nitride Christopher G. Brown, Univ. Research Foundation (United States); Steven R. Bowman, Jennifer K. Hite, Jaime A. Freitas, Francis J. Kub, Charles R. Eddy Jr., Igor Vurgaftman, Jerry R. Meyer, U.S. Naval Research Lab. (United States); Jacob H. Leach, Kevin Udwary, Kyma Technologies, Inc. (United States) Gallium Nitride’s (GaN) material properties of broadband transparency, high thermal conductivity, and wide-band gap make it a promising candidate for high power frequency conversion devices. GaN possesses a nonlinear susceptibility similar in magnitude to lithium niobate, due to strong internal polarization, but conventional phase matching is prevented due to GaN’s weak birefringence. In order to obtain efficient nonlinear optic frequency conversion, patterned inversion growth has been developed to induce quasi-phase matching (QPM). We have fabricated and tested periodically oriented gallium nitride (PO-GaN) devices in order to obtain QPM frequency conversion. We report recent measurements of second harmonic generation, free carrier absorption, bulk scattering losses, and absorption due to unintentionally doped impurities.

Return to Contents

9731-14, Session 5

Homo and heteroepitaxial growth and study of orientation-patterned GaP for nonlinear frequency conversion devices Vladimr L. Tassev, Rita D. Peterson, Shivashankar Vangala, Michael Snure, Martin Kimani, Air Force Research Lab. (United States) Frequency conversion in orientation-patterned (OP) materials is a leading approach for generating tunable mid- and long-wave coherent infrared radiation for a wide variety of applications. The strong interest led to intensive investigation of a number of nonlinear optical materials. GaP is an especially promising material, due to its unique properties—high nonlinear susceptibility, low two-photon absorption in the convenient pumping range 1–1.7 µm and high thermal conductivity. Growth of OPGaP has encountered several challenges, such as relatively low quality of commercially available GaP wafers, and uncontrollable parasitic nucleation that reduces the growth rate and the layer quality, especially during longer runs. Here we describe an original approach for producing thick, high-quality OPGaP with excellent domain fidelity via a one-step HVPE homo or heteroepitaxial growth process with growth rate of about 100 µm/h. Two-inch wafer bonded OPGaP templates and templates in which polarity alternation was achieved in a MBE assisted procedure were used. AFM, SEM, XRD, EDS and TEM showed smooth surface morphology and high crystalline quality, while optical characterization confirmed substantial reduction of the 2-4 µm absorption typical for all n-type GaP samples, low 2PA (??≤ 0.1 cm/GW, compare with 15-16 cm/GW for GaAs) and low optical losses. Important crystallographic considerations on how to avoid the appearance of (111)p facet that could overgrow the pattern, and why alternating the polarity may favor the growth near the interface are also provided.

9731-15, Session 5

Linear and nonlinear optical properties of GaAs and GaP grown using hydride vapor phase epitaxy Shekhar Guha, Air Force Research Lab. (United States); Jean Wei, Joel M. Murray, Jacob O. Barnes, Air Force Research Lab. (United States) and UES, Inc. (United States); Peter G. Schunemann, BAE Systems (United States) Frequency doubling, tripling and quadrupling of carbon dioxide lasers operating in the 9.2 to 10.8 ?m wavelength range provide the means to generate tunable radiation in the 4.6 to 5.4 ?m, 3.1 to 3.6 ?m and 2.3 to 2.7 ?m wavelength ranges, respectively. Orientation patterned GaAs and GaP are promising nonlinear optical materials for these processes because of their high nonlinearity and low absorption at the relevant wavelengths. In order to calculate the expected conversion efficiencies, one must have an accurate knowledge of the material d coefficient for these interactions at each wavelength. Along with the dispersion of the refractive indices, it is also important to know the wavelength and temperature dependence of the absorption coefficient of the materials. In the infrared spectral range, neither the wavelength dependence of the d coefficient value nor the temperature and wavelength dependence of the absorption coefficients of GaAs and GaP are readily available. We have therefore undertaken a detailed study to determine these values. The absorption coefficients of crystals grown by the hydride vapor phase epitaxy (HVPE) process have been measured over a temperature range of 77 K to 295 K for the 1 to 20 µm wavelength range and compared with materials grown from melt and slow cooling. Using a picosecond laser tunable in the 2 to 10 µm wavelength range, the values of the d coefficient were measured using HVPE-grown single crystals.

+1 360 676 3290 · [email protected]

89

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV

9731-16, Session 5

9731-46, Session 5

Determination of the type II phasetransition region in random relaxor ferroelectrics using Cherenkov secondharmonic microscopy

Nonlinear refraction dynamics of solvents and gases (Keynote Presentation)

Mousa Ayoub, Hannes Futterlieb, Jörg Imbrock, Cornelia Denz, Westfälische Wilhelms-Univ. Münster (Germany) Ferroelectrics are pivotal materials in devices for sensor applications, data storage, and selective optical parametric processes. Methods for the accurate characterization of these materials regarding the dynamics of their growth and switching are critical in the exploration and understanding of the outstanding properties for technological developments. This complex dynamics has been well studied by past work. However, how the phase transition of relaxor ferroelectrics in fact takes place is still under active debate. The combination of the measurements of the characteristics, achieved until now with, the visualization in the volume is still an open requirement. In this contribution we demonstrate the first three-dimensional monitoring of the evolution of the spontaneous polarization (Ps) during transition from the para- to ferroelectric phase and vice versa. This allows us to determine the Curie temperature range more accurately, what is required for relaxor ferroelectrics. The monitoring is based on a key sensitive feature to the domain wall. This is optically provided by Cherenkov-type secondharmonic microscopy. Here we identify chronologically the dimension of the evolution process. The microscopic measurements are combined with second-harmonic measurements in far field. The medium studied here, is a relaxor random strontium barium niobate (SBN), in which Ps is represented by 3D needle-like objects (several hundreds of micrometers in length). The quantitative value of Ps is recorded simultaneously by measuring the poling current. Our results pave the way for deeper understanding of the ferroelectric nature for more accurate modeling of this complex behavior that is fundamental for all applications of ferroelectrics.

9731-17, Session 5

Optical limiting properties of carbon disulfide at 2.05 ?m wavelength Lars G. Holmen, Magnus W. Haakestad, Norwegian Defence Research Establishment (Norway) Several types of infrared sensors are based on sensitive focal plane arrays. In such sensors, the intensity will typically increase by a factor 10^7 at the focal plane, compared to the intensity of the incoming radiation. Such arrays are thus vulnerable when illuminated with high-intensity laser pulses. One solution for protecting the array against such pulses is to use an optical limiter, which is a passive device that blocks radiation with high intensity and transmits radiation with low intensity. We here present results where carbon disulfide (CS2) has been tested as an optical limiting material when illuminated with 25 ns pulses with up to several hundred mJ energy at 2.05 µm wavelength. The laser had a beam quality M^2=1.5, and the beam was focused onto a CS2-cell using a lens with an effective f-number of 10 and a focal length of 50 mm. The light emerging from the CS2 cell was refocused onto an aperture, with a field of view of 1.4 mrad. Pulse energies of up to 150 mJ were incident on the cell, while at most 0.6 mJ was transmitted through the aperture, due to dielectric breakdown and beam filamentation in the CS2 cell at high pulse energies. In addition, the nonlinear index of refraction of CS2 at 2.05 µm wavelength was measured using the z-scan technique, yielding a value of (2.8±1.0)•10^(-18) m^2/W. To our knowledge, these are the first optical limiting experiments performed at 2 ?m wavelength using CS2.

90

Eric W. Van Stryland, Peng Zhao, Trenton Ensley, Matthew C. Reichert, David J. Hagan, CREOL, The College of Optics and Photonics, Univ. of Central Florida (United States) We use our recently developed femtosecond excitation-probe beamdeflection (BD) method to measure the temporal dynamics of nonlinear refraction in various liquids and gases for different polarization combinations. This allows us to determine the temporal response function of these materials. In turn, this allows us to predict the outcome of other experiments, e.g. Z-scan, as a function of the pulsewidth used. For gases, the coherent revivals reveal the IR rotational spectrum including changes in line-width with rotational quantum number. Comparisons can also be made between the second hyperpolarizability in liquid and gas phase.

9731-18, Session 6

High-power mid-infrared high repetition rate supercontinuum source based on a chalcogenide step-index fiber Stefan Kedenburg, Tobias R. J. Steinle, Florian Mörz, Andy Steinmann, Harald Giessen, Univ. Stuttgart (Germany) We demonstrate a tunable and robust femtosecond supercontinuum source with a maximum output power of 550 mW and a maximum spectral width of up to 2.0 ?m which can cover the mid-infrared region from 2.3 ?m up to 4.9 ?m by tuning the pump wavelength. As light source we use a synchronously pumped fiber-feedback OPO and a subsequent OPA which delivers femtosecond, Watt level idler pulses tunable between 2.5 ?m and 4.1 ?m. These pulses are launched into As2S3 chalcogenide step-index fibers with core diameters of 7 and 9 ?m. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy owing to its high brilliance as demonstrated for the CS2-absorption bands around 3.5 ?m.

9731-19, Session 6

Experimental study of supercontinuum generation in an amplifier based on an Yb3+ doped nonlinear photonic crystal fiber Tobias Baselt, Christopher Taudt, Fraunhofer IWS Dresden (Germany) and Westsächsische Hochschule Zwickau (Germany) and TU Dresden (Germany); Bryan Nelsen, Westsächsische Hochschule Zwickau (Germany); AndrésFabián Lasagni, Fraunhofer IWS Dresden (Germany) and TU Dresden (Germany); Peter Hartmann, Westsächsische Hochschule Zwickau (Germany) and Fraunhofer IWS Dresden (Germany) The use of supercontinuum light sources in different optical measurement methods, like microscopy or optical coherence tomography, has increased significantly compared to classical wideband light sources. The development of various optical measurement techniques benefits from the high brightness and bandwidth, as well as the spatial coherence of these sources. For some applications, only a portion of the broad spectral range

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV can be used. Therefore, an increase of the spectral power density in limited spectral regions would provide a clear advantage over spectral filtering. This study describes a method to increase the spectral power density of supercontinuum sources by amplifying the excitation wavelength inside a nonlinear photonic crystal fiber (PCF). An ytterbium doped photonic crystal fiber was manufactured by a sol-gel process and used in a fiber amplifier setup as the nonlinear fiber medium. In order to characterize the fiber’s optimum operational characteristics, group-velocity dispersion (GVD) measurements were performed on the fiber during the amplification process. For this purpose, a notch-pass mirror was used to launch the radiation of a stabilized laser diode at 976 nm into the fiber sample for pumping. The performance of the fiber was compared with a conventional PCF. Finally, the system as a whole was characterized in reference to common solid state-laser-based photonic supercontinuum light sources. An improvement of the power density up to five times was observed between 1030 nm to 1350 nm wavelengths.

sensitive detection system. Due to the high reflectivity of the cavity mirrors, the beam experiences a long effective optical path length resulting in large absorption values and allowing to achieve detection at very low concentrations. If the mirrors reflectivity is high over a large spectral region, the technique allows the simultaneous detection of gases that exhibits absorption lines in different wavelength ranges. A supercontinuum source which possesses high brightness over a very large bandwidth and which is perfectly spatially coherent is therefore ideal to exploit the full potential of the method. Here, using a compact supercontinuum source we demonstrate for the first time multi-components gas detection of acetylene and methane with high sensitivity in the mid-infrared, over a bandwidth extending from 3000 to 3500 nm. These results are significant not only because they illustrate the potential of incoherent supercontinuum sources for spectroscopy in the mid-infrared but also because they represent the largest continuous detection window reported so far.

9731-35, Session PTue

9731-20, Session 6

All-normal dispersion supercontinuum generation in the near-infrared by Raman conversion in standard optical fiber Christophe Louot, Erwan Capitaine, Badr M. Shalaby, Katarzyna Krupa, Alessandro Tonello, Dominique Pagnoux, Claire Lefort, Philippe Leproux, Vincent Couderc, XLIM Institut de Recherche (France) Coherent Raman spectroscopy methods like coherent anti-Stokes Raman scattering (CARS) or stimulated Raman scattering (SRS) can be implemented by using a monochromatic pump wave and a broadband Stokes wave. In the case of 1064 nm pumping, a Stokes spectrum extending up to 1600 nm is required in order to probe chemical bonds from the fingerprint area to the CH stretching region. This broadband spectrum has to be particularly flat, with the highest possible spectral power density. Usually, such spectrum is obtained by means of supercontinuum generation in a solid-core photonic crystal fiber, which is operated in the anomalous dispersion regime. Here we demonstrate all-normal dispersion supercontinuum generation in the 1080-1600 nm range by propagating sub-nanosecond pulses in a high numerical aperture standard optical fiber (Corning HI 980, with zero dispersion wavelength at 1600 nm). The extreme saturation of the Raman gain provides a flat spectrum in the considered range, making this broadband source particularly suitable for coherent Raman spectroscopy. The unusual regime of supercontinuum generation, i.e. Raman gain saturation regime, is highlighted. It is investigated through a complete numerical and experimental spectrotemporal study, and the corresponding results are compared with those obtained from a photonic crystal fiber. Finally the possibility of operating spectrometer-free timeresolved coherent Raman spectroscopy is introduced.

9731-21, Session 6

Novel efficient high power parametric THz source based on QPM nonlinear crystal fiber Pengxiang Liu, Wei Shi, Degang Xu, Tianjin Univ. (China); Nasser N. Peyghambarian, The Univ. of Arizona (United States) We proposed a novel GaAs-based crystal fiber configuration for efficient THz difference frequency generation (DFG), which combines the singlemode THz fiber and the quasi-phase-matching for DFG THz generation. Calculations were performed on the characteristics of energy conversion and output beam focusing. Theoretical results indicated that the proposed THz crystal fiber structure can provide high power and high brightness THz radiation. The output power, spectral power density and brightness are also analyzed, based on the calculation of the dynamic of energy conversion and the characteristics of the THz beam focusing. High output power (average ~1 W) and excellent focusing characteristic allow us to achieve THz generation with high brightness (100 MW/(sr•cm2)), a promising value for many applications.

9731-36, Session PTue

Walk-off free 266 nm generation of freely triggerable 60 ps pulses in periodically poled LBGO Thomas Schoenau, Dietmar Klemme, Romano Haertel, Kristian Lauritsen, Rainer Erdmann, PicoQuant GmbH (Germany)

Caroline Amiot, Piotr Ryczkowski, Antti Aalto, Juha Toivonen, Goëry Genty, Tampere Univ. of Technology (Finland)

Laser pulses from diode based laser systems in the UV range are of great interest in the fields of microscopy and spectroscopy. Providing UV wavelength pulses at variable repetition frequencies or on demand requires nonlinear frequency conversion in single pass arrangement with a crystal featuring a high effective nonlinear coefficient. In the past, such devices based on borate materials (e.g. BBO, CLBO) suffer intrinsically from walk-off due to the phase-matching condition. As a result, extensive efforts had to be made to obtain a clean transverse mode without distortion at the expense of induced power loss.

The measurement of gas concentration is paramount in many industrial applications ranging from emission control to chemical reaction optimization. Many gases of interest possess very strong absorption lines in the mid-infrared; in fact stronger than in any of other spectral regions. Incoherent broadband cavity enhanced absorption spectroscopy is a simple and robust method for the detection of gases with high sensitivity. In this technique a broadband source is coupled to a high-finesse confocal cavity filled with gas and the transmitted light is analyzed with a wavelength-

Our approach presented here utilized the newly available PP-LBGO device with 2nd-order quasi-phase matching (QPM) to obtain a walk-off free and undistorted fundamental transverse mode. We investigated and compared the conversion efficiency of PP-LBGO with a classic beta-BBO crystal and measured the beam quality. The pump laser is based on a 1064 nm distributed feedback (DFB) gain-switched seed laser diode and two-stage fiber amplifier. After second harmonic generation to 532 nm the light is focused into the PP-LBGO for single pass generation of 266 nm. Since the

Multi-component gas detection in the midinfrared with supercontinuum

Return to Contents

+1 360 676 3290 · [email protected]

91

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV PP-LBGO is non-hygroscopic, the material is easy to handle and a long life time is expected and under investigation. The target power level of 1 mW average power at 80 MHz is sufficient for a wide range of applications in the life sciences, such as fluorescence spectroscopy and confocal microscopy.

9731-37, Session PTue

Pulsed 266 nm laser based on fiber laser source for sensing application Junji Hirohashi, Yasuhiro Tomihari, Satoshi Makio, Yasunori Furukawa, Oxide Corp. (Japan); Marc Le Flohic, Keopsys SA (France) Forth harmonic (266 nm) laser was demonstrated based on pulsed fiber laser combined with frequency convertor for sensing application. Fundamental 1064 nm laser was fiber based laser with?repetition rate of 50 kHz, peak power of 25 kW, pulse width of 1 ns and average power of 1 W. The light was delivered by polarization maintain large mode area fiber and connected to the frequency convertor. In the frequency convertor, second harmonic 532 nm was generated by PP-Mg:SLT with more than 50% of conversion efficiency without walk-off and then forth harmonic 266 nm was generated by BBO with 30% of conversion efficiency. Both frequency conversion devices were operated at 40 degree-C. The 266 nm with average power of more than 150 mW was confirmed with stable operation. Since the output properties of relatively high repetition rate and high peak power, it is suitable for sensing application from the point of better signal noise ratio and measurement speed. In addition, since the combination of this fiber laser head and frequency convertor with simple single pass configuration, it is possible to realize affordable laser module for easy to integrate into the portable sensing system such as LIDAR systems. The shorter wavelength such as 266 nm could be attractive to characterize much smaller particle sensing comparing to the visible or IR sensing systems.

9731-38, Session PTue

Stimulated polariton scattering in KTA crystal and its application in tunable stokes laser generation Jie Zang, Zhenhua Cong, Xiaohan Chen, Xingyu Zhang, Zengguang Qin, Zhaojun Liu, Jianren Lu, Shandong Univ. (China); Shiqi Jiang, Shandong Univ. (China); Qiang Fu, Dong Wu, Shandong Univ. (China) The stimulated polariton scattering (SPS) is a nonlinear process in which the second- and third-order nonlinear effects are involved. The essential condition for SPS in a crystal is the existence of one or more intense transverse optical A1 modes which are both infrared- and Raman-active. In the process of the SPS, three waves including the pumping wave, the generated Stokes wave and the polariton wave interact in the overlapped beam area. The momentum conservation and energy conservation must be satisfied simultaneously. The SPS can be used to generate tunable terahertz wave and tunable Stokes laser emission near the pumping wavelength. SPS can occur in a few crystals. Potassium titanyl arsenate (KTiOAsO4, KTA) is one of them. This paper presents the tunable Stokes laser characteristics based on the SPS in KTA crystal. The pumping source is a 1064.2 nm Q-switched laser. The pulse energy, pulse width, repetition rate and beam size are 125 mJ, 10 ns, 10 Hz and 3.5 mm, respectively. The tenability is realized by adjusting the angle between the pumping beam and the Stokes laser cavity axis. When the angle is changed from 1.875° to 6.500°, five tunable ranges from 1077.9 to 1079.0 nm, from 1080.1 to 1080.8 nm, from 1082.8 to 1083.6 nm, from 1085.5 to 1085.8 nm, from 1086.8 to 1088.4 nm are obtained. The maximum pulse energy is 24.7 mJ obtained at the wavelength of 1078.6 nm.

92

9731-39, Session PTue

Polarization study of a supercontinuum light source for different wavelengths through a photonic crystal fiber Julian M. Estudillo-Ayala, Jose D. Filoteo-Razo, Juan Carlos Hernández-Garcia, Univ. de Guanajuato (Mexico); Jesus Pablo Lauterio-Cruz, Ctr. de Investigaciones en Óptica, A.C. (Mexico); Daniel Jáuregui-Vázquez, Univ. de Guanajuato (Mexico); Baldemar Ibarra-Escamilla, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico); Oliver J. M. Pottiez, Ctr. de Investigaciones en Óptica, A.C. (Mexico); Roberto Rojas-Laguna, Univ. de Guanajuato (Mexico); Evgeny A. Kuzin, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico) In this work we show the changes of polarization at different wavelengths in the end of a photonic crystal fiber (PCF) by means bandpass filters in a supercontinuum light source. A linear and circular polarization was introduced in a piece of PCF, showing the changes of the polarization for each wavelength of each one of the filters from 450 to 700nm. We used a microchip laser as pumping source with wavelength of 532nm and short pulses least than 1 ns with repetition rate of 9KHz. We obtained a continuous spectrum in the visible spectral region. We show a comparison of the polarization state at the fiber input with respect to polarization state in the fiber output for different wavelengths by rotating the axes of the PCF.

9731-40, Session PTue

2 nm continuously tunable 488nm microintegrated diode-laser-based SHG light source for Raman spectroscopy Marcel Braune, Martin Maiwald, Bernd Sumpf, Günther Tränkle, Ferdinand-Braun-Institut (Germany) Raman spectroscopy in the visible spectral range is of great interest due to resonant enhancement of signals in organic samples. Nevertheless, fluorescence and background signals can mask these lines. Shifted Excitation Raman Difference Spectroscopy is a potential tool to overcome this distortion. To apply this method, a dual wavelength light source is necessary. The distance between these two wavelengths should be approximately the spectral width of the bands under study. In this work, a micro-integrated SHG light source emitting at 488 nm with a continuous tuning range up to 2 nm (83 cm-1) and without moving parts is presented. With this feature the SERDS distance between the excitation wavelengths can be adjusted according to the target. The pump source, a DFB laser emitting at 976 nm, and a PPLN waveguide crystal are directly mounted on a micro-Peltier-element. Due to the comparable temperature tuning of laser (66 pm/K) and crystal (72 pm/K), by changing the common temperature from 15°C to 72°C and slight adjustment of laser current (4 pm/mA), the above mentioned tuning range is achieved. An approximately constant 488 nm output power of about 27 mW was measured over the whole spectral range. At lower temperatures, the output power reaches 30 mW. With increasing temperature due to the decrease of the pump power, the SHG power deteriorates with -0.1 mW/K. Moreover, the concept delivers a suppression of the amplified spontaneous emission by the SHG crystal. The use of bandpass-filters is therefore not necessary. A wider SERDS distance becomes easily feasible.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV

9731-41, Session PTue

Phase-matching properties of GaS0.4Se0.6 for type-2 DFG in the 100.41030.6µm range Kiyoshi Kato, Chitose Institute of Science and Technology (Japan); Valentin P. Petrov, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); Nobuhiro Umemura, Chitose Institute of Science and Technology (Japan) Although we reported the Sellmeier equations for GaSxSe1-x (x=0, 0.09, 0.40, and 1.0) that provide excellent reproduction of the phase-matching conditions for harmonic generation of a CO2 laser at 10.5910µm [Kato and Mikami, Appl. Opt., 53, 2177(2014)], the birefringence of GaSe and GaS at 1THz given by these Sellmeier equations are about 0.38 and 0.34 smaller than the experimental values of Zhang et al. [J. Appl. Spectroscopy, 77, 850(2011)] and Molloy et al. [CrystEngComm., 16, 1995(2014)], respectively. In order to construct the accurate Sellmeier equations for GaSxSe1-x in the THz range, we measured the phase-matching angles for type-2 DFG between a Nd:YAG laser and BBO/OPO in a c-cut 4.7-mm-thick GaS0.4Se0.6 crystal at 100.4-1030.6µm. These data were used to refine the Sellmeier equations for GaSxSe1-x in the THz range. By using these Sellmeier equations for GaSxSe1- x (0?x?0.40), we calculated the phase-matching conditions for the near-IR to THz frequency conversion achieved by Nazarov et al. [Appl. Phys. Lett., 99, 081105(2011) and 100, 136104(2012)]. For GaS0.29Se0.71 pumped by a Ti:Al2O3 laser at 0.797µm, our index formula gives the type-1 phase-matching angle of ?ext=7.86º for generating the 1.8THz radiation, which agrees well with their experimental value of ?ext=8º. While, for the same crystal pumped at 0.790µm, our formula gives the eee-type phase-matching angle of??ext=45.0º for generating the 1THz radiation and the refractive index mismatch of |ne, gr(?, ?)-ne(?, ?)|=0.1096, which agree with their experimental values of ?ext=45º and |ne,gr(?, ?)-ne(?, ?)|=0.12. Thus, the utility of our Sellmeier equations for GaSxSe1-x is demonstrated.

9731-42, Session PTue

Studying an advanced regime of the noncollinear two-phonon light scattering for applications to the optical spectrum analysis Alexandre S. Shcherbakov, Adan O. Arellanes, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico) Principally new features of the non-collinear two-phonon light scattering governed by elastic waves of finite amplitude in birefringent bulk crystals are detected and observed. The main goals of our investigations are to reveal novel important details inherent in the nonlinearity of this effect and to study properties of similar parametric nonlinearity both theoretically and experimentally in wide-aperture crystals with moderate linear acoustic attenuation. An additional degree of freedom represented by the dispersive birefringence factor, which can be distinguished within this nonlinear phenomenon, is characterized. This physical degree of freedom gives us a one-of-a-kind opportunity to apply the strongly non-linear two-phonon light scattering in practice for the first time. The local unit-level maxima in the distribution of light scattered into the second order appear periodically as the acoustic power density grows. It makes possible to identify a few transfer function profiles peculiar to these maxima in the isolated planes of angular-frequency mismatches. These maxima give us an opportunity to choose the desirable profile for the transfer function at the fixed angle of incidence for the incoming light beam with a wide spectrum .The needed theoretical analysis is developed and proof-of-principle experiments,

Return to Contents

performed with a specially designed wide-aperture acousto-optical cell made of the calomel (?-Hg2Cl2) crystal, are presented. The obtained spectral resolution ~0.235 Å at 405 nm (i.e. the resolving power ~17,200) can be compared with the most advanced acousto-optical spectrometers for space/airborne operations. Evidently, our results with the calomel-based acousto-optical cell look like the best we can mention at the moment.

9731-43, Session PTue

Thermal study of second harmonic generation in periodically poled crystals Alphonse L. Rasoloniaina, Rodolphe Collin, Christelle Pareige, Ecole Nationale Supérieure des Sciences Appliquées et de Technologie (France); Stéphane Balac, Univ. de Rennes 1 (France); Thierry Chartier, Ecole Nationale Supérieure des Sciences Appliquées et de Technologie (France); Pascal Besnard, CNRS-Fonctions Optiques pour les Technologeis de l’information (France); Alain Mugnier, David Pureur, Quantel Group (France) High-power green lasers present a great interest for many applications such as DNA sequencing, ophthalmology, biotechnology or laser Doppler velocimetry. Second-harmonic generation (SHG) based on quasi-phase matching (QPM) technique presents some advantages such as compactness, high conversion efficiency and high beam quality. In QPM technique, a precise control of crystal temperature is required to obtain the optimum conversion. However, for high powers, thermal effects due to fundamental harmonic (1064 nm) absorption, second harmonic (532 nm) absorption and green induced infrared absorption (GRIIRA) become non-negligible. Temperature gradient takes place and leads to a local variation of the index of refraction. The phase matching becomes temperature dependent and this limits the efficiency. In this case, an active temperature control of the crystal is needed to compensate this phenomenon. In this work, we propose both theoretical and experimental studies of continuous-wave second-harmonic generation in a periodically-poled congruent lithium niobate crystal doped with a magnesium oxide crystal (MgO:PPLN). The temperature distribution in the crystal is obtained by solving: (i) the propagation equations for the fundamental harmonic and second harmonic by a split-step Fourier method and (ii) heat transfer equation by finite elements method where the longitudinal and transverse variations of temperature are taken into account. We present a comparison between theoretical simulations and experimental results. A good agreement with the experiment is observed in term of temperature acceptance or temperature control. Second harmonic generation up to 2.5 W of output power is achieved in 25 mm long crystal.

9731-44, Session PTue

Third-harmonic generation in metallodielectric stacks Han Li, Joseph W. Haus, Partha P. Banerjee, Univ. of Dayton (United States) We examine the problem of third-harmonic generation (THG) in a thin film stack fabricated from multiple layers of metal and dielectric thin films, also called a metallodielectric [1]. We apply the transfer matrix method extended to cover obliquely incident fields [2] to the problem of third-harmonic generation. Due to interference and evanescent field penetration through the metal layers the transmission is much higher than for a single thick metal film. Specifically, we examine THG using silver layers sandwiched between a relatively high index dielectric (around a value of 2), such as tantalum pentoxide or zinc oxide. The THG simulations are an extension of the method developed in Ref. [2] where second-harmonic generation was examined. In the metallodielectric case we use realistic dielectric materials

+1 360 676 3290 · [email protected]

93

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV data and a complex third-order nonlinear coefficient of the metal. The reflected and transmitted third-harmonic efficiencies are optimized by varying each layer thickness within experimentally reasonable limits and by changing the angle of incidence of the pump wave. Further THG metallodielectrics using metals such as copper and gold, as well as selected dielectric materials, will be examined using the same methodology. The comparison between the various metallodielectrics will be made with recommendations for experimental studies.

9731-45, Session PTue

Surface states of silicon crystalline films detected by nonlinear optical laser spectroscopy Dmitry E Milovzorov, Fluens Technology Group Ltd. (Russian Federation) Resonant second-harmonic generation by nanocrystalline silicon films was studied by using optical spectroscopy for a different polarization schemes for incident laser and output radiation. The morphology of films is different for any of them: rectangular crystals in the film with average nanocrystals size 9.7 nm and irregular for the film with nanocrystal size 16.1 nm. There is a differences in resonant spectral peaks positions: 3.22 eV and 3.31 eV for the silicon film with nanocrystal size 9.7 nm; and 3.2 eV and 3,26 eV for the silicon film with nanocrystal size 16.1 nm. SHG spectra show the resonance sharp peaks which is related to the defect or surface states in band gap of silicon. From the rigid surface the optical nonlinear response on second harmonic can be described as stochastic value that can be estimated as nonlinrar function of fundamental laser intensity multiplied on coefficient on nonlinear transformation of radiation and correlation function between added field fractions generated by various parts of rigid films.

9731-22, Session 7

Delivering kilojoules of pre-heat to fusion targets in Sandia’s Z-Machine: Or why do we care about nonlinearities in laser-plasma interactions? (Keynote Presentation) Matthias Geissel, Adam J. Harvey-Thomson, Thomas J. Awe, Sandia National Labs. (United States); Michael E. Campbell, Lab. for Laser Energetics (United States); Matthew R. Gomez, Eric Harding, Christopher Jennings, Mark W. Kimmel, Patrick F. Knapp, Sandia National Labs. (United States); Sean M. Lewis, The Univ. of Texas at Austin (United States); Kyle Peterson, Marius Schollmeier, Adam B. Sefkow, Jonathon E. Shores, Daniel B. Sinars, Stephen A. Slutz, Ian C. Smith, Christopher S. Speas, Roger A. Vesey, John L. Porter, Sandia National Labs. (United States) Sandia National Laboratories pursues a novel concept of inertial confinement fusion that includes a pre-magnetization of the fuel. The ‘Magnetized Liner Inertial Fusion’ concept heats up deuterium untilizing the Z-Beamlet laser while exposed to a magnetic field and subsequently implodes fuel using the ‘Z’ pulsed power facility. While the interaction of lasers with matter is well understood for processes at kilowatt power levels, the pre-heat process in MagLIF reaches terawatt powers and intensities beyond 10^14 W/cm?, which are subject to complex and largely nonlinear phenomena. A thin solid density window covers the laser entrance hole to confine the fuel initially, and a pre-pulse decompresses it below the critical plasma density, enabling propagation into the fuel. However, there are

94

nonlinear processes at lower densities that compromise energy coupling or cause energy deposition in undesirable locations. Dominant processes are scattering on ion-acoustic waves (Stimulated Brillouin Scattering), scattering on electron-plasma waves (Stimulated Raman Scattering), or two-plasmon decay. These are complex instabilities that require advanced computer simulations even for approximate predictions of the problems being caused by them. We will discuss laser-plasma instabilities (LPI), measurement techniques such as near beam imaging, and methods to minimize these instabilities using beam smoothing techniques. Measurements for various levels of LPI will illustrate the progress made at Sandia in order to advance the efforts in magneto-inertial fusion. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

9731-23, Session 7

Efficient cascaded generation of narrowband linearly-polarized radiation in random Raman fiber laser Sergey A. Babin, Ekaterina A. Zlobina, Sergey I. Kablukov, Evgeniy V. Podivilov, Institute of Automation and Electrometry (Russian Federation) Random Raman lasers attract now a great deal of attention as they operate in non-active turbid or transparent scattering media. In the last case, singlemode fibers with feedback via Rayleigh backscattering are used to generate high-quality directed laser beam with relatively narrow modeless spectrum. However, generation in such random Raman fiber lasers (RRFLs) is limited in polarization properties: the light is usually depolarized or has unstable polarization, even for the first Stokes wave. Here we demonstrate a linearly-polarized cascaded random Raman lasing in a PM fiber with polarized pumping. Quantum efficiency of converting input pump radiation (1.05?m) into the 1st (1.11?m), 2nd (1.17?m) and 3rdorder (1.23?m) Stokes waves amounts to 79%, 83%, and 77%, respectively. Taking that the passive losses at propagation of pump radiation in the fiber are ~15%, almost all pump photons are converted into the generated Stokes wave, regardless of the order. Herewith, polarization extinction ratio (PER) is as high as >22 dB for all the waves at powers up to ~10 W. The laser bandwidth grows with increasing Stokes order, but it is almost independent on the generated power varying in the range of 0.8-1.3nm, 1.4-2.3nm and 2.4-3.3nm for the consecutive orders, respectively. At that, the generated spectrum remains to be sufficiently narrower than the Raman gain profile. An analytical model has been developed describing well the generated power and spectrum for all components of the cascaded RRFL. The unique features of such source with a potential of broad-range tuning offer new opportunities in applications.

9731-24, Session 7

Temporal characterization of a multiwavelength hybrid Brillouin-erbium fiber laser Victor L. Lambin-Iezzi, Ecole Polytechnique de Montréal (Canada); Thomas F. S. Büttner, Ctr. for Ultrahigh bandwidth Devices for Optical Systems (Australia); Amirhossein Tehranchi, Sébastien Loranger, Ecole Polytechnique de Montréal (Canada); Irina V. Kabakova, Benjamin J. Eggleton, The Univ. of Sydney (Australia); Raman Kashyap, Ecole Polytechnique de Montréal (Canada)

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV We have investigated hybrid Multi-Wavelength Brillouin and erbium fiber lasers (MWBEFL) which are particularly interesting because of their simplicity, robustness, their only need for components, low power threshold, high tunability and their ability to generate a large number of Brillouin shifted frequencies. Their basic principle is to combine the narrow nonlinear gain offered by SBS in an undoped fiber with the broadband linear gain from an erbium doped fiber to enable the cascaded process of SBS. These lasers represent a convenient way for generating multi-wavelengths with comb-like optical spectra that have a frequency channel spacing equal to the Brillouin frequency shift ~10 GHz or multiple of it. Numerous configurations for MWBEFLs have been suggested over the years, but their characterization has been limited to optical and radio-frequency spectral measurements. Here, we provide a detailed temporal characterization of several MWBEFL configurations by measuring the optical power of the single frequency channels with high temporal resolution. It is found that the power in each channel is highly unstable due to the excitation of several cavity modes. We also provide real-time measurements for a configuration that was reported to emit phase-locked picosecond pulse trains, concluded from autocorrelation measurements [1]. The real-time measurements reveal a high degree of instability without the formation of stable pulse trains. References: [1] S. Loranger, V. L. Iezzi, and R. Kashyap, “Demonstration of an ultra-high frequency picosecond pulse generator using an SBS frequency comb and self phase-locking,” Opt. Express, vol. 20, pp. 19455-19462, 2012.

9731-25, Session 7

Compact silica-fiber Brillouin laser with highly damped intensity-noise Schadrac Fresnel, Stéphane Trebaol, Yohann Léguillon, Christelle Pareige, Pascal Besnard, Ecole Nationale Supérieure des Sciences Appliquées et de Technologie (France); Sophie LaRochelle, Univ. Laval (Canada) Compact and low-cost coherent sources are needed to improve system performances of sensors and telecommunication systems, e.g. in coherent optical communication links and microwave photonic applications. Brillouin fiber lasers (BFLs) have been attracting a lot of interest lately due to their very narrow linewidth and very low relative intensity noise (RIN) and frequency noise (FN). Indeed, the first Stokes component (S1) generated by a pump can have more than 6 dB RIN-reduction compared to the pump. Furthermore, its FN can be reduced by 10-20 dB, depending on the pump characteristics and on the packaging of the Brillouin laser. We have already shown an 8 dB reduction (above the theoretical 6 dB-limit) in S1-RIN using a compact chalcogenide BFL with two Stokes orders. This can be explained by the fact that, above the second order threshold, the lasing S1 component is saturated leading to a compression of its intensity noise. In this paper we examine robust and compact silica BFLs with improved noise properties. Since single frequency operation is mandatory to achieve coherent sources, the Free Spectral Range of the laser cavity has to be higher than the Brillouin gain-bandwidth or, in other words, a short cavity length has to be employed (< 20 m). We designed a 16.66 m-long polarization-maintaining silica-fiber cavity (FSR = 12 MHz) with a 10 dBm threshold for S1, 15 dBm for the second-order component S2, and 18 dBm for S3. Operating above the S2 threshold, we show a severe damping of the S1 RIN of 20 dB, while maintaining a FN reduction of 10 dB, compared to that of the pump.

9731-26, Session 7

Mid-infrared, external cavity BaWO4 Raman laser at 2602 nm with 1.25-W output power Onur Kuzucu, ASELSAN Inc. (Turkey) An external cavity BaWO4 Raman source pumped by a Q-switched Ho:YAG

Return to Contents

laser is demonstrated. Average output power level of 1.25 W is generated at the first Stokes wavelength of 2602 nm for 9.7 W incident pump power. Output pulse widths as short as 19 ns was measured at a repetition rate of 6.67 kHz. Near-diffraction limited beam quality is observed (M2=1.25). This simplified Raman laser configuration can harness the high average power levels offered by Thulium- and Holmium-doped solid-state and fiber lasers to generate fixed-wavelength and tunable output at 2.3-2.8 um.

9731-27, Session 8

Designing non-trivial QPM spectral shapes in Titanium in-diffused PPLN (Invited Paper) Alexander V. Sergienko, Boston Univ. (United States) Integrated optics based on lithium niobate offers the versatility of multifunctional devices connected by channel waveguides on a single substrate. The enabling technology is the diffusion of lithographically defined titanium stripes into lithium niobate resulting in the formation of low loss channel waveguides. Combined with quasi-phase matching induced by electric field poling this leads to non-linear frequency convertion of exceptional efficiency. The distinct advantage of Ti in-diffused waveguides is that both Type I and Type II phase matching processes are allowed by a suitable choice of the poling period. Moreover, the low optical background facilitates the quantum frequency conversion of polarization-encoded photonic qubits with high fidelity. The careful design of poling period together with the waveguide geometry allows controlling the transverse mode structure of the qubits. Additional flexibility in the poling profile design permits the tailoring of phase matching spectrum. A quasi-rectangular flat-top or Gaussian spectrum as broad as 200 nm is designed by chirping and apodization of the poling period. We discuss applications of such devices to quantum frequency conversion of temporal qdits, which has been proposed for higher dimensional encoding of quantum information, and mid-infrared chip-scale frequency combs generation by frequency down conversion of commercially available Er combs at 1550 nm. Additional constraints imposed on quasi-phase matching would allow control over spectral phase as well. We discuss extended phase matching conditions in the context of generating frequency-correlated photon pairs by spontaneous parametric down conversion.

9731-28, Session 8

Broadband wavelength control for optical parametric oscillation in radially-poled whispering gallery resonators Sarah-Katharina Meisenheimer, Univ. of Freiburg (Germany) and Fraunhofer-Institut für Physikalische Messtechnik (Germany); Josef U. Fürst, Univ. of Freiburg (Germany); Annelie Schiller, University of Freiburg (Germany); Karsten Buse, Fraunhofer-Institut für Physikalische Messtechnik (Germany) and Univ. of Freiburg (Germany); Ingo Breunig, Univ. of Freiburg (Germany) Optical parametric oscillators (OPOs) provide tunable continuous-wave coherent light for, e.g., infrared spectroscopy. In such current OPO-based systems, typically light of a pump laser with a wavelength of about 1 µm is down-converted by a periodically-poled lithium niobate crystal placed inside a mirror cavity. Whispering gallery resonators (WGRs) are promising cavities for miniaturizing the current OPO setup. However, identification of the whispering gallery modes and controlled tuning of wavelengths over a wide spectral range are essential and still challenging for employing OPOs in WGRs for infrared spectroscopy. In this work, we demonstrate that identification of the whispering gallery modes of pump, signal, and idler light can be achieved by comparing experimental data to simulations

+1 360 676 3290 · [email protected]

95

Conference 9731: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications XV for both, the pump spectrum and the tuning behavior of the OPOs. For controlled tuning of the output wavelengths over a wide infrared spectral range (1.7–2.5 µm), a whispering gallery pump mode with selected radial and polar mode numbers is addressed. The pump wavelength and these mode numbers are kept fixed while increasing the temperature of the crystal in well-defined steps, going from one longitudinal mode to the next. This provides wider and more reliable tuning than it has been achieved before. Experimental data showing mode identification, improved tuning and the applicability to spectroscopy are presented for a calligraphically poled WGR with 2 mm diameter and 28 µm domain period length, being suitable for quasi phase matching of 1.04 µm pump light.

9731-29, Session 8

Broadly tunable OPGaAs OPO pumped by Cr:ZnSe laser Rita D. Peterson, Gary Cook, Air Force Research Lab. (United States) Coherent sources that are broadly and continuously tunable in the mid- and longwave infrared are of interest for a variety of scientific, commercial, and military applications. The advantages in an OPO of quasi-phasematched materials like orientation-patterned gallium arsenide (OPGaAs) come at the cost of the angle tuning possible in birefringent nonlinear crystals. Temperature tuning is limited by the material’s dn/dT value, and lacks speed and stability. A better alternative is to tune the OPO by tuning the pump laser. Here we report an OPGaAs OPO pumped by a gain-switched Cr:ZnSe laser which was continuously tuned by an intracavity etalon. The etalon also narrowed the output linewidth to 2 nm. The Cr:ZnSe laser operated at a repetition rate of 500 Hz with a 25 ns pulsewidth. The pump was focused to a spot size (1/e^2) of 100 µm at the center of a simple linear resonator formed by two 5-cm ROC mirrors. The OPGaAs crystal was 14 mm long, with a period of 97 µm, and was mounted with no active cooling. Tuning the pump laser over a range of 90 nm (2385-2475 nm) produced OPO output over a range of almost 4.5 µm (3500-7450 nm). OPO tuning was ultimately limited by coatings on the crystals and the resonator mirrors, as the Cr:ZnSe laser is capable of much broader tuning as a pump source. A maximum slope efficiency of 21% was obtained, with a pulse energy threshold of 93 µJ.

9731-30, Session 8

High-repetition rate, picosecond-pulse, tunable, mid-IR PPLN OPG source Yelena Isyanova, Wenyan Tian, Q-Peak, Inc. (United States); Peter F. Moulton, MIT Lincoln Lab. (United States) We report here on the performance of a narrow-line, mid-IR source based on a PPLN-crystal optical parametric generator (OPG). The PPLN crystal was pumped by a pulsed, 20-MHz-rate, 1064-nm Yb:fiber-based source operating with 20-psec pulses and average output power of 20 W. Prior to achieving the parametric generation, we built an optical parametric amplifier (OPA). We used a 2051-nm diode with output power of 0.8 mW as a seed source for the OPA. The 2-cm long PPLN crystal with the 31.1 ?m poling period was placed in a high-temperature oven at 137 deg. C. We achieved the OPA and OPG threshold at 17 W and 18 W of pump power, respectively. Since the average output power of the OPG was low, we replaced the 2-cm crystal with the 5-cm one with the same grating period. With this crystal, the OPG threshold was observed at 5.2 W of pump power. Seeding was not necessary and did not affect the performance of the OPG. The maximum output power measured was 0.55 W. The OPG produced a broad spectrum between 2027 nm and 2239 nm. Since we were interested in producing a narrow, 1mm) nonlinear medium for adequate signal strength. This ordinarily proves highly problematic due to so-called longitudinal geometrical smearing effects. We solved this problem by imparting significant pulse-front tilt onto the reference pulse and simultaneously using a particular beam-crossing angle that precisely cancels out the geometrical smearing. This conveniently also increased the delay range, increasing the maximum measurable pulse length. With this technique, we were able to measure complex supercontinua on a single shot for the first time. We will discuss this technique and these measurements, as well as other issues important to measuring such pulses.

9732-9, Session 2

Roguescope: Real-time high-throughput spectroscopy at 100 million frames per second Mohammad H. Asghari, Univ. of California, Los Angeles (United States); Paul Trinh, Time Photonics Inc. (United States); Bahram Jalali, Univ. of California, Los Angeles (United States) The real-time measurement of fast non-repetitive events is arguably the most challenging problem in the field of instrumentation and measurement. These instruments are needed for investigating rapid transient phenomena such as chemical reactions, fast physical phenomena, phase transitions, protein dynamics in living cells and impairments in data networks. Optical spectrometers are the basic instrument for performing sensing and detection in chemistry, physics and biology applications. Unfortunately, the scan rate of a spectrometer is often too long compared with the timescale of the physical processes of interest. In terms of conventional optical spectroscopy, this temporal mismatch means that the instrument is too slow to perform real-time single-shot spectroscopic measurements. Single-shot measurement tools such as frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are, although powerful, therefore unable to perform pulseresolved spectral measurements in real time. Roguescope is a commercially available single-shot optical spectrometer with a frame rate of up to 100 Million frames per second, at least one thousand times faster than the next fastest spectrometer. The Roguescope real-time capability is enabled by photonic time-stretch implemented by Time-Stretch Dispersive Fourier Transform. The Roguescope can capture large data sets to reveal rare events with meaningful accuracy. Applications include optical rouge waves, laser transients, chemical reactions, and nonlinear dynamics. RogueScope is an essential tool for measurements of fast stochastic processes such as laser transients, rare events and outliers in optical systems. RogueScope is ideal for capturing non-Gaussian statistics that are signatures of complex dynamics.

100

9732-10, Session 2

Towards pattern generation and chaotic series prediction with photonic reservoir computers Piotr Antonik, Michiel Hermans, François Duport, Marc Hälterman, Serge Massar, Univ. Libre de Bruxelles (Belgium) Reservoir Computing is a bio-inspired computing paradigm for processing time dependent signals that is particularly well suited for analog implementations. Our team has demonstrated several photonic reservoir computer with performance comparable to digital algorithms on a series of benchmark tasks such as channel equalisation and speech recognition. Recently, we showed that our opto-electronic reservoir computer could be trained online with a simple gradient descent algorithm programmed on an FPGA chip. This setup makes it in principle possible to feed the output signal back into the reservoir, and thus highly enrich the dynamics of the system. This will allow to tackle in hardware complex prediction tasks, such as pattern generation, chaotic and financial series prediction, that have so far only been studied in digital implementations. Here we report simulation results of our opto-electronic setup with FPGA chip and output feedback applied to pattern generation and Mackey-Glass chaotic series prediction. The simulations take into account the major aspects of our experimental setup. We find that pattern generation can be easily implemented on the current setup with very good results. The Mackey-Glass series prediction task is more complex and requires a large reservoir and more elaborate training algorithm. With these adjustments promising result are obtained, and we now know what improvements are needed to match previously reported numerical results. These simulation results will serve as basis of comparison for experiments we will carry out in the coming months.

9732-11, Session 2

Real-time characterization of spectral coherence of ultrafast laser based on optical time-stretch Yiqing Xu, Xiaoming Wei, Zhibo Ren, Kenneth K. Y. Wong, Kevin Tsia, The Univ. of Hong Kong (Hong Kong, China) Nonlinearly generated broadband ultrafast laser have been increasingly utilized in many applications. However, traditional techniques of characterizing these sources lack the ability to observe the instantaneous features and transitory behaviours of both amplitude and phase. With the advent of the optical time stretch techniques, the instantaneous shotto-shot spectral intensity can be directly measured continuously at an unprecedentedly high speed. Meanwhile, the information of the real-time phase variation, which is carried by the frequency-time mapped spectral signal has yet been fully explored. We present a technique of experimentally measuring the spectral coherence dynamics of broadband pulsed sources. Our method relies on a delayed Young’s type interferometer combined with optical time-stretch. We perform the proof-of-principle demonstrations of spectral coherence dynamic measurement on two sources: a supercontinuum source and a fiber ring buffered cavity source, both with a repetition rate of MHz. By employing the optical time stretch with a dispersive fiber, we directly map the spectral interference fringes of the delayed neighbouring pulses and obtain a sufficiently large ensemble of spectral interferograms with a real-time oscilloscope (80Gb/s sampling rate). This enables us to directly quantify the spectral coherence dynamics of the ultrafast sources with a temporal resolution down to microseconds. Having the ensemble of singleshot interferograms, we also further calculate the cross spectral coherence correlation matrices of these ultrafast sources. We anticipate that our technique provides a general approach for experimentally evaluating the spectral coherence dynamics of ultrafast laser generated by the nonlinear processes e.g., modulation instability, supercontinuum generation, and Kerr resonator.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9732: Real-time Measurements, Rogue Events, and Emerging Applications

9732-12, Session 2

9732-14, Session 3

Dissipative temporal solitons in an excitable micropillar laser with integrated saturable absorber and delayed feedback

Convective Nozaki-Bekki holes in a long laser

Sylvain Barbay, Félix Lelièvre, Ali Golestani, Foued Selmi, Rémy Braive, Grégoire Beaudoin, Isabelle Sagnes, Lab. de Photonique et de Nanostructures (France) A micropillar laser with integrated saturable absorber and delayed feedback is shown experimentally and theoretically to sustain controllable trains of dissipative temporal solitons controlled by adequate optical perturbations in the excitable regime. We show that the pulse train can be started or resynchronized (retiming) with a single perturbation and that the system can store a large variety of temporal pulse patterns. We discuss the relevance of the various timescales at stake for such functionalities. Besides its interest as a compact source of controllable pulses that can be arranged if needed in arrays, this system has also interesting potential for neuromimetic processing of information since it can be considered as a leaky-integrate-and-fire (LIF) optical neuron with delayed feedback. The LIF neuron model is a widespread model in neuroscience and in neurocomputing models and as such it is at the foundation of neural networks, a promising avenue for alternative computation systems.

9732-13, Session 3

Periodic wave-trains, supercontinuum generation and the formation of rogue waves in an optical fiber cavity (Invited Paper) Majid Taki, Zheng Liu, Saliya Coulibaly, Univ. des Sciences et Technologies de Lille (France); François Léo, Univ. Libre de Bruxelles (Belgium) We study analytically, numerically and experimentally the spontaneous formation of dissipative periodic solutions in a coherently driven passive optical fiber cavity under Raman effect and third-order dispersion. It is shown that the latter, that breaks the time-reversal symmetry, affects the bifurcation nature, at onset of the instability, leading to a transition from a sub- to a super-critical bifurcation. The analytical description of this bifurcation demonstrates an original dependence of the nonlinear saturation term upon the third-order dispersion. A striking feature is the existence of an optimal nonlinear resonance leading the maximum asymmetry in the spectrum. Our theory reveals the key role of third-order dispersion on the asymmetry in the spectrum of the dissipative structures, explains early observations, and the predictions are in excellent agreement with our experimental findings. In the strongly nonlinear regime, Eckhaus instabilities characterize the secondary instabilities where stable propagating dissipative wave-trains are generated with a definite frequency and a constant group velocity. Their stability range is enlarged in the presence of the third-order dispersion, which determines completely their group velocity. An increasing in the injected pump value leads to transitions from periodic wave trains to chaotic regimes with a continuous spectrum and the appearance of rogue waves in the form of abnormal high amplitudes. We have analytically characterized this transition and determined the transition curves from regular to chaotic regimes where supercontinuum and rogue waves may occur.

Return to Contents

Svetlana Slepneva, Tyndall National Institute (Ireland); Ben O’Shaughnessy, Cork Institute of Technology (Ireland) and Tydall National Institute (Ireland); Stephen P. Hegarty, Cork Institute of Technology (Ireland) and Tyndall National Institute (Ireland); Bryan Kelleher, Univ. College Cork (Ireland); Sergio Rica, Univ. Adolfo Ibáñez (Chile); Guillaume Huyet, Cork Institute of Technology (Ireland) and Tyndall National Institute (Ireland) We investigate both theoretically and experimentally the properties of a 20km long unidirectional fiber ring cavity laser that includes a semiconductor optical amplifier and a tunable Fabry-Perot filter. The laser displays turbulent dynamics when the filter transmission is set at a wavelength longer than 1320nm since the laser operates in a self-focusing regime. At lower wavelengths the laser displays multistability between cw and turbulent regimes. We investigate the stability of these solutions both numerically and experimentally by controlling the value of detuning, which is the frequency mismatch between the filter driving frequency and the cavity roundtrip frequency. For the decreasing detuning, the cw solution becomes unstable leading to the appearance of turbulent emission. For the increasing detuning, a subcritical bifurcation occurs, leading to the stabilisation of another cw solution via a turbulent regime. To further investigate the dynamics of this regime, we drive the filter in resonance with the laser round trip frequency. This regime, referred to as Fourier Domain Mode-Locking (FDML), is commonly used to design high-frequency swept sources since the entire sweep is stored in the cavity. It is also worthwhile to notice the analogy with a one dimensional system with a spatiallyvarying detuning. In such a case, we observe the formation of cw and turbulent domains and near the subcritical bifurcation point, we observe the continuous formation of convective turbulent domains that grow and merge into one turbulent region. A detailed analysis shows that these domains emerge from the cw solution by first creating Nozaki-Bekki holes.

9732-15, Session 3

Levy statistics and rare events in random laser emission Ravitej Uppu, Tata Institute of Fundamental Research (India) and Univ. Twente (Netherlands); Sushil A. Mujumdar, Tata Institute of Fundamental Research (India) Random lasers are intriguing complex systems that have proven to be a rich testbed of unique statistical studies. Based on the interplay of optical gain and light diffusion [1], the inherent randomness in these systems manifests several fluctuations, including the realization of non-Gaussian heavy-tailed intensity distributions. One puzzling phenomenon observed from these apparently ‘dirty’ systems is the genesis of first-order temporally coherent peaks in the emission spectrum. The high intensities of these peaks constitute the outliers in an otherwise well-behaved distribution. The origin of coherent emission in these systems has recently been modeled using a novel platform of exponentially tempered Lévy sums [2]. The underlying Lévy variables correspond to the amplified spontaneous emission photons that diffuse through multiple scattering. The exponentially-tempered Levy sum model was shown to accurately capture the strong intensity fluctuations. These strong fluctuations in the sums signify strong fluctuations of the extreme values in the summands, i.e. the Lévy variables. Here, we explore the importance of these rare extreme summands in determining the fluctuations in the Lévy sums. Further, we investigate the effect of tempering on the rarity of these extreme summands to explain the Lévy to Gaussian crossover in the statistics of sums. Careful experimental analysis along with detailed photon transport

+1 360 676 3290 · [email protected]

101

Conference 9732: Real-time Measurements, Rogue Events, and Emerging Applications

[2] R. Uppu, and S. Mujumdar, Phys. Rev. Lett., 114, 183903 (2015)

Finally, we will discuss how the spectral dynamics, i.e. instantaneous spectrum at each cavity round-trip, could be measured in fiber lasers generating irregular train of pulses of quasi-CW radiaton via combination of heterodyning and intensity spatio-temporal measurement concept. Using this method, we will reveal the existence quasi-stationary localizes lasing modes in the radiation of random fibre laser.

9732-16, Session 3

9732-18, Session 4

Spatiotemporal chaos induces extreme events in a spatially extended microcavity laser

Caustics, rogue waves and an optical sea

Monte Carlo simulations signify the importance of rare extreme summands in determining the statistical nature of the intensity fluctuations in random laser emission. [1] D.S. Wiersma, Nat. Phys., 4, 359 (2008)

Sylvain Barbay, Lab. de Photonique et de Nanostructures (France); Saliya Coulibaly, Lab. de Physique des Lasers, Atomes et Molécules (France); Foued Selmi, Lab. de Photonique et de Nanostructures (France); Marcel G. Clerc, Univ. de Chile (Chile) Extreme and rare events are ubiquitous in nature. They are characterized by rare and high amplitude excursions of a given variable characterizing a physical system with respect to its long time average. The study of extreme events and extreme waves in optics has been primarily motivated by the analogy with rogue waves in hydrodynamics whose formation mechanism is still not well understood but include ingredients such as spatial instabilities, nonlinearities and noise. Here we consider a spatially extended microcavity laser with integrated saturable absorber in the self-pulsing regime. This system has two advantages: first, its typical timescales are fast enough to allow large recordings in a small amount of time and hence to allow for accurate statistics. Second and even more important, it does not display irregular or aperiodic dynamics and hence extreme events without spatial coupling. Hence we can really study the role of spatial coupling in the emergence of extreme events. By recording the dynamics simultaneously in two different spatial points we are able to study whether the extreme events occur through a mechanism of coherent structure collision, as already reported in different systems. With the help of a mathematical model, linear stability and numerical analysis of the dynamics we unveil the dynamical origin of the extreme events found in the occurrence of spatiotremporal chaos rather than in the merging dynamics of coherent structures. The understanding of the formation mechanism of these extreme phenomena is an important step to devise strategies to control them.

Rogue waves are statistically rare events with extreme amplitude or intensity which have been observed in numerous physical systems. In optics particularly, the study of rogue waves has provided new insights into the dynamics of noise-induced soliton propagation during supercontinuum generation. Most studies have focused on how nonlinearity can lead to rogue-wave behavior, but we report here an experimental demonstration of optical rogue waves in a purely linear system which yields a 2D random spatial “sea” of coherent radiation. The experiments are based on free space propagation of a random spatial phase applied via spatial light modulator. By varying the nature of the applied random phase pattern, we are able to see the development of random caustics in the propagating field that yield large amplitude events that satisfy the “significant wave height” criteria of rogue waves. To validate this analogy, we performed optical phase retrieval techniques on the propagating field to extract the amplitude from the intensity distribution – amplitude, not intensity, being relevant in an oceanic context. Additional results show the clear relationship between the width of the spatial spectrum and the emergence of rogue wave events. Indeed, slightly non-Gaussian spectra with high-frequency content but no strong focusing were tested, significantly modifying the statistics of events. These results from optics confirm previous studies of the possible role of caustics in ocean wave dynamics, and provide further evidence that purely linear mechanisms cannot be discounted when studying rogue wave generation mechanisms.

9732-19, Session 4

Slow deterministic vector rogue waves

9732-17, Session 4

Spatio-temporal intensity dynamics of passively mode-locked fiber laser (Invited Paper) Dmitry V. Churkin, Aston Univ. (United Kingdom); Srikanth Sugavanam, Aston University (United Kingdom) Usually lasers are thought to be operated in some temporal regime. In our work we experimentally show that a laser could be operated in a distinct, albeit complex and dynamic spatio-temporal regime. Different spatio-temporal regimes could have different periodicity properties over different scales, i.e. different spatio-temporal patterns could emerge. We will demonstrate the methodology of real-time measurements of intensity spatio-temporal dynamics on an example of passively mode-locked fibre laser generating noise-like pulses of stochastic filling. Different spatiotemporal generation regimes varying by their stochasticity and periodicity properties are experimentally found. Further, we propose an experimental tool of ACF evolution mapping to reveal the constituents of thought-to-be stochastic radiation and will use this tool to directly detect various types of dark and bright localised structures, including spatio-temporal rogue waves and shock waves, generating within though-to-be stochastic temporal dynamics.

102

Amaury Mathis, Pierre-Ambroise Lacourt, Luc Froehly, Shanti Toenger, FEMTO-ST (France); Frédéric Dias, Univ. College Dublin (Ireland); Goery Genty, Tampere Univ. of Technology (Finland); John M. Dudley, FEMTO-ST (France)

Sergey V. Sergeyev, Chengbo Mou, Stanislav Kolpakov, Vladimir Kalashnikov, Sergei K. Turitsyn, Aston Univ. (United Kingdom) Rogue wave (RWs) as a concept has been initially introduced in oceanography to describe giant waves with amplitudes that are much larger than an average and so, despite low emergence probability, resulting in destructive impact in nature and society. The main obstacles in modelling and predicting RWs is in the scarcity of events and inability to perform fullscale experiments to cause rogue waves to appear in real-world scenarios such as financial markets, power grids, oceans, human brains etc. In this context, mode-locked lasers are perfect test bed systems to study RWs origin and techniques of mitigation with a potential to apply results in numerous disciplines – social sciences, natural sciences and technology and engineering. Here for the first time we demonstrate experimentally and theoretically a new mechanism of deterministic vector RWs emergence in erbium-doped fiber lasers mode-locked with carbon nanotubes. Unlike fast RW dynamics in lasers with pulse-to-pulse power variation, we have found slow vector rogue waves which have the states of polarization and power variations at the time scale of hundreds round trips. We showed that tuning the birefringence and anisotropy in cavity enables random switching between two orthogonal states of polarization that is similar to the stimulated by periodic barrier modulation transitions of the Brownian particle between two potential wells, i.e. Stochastic Resonance. Tailoring

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9732: Real-time Measurements, Rogue Events, and Emerging Applications anisotropy in the cavity leads to asymmetry in the escape probabilities from the potential wells that under certain conditions results in rare switching events with the output power distribution satisfying criteria of RWs.

9732-20, Session 4

Optical isolator based on topological insulator nano-particles Moti Fridman, Shir Shahal, Vlada Artel, Doron Naveh, BarIlan Univ. (Israel) Optical isolators which serve as one-way optical channels are a crucial component in numerous applications [1]. To obtain optical isolation, the time reversal symmetry must be broken. This braking of time reversal symmetry is usually done via Faraday rotator with constant magnetic field [2] and was also demonstrated with nonlinear interaction of traveling pump waves [3] and with circular polarized light manipulations [4]. We present, optical isolator based on the interaction between light and topological isolators. Our optical isolator is free from external magnetic field and is based on spontaneous time reversal symmetry braking by the topological insulators. The time reversal symmetry braking is obtained through the interaction of the traveling light in tapered fiber with the topological electrons in the surface and in the bulk of Sb2Te3 nano-particles. The interaction of light with the topological electrons rotates the input polarization similar to the Faraday rotator but with no external magnetic field. Our technique can lead to novel type of non-reciprocal fiber devices and can be implemented in on-chip photonic waveguides. The full experimental and theoretical details of our optical isolator will be presented. References: [1] D. Jalas, et. al. “What is – and what is not – an optical isolator” Nat. Photon. 7, 579 (2013) [2] K. Shiraishi, et. al., Appl. Opt. 23, 1103 (1984)

integrable turbulence. Numerical simulations of 1D-NLSE with stochastic initial conditions reproduce quantitatively the experiments. Our numerical investigations suggest that the statistical features experimentally observed rely on the stochastic generation of coherent analytic solutions of 1D-NLSE. Pierre Walczak, Stéphane Randoux, and Pierre Suret, Optical Rogue Waves in Integrable Turbulence, Phys. Rev. Lett. 114, 143903 (2015)

9732-22, Session 4

A route to rogue wave generation Saliya Coulibaly, Zheng Liu, Majid Taki, Univ. des Sciences et Technologies de Lille (France) The frequency combs have emerged as a powerful tool for high-resolution metrology. If in the beginning, ultrafast mode-locked lasers were the main sources of frequency combs, there are now new ways to generate them. By new ways, we especially refer to those based on the use of continuously pumped optical cavity containing a Kerr-type medium–Kerr frequency comb. That is, the Kerr frequency combs belong to the category of optical dissipative structures since they correspond to the spectra associated to the cavity solitons or the periodic solutions and so far, expected to exhibit complex dynamics. In this study, we focused on the dynamics of the periodic solutions that appear in Kerr cavities. More specifically, we study the route to the chaos that flows out from these structures. What we propose here is to consider the route to chaos by means of dynamical systems theory and chaos tools in extended systems. For this purpose, we consider the Lugiato-Lefever model which describes the dynamics of intra-cavity field in Kerr cavities. An instability of the basic solution of this model gives rise to a tunable periodic state with a comb-like spectrum. After providing an analytical description of this comb, its stability analysis have been carried out by means of computation the Lyapunov spectrum allowing to characterize the transition from stable comb to chaotic regime in which rogue waves have been observe and statistically characterized.

[3] H. Ramezani, et. al. Phys. Rev. A 82, 043803 (2010) [4] J. W. Goodman “Introduction to Fourier optics” (2005)

9732-23, Session 5

9732-21, Session 4

FDML lasers with MHz wavelength sweep repetition rates for fastest real-time OCT, spectroscopy, and sensing (Invited Paper)

Optical rogue waves in integrable turbulence Pierre Suret, Lab. de Physique des Lasers, Atomes et Molécules (France); Pierre Walczak, Stephane Randoux, Univ. des Sciences et Technologies de Lille (France) and Lab. de Physique des Lasers, Atomes et Molécules (France) We report optical experiments allowing to investigate integrable turbulence in the focusing regime of the one dimensional nonlinear Schrodinger equation (1D-NLSE). In analogy with broad spectrum excitation of onedimensional water-tank, we launch random initial waves in a single mode optical fiber. We have developed an original setup which allows the precise measurement of statistics of random light rapidly fluctuating with time. Inspired by the time-resolved fluorescence upconversion experiments and by the optical sampling (OS) oscilloscope, the principle of our method is based on asynchronous OS. Using our apparatus, we measure precisely the probability density function (PDF) of optical power of the partially coherent waves rapidly fluctuating with time. The typical time scale of the resolution is 250fs. In the experiments performed in the focusing regime, the PDF of optical power fluctuations is found to evolve from the normal law to a strong heavy-tailed distribution, thus revealing the formation of rogue waves in

Return to Contents

Wolfgang Draxinger, Wolfgang Wieser, Optores GmbH (Germany); Jan Philip Kolb, Tom Pfeiffer, Matthias Eibl, Univ. zu Lübeck (Germany); Thomas Klein, Optores GmbH (Germany); Sebastian N. Karpf, LMU München (Germany); Robert A. Huber, Univ. zu Lübeck (Germany) and LudwigMaximilians-Univ. München (Germany) Fourier Domain Mode Locked (FDML) lasers are narrowband, rapidly wavelength swept light sources that can generate more than 100nm sweep range at 1000-1550nm center wavelength. At linewidths of a few pm, several million wavelength sweeps per second are possible. The main application of FDML lasers is optical coherence tomography (OCT), where they can achieve about 10x higher speed compared to most other approaches. OCT is a recent microscopic 3D imaging technique and FDML enables imaging speeds of several ten volumes per second. The corresponding voxel rate of about 2 Gigavoxel/s can be sustained and recently live processing of the data on a consumer grade graphics processing unit was demonstrated. The live processing will be important for OCT applications like future OCT aided 4D surgical microscopes. Additionally, fast real-time OCT without live processing will have many more applications - especially in situations where patient motion, turbulent flow dynamics or a maximum total imaging time make non-realtime “sampling-type” approaches unacceptable. Besides the presentation of our own progress on evaluating emerging applications of ultra-high speed real-time OCT, the talk will review work and possibilities of FDML lasers for fast real-time spectroscopy and sensing applications.

+1 360 676 3290 · [email protected]

103

Conference 9732: Real-time Measurements, Rogue Events, and Emerging Applications

9732-24, Session 5

Single-shot high-resolution fiber-based phase-diversity photodetection of optical pulses Christophe Dorrer, Leon Waxer, Adam Kalb, Elizabeth Hill, Jake Bromage, Univ. of Rochester (United States) Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with highbandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources.1 Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of non-repetitive events. A temporal diagnostic based on phase diversity has been demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results.2 A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and algorithms are used to accurately reconstruct the input pulse shape from the measured instantaneous power of the ancillary pulses versus time and optical spectrum. This high-sensitivity (~30-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling, and with pulses significantly shorter than the photodetection impulse response. Experimental data obtained with various oscilloscopes having bandwidth in the 45- to 70GHz range will be presented to demonstrate accurate operation at pulse durations in the 1- to 100- ps range. Simulations of the diagnostic and pulsereconstruction algorithm will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DENA0001944, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article. 1. Walmsley, I. A. and Dorrer, C., “Characterization of ultrashort electromagnetic pulses,” Adv. Opt. Photon. 1, 308–437 (2009). 2. Dorrer, C., Waxer, L., Kalb, A., Hill, E. M. and Bromage, J., “Single-shot characterization of optical pulses below the resolution limit by phasediversified photodetection,” [Conference on Lasers and Electro-Optics 2015], OSA Technical Digest (online), Optical Society of America, Washington, DC, Paper JTh5C.5 (2015).

9732-25, Session 5

Spectral phase interrogation using nonlinear spectra (SPINS) Aram Gragossian, The Univ. of New Mexico (United States); Brook A. Jilek, Sandia National Labs. (United States); Mansoor Sheik-Bahae, The Univ. of New Mexico (United States) There are many techniques for calculating the spectral phase of ultrashort pulses. They all use multiple expensive components and are difficult to build and expensive to buy. We present and algorithm for short pulse characterization buy using one spectrometer and three spectra. Spectral Phase Interrogation using Nonlinear Spectra (SPINS) takes advantage of information embedded in fundamental, second harmonic (SH) and third harmonic (TH) spectra to retrieve the spectral phase and calculate pulse duration. SPINS generates trial SH and TH from the measured fundamental and an initial guess for the spectral phase. The spectral phase is approximated by 6th order Taylor expansion around central frequency. These coefficients are adjusted until the difference between measured and trial SH and TH is minimized. By comparing measured nonlinear spectra

104

with transform limited spectra we can determine suitable initial coefficients and the fastest optimization method [1-4]. The algorithm takes advantage of MATLAB built-in tools for constrained and non-constrained optimization. For complex synthetic pulses the algorithm converges in less than a minute with errors less than 0.1%. For measured pulses the error is limited by the uncertainty of nonlinear spectral measurements by different spectrometers which can be as large as 1%, therefore errors around or less than 1% for measured pulses are acceptable. Inclusion of third harmonic enables us to choose a better starting point and decreases the number of local minima which drastically reduces the convergence times and error. To eliminate time reversal ambiguity we can place a known material in the beam path and reduce the number of global minima to one.

9732-26, Session 5

Unstable multipulsing can be invisible to some ultrashort pulse measurement techniques Michelle Rhodes, Zhe Guang, Rick Trebino, Georgia Institute of Technology (United States) Multiple pulsing is a feature of most mode-locked ultrafast laser systems at very high pump powers, and slight variations in the pump power around certain regimes can cause sinusoidally-varying or even chaotic separations among pulses. While this behavior should be absent from well-engineered and well-aligned lasers, it is nevertheless still possible, especially if the system is poorly maintained. Although we have previously studied unstable trains of very noisy pulses, they are significantly different from simple satellite pulses. The impact of unstable multipulsing on modern pulse measurement methods is still unknown. While spectral shearing interferometry for direct electric field reconstruction (SPIDER) has been shown to be incapable of seeing fluctuating complex pulses, analytical models have suggested that small variations in separation between double-pulses could theoretically be visible in a SPIDER trace and in the resulting measured field, even if the relative phase of the two pulses is allowed to vary. However, we have now performed simulations and find that allowing only the relative phase of a satellite pulse to vary causes the satellite to wash out of the SPIDER measurement completely, even if the separation between pulses is stable. Allowing the separation between pulses (or other pulse parameters) to vary also does not improve matters: SPIDER continues to measure only a single pulse, a phenomenon known as the coherent artifact. On the other hand, although techniques like FROG and autocorrelation cannot accurately determine the precise properties of satellite pulses, they do succeed in seeing them.

9732-27, Session 5

Modelling of noise-like pulses generated in mode-locked fibre lasers Sergey Smirnov, Sergey M. Kobtsev, Novosibirsk State Univ. (Russian Federation) Noise-like pulses (NLP) generated in certain passively mode-locked regimes of fibre lasers [1] hold a substantial promise in various applications because they can carry relatively high energy, are not sensitive to the propagation medium dispersion, and can be non-linearly transformed with comparatively high efficiency [2, 3]. However, the structure of these pulses is still not completely understood, and neither is the statistics of temporal&spectral NLP components. The present paper for the first time proposes and studies a relatively simple NLP model that matches the experimental data well and suggests that there is a correlation between phases of neighbouring spectral components of NLP. Comparison of a relatively basic model of “random pulses” with the results of NLP modelling in mode-locked fibre lasers based on coupled non-linear Schrödinger equations (NLSE) demonstrates that

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9732: Real-time Measurements, Rogue Events, and Emerging Applications it is possible to use this proposed model for highly efficient simulations of promising NLP applications, such as material processing, non-linear frequency conversion, microscopy, and others. The present work explains the proposed NLP model and compares temporal distributions, intensity autocorrelation function of NLP, statistics of sub-pulse duration, and figures of mode cross-correlations predicted by new model and by NLSE. Further discussed is the possible application of the proposed model in studies of transitional lasing regimes (intermediate between generation of coherent pulses and NLP). 1. S. Smirnov, et al. Optics Express 20(24), 27447 (2012). 2. S. Smirnov, et al. Optics Express 22(1), 1058 (2014). 3. S. Kobtsev, et al. Optics Express 22(17), 20770 (2014).

9732-28, Session 5

Development of on-line laser power monitoring system Chien-Fang Ding, Meng-Shiou Lee, Kuan-Ming Li, National Taiwan Univ. (Taiwan) Since their invention, lasers have been applied in many fields, including material processing, communications, metrology biomedical engineering, and defense. Laser power is an important parameter in laser material processing, for example, laser cutting and laser drilling. Because laser power is influenced by ambient temperature, laser power status is monitored using laser power meters to ensure effective material processing. Current laser power meters have long response times. Consequently, they cannot measure laser power accurately within a short time. To achieve simultaneous laser power monitoring and effective material processing, we developed a complementary metal-oxide-semiconductor (CMOS) camera–based online laser power monitoring system. The CMOS camera captures images of an incident laser beam after it is split and attenuated by a beam splitter and a neutral density filter, respectively. By comparing the average brightness of the beam spots and the measurement results of the laser power meter, we can estimate laser power. In the continuous measurement mode, the average measurement error of the developed laser power monitoring system was approximately 3%, and it responded at least 3.6 s quicker than conventional thermopile power meters do. In the trigger measurement mode, which allows for synchronization of the CMOS camera with intermittent laser output, the average measurement error was lower than 3%, and the quickest response time was 20 ms.

Return to Contents

+1 360 676 3290 · [email protected]

105

Conference 9733: High-Power Diode Laser Technology and Applications XIV Monday - Tuesday 15–16 February 2016 Part of Proceedings of SPIE Vol. 9733 High-Power Diode Laser Technology and Applications XIV

9733-1, Session 1

Reliability of high power laser diodes with external optical feedback Dennis Bonsendorf, Stephan Schneider, Jens Meinschien, LIMO Lissotschenko Mikrooptik GmbH (Germany); Jens W Tomm, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany) Direct diode laser systems gain importance in the fields of material processing and solid-state laser pumping. With increased output power, also the influence of strong optical feedback has to be considered. Uncontrolled optical feedback is known for its spectral and power fluctuation effects, as well as potential emitter damage. We found that even intended feedback by use of volume Bragg gratings (VBG) for spectral stabilization may result in emitter lifetime reduction. To provide stable and reliable laser systems design, guidelines and maximum feedback ratings have to be found. We present a model to estimate the optical feedback power coupled back into the laser diode waveguide. It includes several origins of optical feedback and wide range of optical elements. The failure threshold of InGaAs and AlGaAs bars has been determined not only at standard operation mode but at various working points. The influence of several feedback levels to laser diode lifetime is investigated up to 4000h. The analysis of the semiconductor leads to a better understanding of the degradation process by defect spread. Facet microscopy, LBIC- and electroluminescence measurements deliver detailed information about semiconductor defects before and after aging tests. Laser diode protection systems can monitor optical feedback. With this improved understanding, the emergency shutdown threshold can be set low enough to ensure laser diode reliability and high enough to provide better machine usability avoiding false alarms.

9733-2, Session 1

Rapid stress-testing vs. long-term aging: a case study of 980-nm emitting singlespatial mode lasers Jens Wolfgang W. Tomm, Martin Hempel, Max-BornInstitut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); David Venables, Victor Rossin, Erik Zucker, Lumentum (United States); Thomas Elsaesser, Max-BornInstitut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany) Single-spatial mode lasers emitting at 980-nm are exposed to two types of lifetime testing, namely rapid stress-testing and long-term aging. We find that both activate the same sudden degradation mechanism, namely internal catastrophic optical damage at 0.6-1.0 mm behind the front facet. In the case of ultra-high power operation, we show that the mechanism that initializes this effect is a lateral widening of the optical mode, resulting in increased absorption outside the waveguide. Defects formed during longterm aging may eventually lead to a comparable mode distortion and finally to device failure. Single-pulse stress-testing allows for activation several degradation mechanisms in a device one after the other, and allows for distinguishing between gradual aging and defects that are independent of the aging status. Although the results presented are monitored with a rather complex setup, it turns out that monitoring the devices along their laser-axis with cameras provides rich information on gradual and sudden degradation effects. We expect that after once the acting mechanisms are understood, stress-tests

106

can be performed with simple and cheap setups, consisting of a pulse generator and a standard CCD-camera only. Although we are convinced that accelerated long-term aging tests will remain the main method for lifetime predictions of diode lasers, stress-tests could pave the way towards more time-efficient testing, e.g., for comparison of different technology variants in development. While this report focuses on the behavior of a specific device type, both setup and methodology are transferable to other types of diode lasers.

9733-3, Session 1

Reliability, failure modes, and degradation mechanisms in high power single- and multi-mode InGaAs-AlGaAs strained quantum well lasers Yongkun Sin, Nathan Presser, Zachary Lingley, Miles Brodie, Adam Bushmaker, Brendan Foran, Steven C. Moss, The Aerospace Corp. (United States) High-power single- and multi-mode InGaAs-AlGaAs strained QW lasers are critical components for telecommunications and potential space satellite communications systems. However, little has been reported on failure modes of state-of-the-art SM InGaAs-AlGaAs strained QW lasers although it is crucial to understand failure modes and underlying degradation mechanisms in developing these lasers that meet lifetime requirements for space satellite systems. Our present study addresses these issues by performing long-term life-tests followed by FMA and physics-of-failure investigation. We performed long-term accelerated life-tests on state-of-the-art SM and MM InGaAs-AlGaAs strained QW lasers. Our life-tests have accumulated over 20,000 test hours for SM lasers and over 35,000 test hours for MM lasers. FMA was performed on failed SM lasers using EBIC. This technique allowed us to identify failure types by observing dark line defects. All the SM failures we studied showed catastrophic and sudden degradation and all of these failures were bulk failures. Our group previously reported that bulk failure or COBD is the dominant failure mode of MM InGaAs-AlGaAs strained QW lasers and this is the first report demonstrating that the dominant failure mode of SM and MM InGaAs-AlGaAs strained QW lasers is the bulk failure. Since degradation mechanisms responsible for COBD are still not well understood, we also employed FIB and high-resolution TEM to further study dark line defects and dislocations in pre- and post-aged SM and MM lasers. In addition, the photocurrent spectra were measured from localized areas to study the effects of COBD on changes in absorption characteristics in MM lasers.

9733-4, Session 1

Reliability study on high power 638-nm triple emitter broad area laser diode Tetsuya Yagi, Kyosuke Kuramoto, Kaoru Kadoiwa, Ryuta Wakamatsu, Motoharu Miyashita, Mitsubishi Electric Corp. (Japan) The digital cinema projector based on laser light source started its installation to the theaters, and the laser diode (LD) backlight LCD already appeared in the consumer market. So far, the next may be a laser based projector with one spatial light modulator (SLM), which uses the laser light source under the pulse condition for time division color expression. We already developed the 638 nm triple emitter broad area (BA) LD assembled

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9733: High-Power Diode Laser Technology and Applications XIV on 9.0-mm TO package for this application, which outputs peak power of 5.5 W under pulse operation with duty cycle (Dc) of 30%, 25 C. In this paper, the latest reliability study on this LD will be described in detail. Main cause of the degradation of 638-nm BA-LD is catastrophic optical mirror degradation (COMD). It was reported that the output power, at which the COMD occurs, (Pcod) decreases as the aging time goes by. When Pcod reaches to the operation power, the failure due to COMD occurs. The Pcod behaviors on the several aging conditions were studied. It was revealed that the mean time to failure (MTTF) of the LD was proportional to the -4.3 power of the output power. The long term aging under the over-drive condition was also performed. The emitter failed individually and the failed emitter didn’t affect the other emitters in the same chip. By using them, the MTTF of this LD was estimated exceeding 20,000 hours under the output of 2.5 W, Dc of 30%.

9733-5, Session 1

Sequential description of the catastrophic optical damage of high power laser diodes Jorge Souto, Jose Luis Pura, Alfredo Torres, Juan Jimenéz, Univ. de Valladolid (Spain); Mauro A. Bettiati, Francois J. Laruelle, 3SP Technologies S.A.S. (France) The catastrophic optical degradation (COD) of high power laser diodes is described on the bases of the cathodoluminescence (CL) analysis of the degraded areas, and a thermomechanical model accounting for the mechanism leading the degradation process. The COD is frequently observed at the front mirror; although, under very high power conditions (pulsed current operation) internal COD can also occur. CL is a very suitable experimental technique to reveal the main features of degradation in laser diodes; the defects generated by the degradation in the laser cavity are observed by CL imaging; simultaneously spectrally resolved CL permits to monitor the spectral changes induced by the degradation. The COD is observed as a very local process, associated with the formation of networks of extended defects and subsequent propagation as a result of the local enhancement of the temperature. In view of this observation, one can set-up a thermomechanical model describing the thermal runaway leading to the COD. The thermal stresses generated by the local heating are the leading forces driving the plastic deformation of the laser structure; the generation and propagation of networks of dislocations, mostly localized in the QW layer, are observed in the CL images. Important physical parameters of the laser structure involved in this process are the thermal conductivity and the mechanical strength. We demonstrate that the evolution of these parameters during laser operation accounts for the sudden temperature increase in local regions of the laser cavity.

9733-6, Session 1

Improved long wavelength 14xx and 19xx nm InGaAsp/InP lasers Tawee Tanbun-Ek, Rajiv Pathak, Zuntu Xu, Heiko Winhold, Serguei Kim, Fei Zhou, Arne-Heike Meissner-Schenk, Michael Peter, Geunmin Ryu, David A. Schleuning, Coherent, Inc. (United States) We report on our progress developing long wavelength high power laser diodes based on the InGaAsP/InP alloy system emitting in the range from 1400 to 2010 nm. Output power levels exceeding 50 Watts CW and 40% conversion efficiency were obtained at 1470 nm wavelength from 20% fill factor (FF) bars with 2 mm cavity length mounted on water cooled plates. Using these stackable plates we built a water cooled stack with 8 bars, successfully demonstrating 400 W at 1470 nm with good reliability. In all cases the maximum conversion efficiency was greater than 40% and the maximum power achievable was limited by thermal rollover. For lasers emitting in the range from 1930 to 2010 nm we achieved output power

Return to Contents

levels over 15 W and 20 % conversion efficiency from 20% FF bars with 2 mm cavity length on a conductively cooled platform. Life testing of the 1470 nm lasers bars over 14,000 hours under constant current mode has shown no significant degradation.

9733-7, Session 2

A fiber-coupled 9xx module with tap water cooling David A. Schleuning, Athanasios N. Chryssis, Geunmin Ryu, Guoli Liu, Heiko Winhold, Li Fan, Zuntu Xu, Tawee TanbunEk, Sami Lehkonen, Bruno Acklin, Coherent, Inc. (United States) Many direct diode and fiber laser pumping applications require a multi-kW laser diode module. A new 9xx nm laser diode chip has been developed with improved efficiency, brightness, and reliability. A water-cooled packaging architecture utilizing hard solder has been developed using an electrically isolated cooler which provides low thermal resistance ( 95% power into 0.15NA). The goal of the present study is to reduce pump count by increasing the diode power level, while maintaining a similar brightness level of the ST pump. In this way, we can reduce the total pump cost (in terms of $/W) at the system level. Laser diodes are spatially multiplexed into a 135um diameter core fiber. The package architecture leverages the same optical train and mechanical structure that was qualified previously. As compared to ST form factor, the package is extended by < 1”, whereas the height, width and bolt pattern remain unchanged for backward compatibility. With the latest-generation laser diode pump platform, we have achieved 250W CW power at 22A at ~ 30C case temperature. The power conversion efficiency is 55% (peak) that drops to 47% at 22A with little thermal roll over. Greater than 95% of the light is collected at < 0.15NA at 16A drive current.

As applications for diode lasers in the fields of solid-state pumping, fiber laser pumping, and materials processing continue to demand higher power and brightness, there is a strong market for highly efficient, lightweight diode pump modules. Many of these applications, such as airborne or field transportable systems, require a high degree of mobility, while others may simply benefit from lower module size where space is at a premium. We present an update on several lightweight diode pump modules with power output in the range of 600W to almost 1kW, weight-to-power ratio (WPR) from 0.9 to 0.7 kg/kW, and electro-optical efficiencies well in excess of 50%. DILAS has previously reported on the IS46, a successful pumping product with a 300W output from a ~300g module and many hundred modules in the field. Here we present an updated version of the IS46 providing ~350W output power at the same weight. Also presented are updated results from the previously reported IS53 module, which now shows 600W of output, and data from a new prototype capable of producing nearly 1kW from a 225um, 0.22NA fiber. The basic technologies that allow such compact systems will be discussed, with special emphasis on the engineering challenges of high efficiency, lightweight system design. In particular, primary drivers that allow high optical efficiency, the management of waste heat, and the design of the associated laser cooling architecture will be reviewed.

9733-12, Session 3

Reduced-mode (REM) diodes enable high brightness fiber-coupled modules Manoj Kanskar, Ling Bao, Zhigang Chen, David Dawson, Mark DeVito, Weimin Dong, Mike P. Grimshaw, Xinguo Guan, Marty Hemenway, Keith Kennedy, Rob Martinsen, Wolfram Urbanek, Shiguo Zhang, nLIGHT Corp. (United States) There is an increasing demand for high-power, high-brightness diode lasers at 885 nm, 915 nm and 976 nm for applications such as fiber laser pumping, materials processing, solid-state laser pumping, and consumer electronics manufacturing. The kilowatt CW fiber laser pumping (915 nm for industrial fiber lasers & 976 nm for directed energy fiber amplifiers) particularly requires the diode lasers to have both high power and high brightness in order to achieve high-performance. This paper presents our continued progress in the development of high power and high brightness fiber-coupled product platform, element, to address these applications. Recent improvements in fiber-coupled power has been enabled by significant advances in the slow-axis brightness of broad area lasers. We have demonstrated slow-axis brightness as high as 4.3 W/mm-mrd resulting from reducing the number of allowed modes in the slow-axis direction. Further improvement is underway. This new generation of reduced-mode diodes (REM-diodes) have half the slow-axis divergence compared to regular BALs at the same operating powers. As a result, we have achieved >160 watts from a 2?6 element module in the 9xx nm spectral range out of a 105 µm/0.15 NA beam. We have also extended the REM concept to geometrically multiplexing multiple of these devices to scale up power at higher BPP. We will present performance and reliability data on these devices. Further slow-axis brilliance improvement is underway and we will report the latest findings.

9733-13, Session 3

9733-11, Session 3

DPAL pump system exceeding 3kW at 766nm and 30 GHz bandwidth

Lightweight diode laser pump modules push to a new class of higher power and lower weight

Tobias P. Koenning, Dan McCormick, David A. Irwin, Dean Stapleton, Tina Guiney, Steve G. Patterson, DILAS Diode Laser, Inc. (United States)

David A. Irwin, DILAS Diode Laser, Inc. (United States)

108

Due to their low quantum defect, diode pumped alkali metal vapor lasers (DPALs) offer the promise of scalability to very high average power

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9733: High-Power Diode Laser Technology and Applications XIV levels while maintaining excellent beam quality. Research on DPALs has progressed to ever increasing power levels across multiple gain media species over the last years, necessitating pump power in the kW range. Each material requires a specific pump wavelength: near 852 nm for cesium, 780 nm for rubidium, 766 nm for potassium, and 670 nm for lithium atoms. The shorter pump wavelength below 800nm are outside the typical wavelength range for pump diodes developed for diode pumped solid state lasers (DPSS). The biggest challenge in pumping these materials efficiently is the need for maintaining the narrow gain media absorption band of approximately 0.01 nm while greatly increasing power. Typical high power diode lasers achieve spectral widths around 3nm (FWHM) in the near infrared spectrum, but optical gratings may be used internal or external to the cavity to reduce the spectral width. Recently, experimental results have shown yet narrower line widths ranging from picometers at very low power levels to sub-100 picometers for water cooled stacks around 1kW of output power. The focus of this work is the development of a fiber-based pump system for potassium DPAL. The individual tasks are the development of high power 766nm chip material, a fiber-coupled module as a building block, and a scalable system design to address power requirements from hundreds of watts to tens of kilowatts. Results for a 3kW system achieving ~30GHz bandwidth at 766nm will be shown. Approaches for power-scaling and size reduction will be discussed.

9733-14, Session 4

Spectral beam combining of multi-single emitters Baohua Wang, Weirong Guo, Zhijie Guo, Dan Xu, Jing Zhu, Qiang Zhang, Thomas C. Yang, Xiaohua Chen, BWT Beijing Ltd. (China) Spectral beam combination expands the output power while keeps the beam quality of the combined beam almost the same as that of a single emitter. Spectral beam combination has been successfully achieved for high power fiber lasers, diode laser arrays and diode laser stacks. We have recently achieved the spectral beam combination of multiple single emitter diode lasers. Spatial beam combination and beam transformation are employed before beams from 25 single emitter diode lasers can be spectrally combined. An average output power about 220W, a spectral bandwidth less than 9 nm (95% energy), a beam quality similar to that of a single emitter and electro-optical conversion efficiency over 46% are achieved. In this paper, Rigorous Coupled Wave analysis is used to numerically evaluate the influence of emitter width, emitter pitch and focal length of transformation lens on diffraction efficiency of the grating and spectral bandwidth. To assess the chance of catastrophic optical mirror damage (COMD), the optical power in the internal cavity of a free running emitter and the optical power in the grating external cavity of a wavelength locked emitter are theoretically analyzed. Advantages and disadvantages of spectral beam combination are concluded.

We present our building block system concept, which consists of 500 W building blocks, which will be stacked via variations of combining methods to multi kW systems, while enabled easy field maintenance. The key subassembly is a structure consisting of single emitters, automatically aligned individual fast axis collimation lenses and a monolithic slow axis collimation and redirection device. By varying the diode wavelengths they can later be combined by various techniques and therefore power scaled. The diodes on a subassembly are vertically stacked, can be wavelength stabilized and lead to an output power of well above 100 W with BPP of 500 W optical output power within a 100µm fiber with 0.15 NA or by combination of several building blocks up to multi kW systems without change in beam quality. In addition the built-in electronics is monitoring, controlling and diagnosing each individual wavelength channel via, further more due to the 48 V architecture and only 12 A per channel, the laser systems are capable of short µs pulses up to cw. The combination of this intelligent electronics with industrial interfaces as TCP/IP, which allows remote control and –diagnostic, and the building block concept enables easy and sustainable field maintenance.

9733-16, Session 4

Compact 35µm fiber coupled diode laser module based on dense wavelength division multiplexing of NBA mini-bars Ulrich Witte, Martin Traub, Angelo Di Meo, David Rubel, Marcus Hamann, Stefan Hengesbach, Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany) We present a compact, modular and cross talk free approach for dense wavelength division multiplexing of high power diode lasers based on ultrasteep dielectric filters. The filters are characterized in a newly developed characterization stage and have a band edge steepness of approximately 0.7 nm. One submodule consists of two mini bars that are geometrically stacked in the fast axis (FA). The collimated beams of the individual emitters are subsequently spectrally combined by use of dielectric filters. For fiber coupling, a rotationally symmetric focusing lens is utilized. The mini bars consist of 5 narrow stripe broad area (NBA) emitters with a beam parameter product in the range of 2 mm mrad and a wavelength spacing of 2.5 nm between 2 adjacent emitters. The near field with of the emitters is 30 µm up to 40 µm. Internally stabilized DFB-NBA laser diodes are compared with AR-coated and externally stabilized NBA laser diodes. For external stabilization one partially reflective mirror is used to build an external selflocking cavity. Experimental results for fiber coupling (35 µm core diameter, NA < 0.18) of internally and externally stabilized diode lasers are presented. Additionally, optical losses are analyzed and alternative optical designs to overcome the current limitations of the setup are discussed.

9733-17, Session 4

9733-15, Session 4

Building block diode laser concept for high brightness laser output in the kW range and its applications Andreas Grohe, Fabio Ferrario, Haro Fritsche, Thomas Hagen, Holger Kern, Ralf Koch, Bastian Kruschke, Axel Reich, Dennis Sanftleben, Ronny Steger, Till Wallendorf, Wolfgang Gries, DirectPhotonics Industries GmbH

Return to Contents

(Germany)

High-power operation of coherently coupled tapered laser diodes in an external cavity Guillaume Schimmel, Ioana Doyen, Sylvie Janicot, Marc Hanna, Patrick Georges, Gaëlle Lucas-Leclin, Lab. Charles Fabry (France); Jonathan Decker, Paul Crump, Goetz Erbert, Ferdinand-Braun-Institut (Germany); Simeon Kaunga-Nyirenda, Daniel Moss, Steve Bull, Eric Larkins,

+1 360 676 3290 · [email protected]

109

Conference 9733: High-Power Diode Laser Technology and Applications XIV The Univ. of Nottingham (United Kingdom)

9733-19, Session 4

Coherent Beam Combining (CBC) consists in superposing several beams that are coherent with each other, thereby generating a single high-power laser beam with excellent spectral and spatial properties. We investigate a new CBC architecture using a common laser external cavity on the back side of the emitters for phase locking, while coherent beam superposition of phase-locked beams is realized on the front side. This technique leads to a separation of the phase-locking stage – which takes place in the common external cavity on the rear side of the lasers - and the beam combining stage – which is achieved on the front side outside the cavity. In this contribution, this technique is applied to high-brightness tapered devices demonstrating the potential of extended-cavity phase-locking arrangements for high-power operation.

Simultaneous frequency stabilization and high-power dense wavelength division multiplexing (HP-DWDM) using an external cavity based on volume Bragg gratings (VBGs)

The rear-side common resonator used for phase-locking of the two emitters is a passive external cavity designed as a Michelson interferometer. The phase-locking range and the resistance of the external cavity to perturbations are investigated. On the front side the combining efficiency is above 80% and results in an output power of 6.5 W in a nearly diffractionlimited beam (M?(4?) ≤ 1.2). The corresponding electrical-to-optical efficiency is above 20%. The combined power is stabilized with an automatic adjustment of the driving currents.

Multiplexing technologies enable the development of high-brightness diode lasers for direct industrial applications. We present a compact High-Power Dense Wavelength Division Multiplexer (HP-DWDM) with an average channel spacing of 1.7 (1.5) nm and a subsequent external cavity mirror to provide feedback for frequency stabilization and multiplexing in one step. The „self-locking“ multiplexing unit consists of four Volume Bragg Gratings (VBGs) with 99% diffraction efficiency and seven dielectric mirrors to overlay the radiation of five input channels with an adjustable channel spacing of 1-2 nm. In detail, we focus on the analysis of the overall optical efficiency and the change of the beam parameter product and the spectral width. The performance is demonstrated using five 100 microns wide multimode 9xx single emitters with M2 ≤ 17. Because of the feedback the lateral (multimodal) spacial and angular intensity distribution changes strongly and the beam parameter product decreases by a factor of 1.2 to 1.9. Thereby the angular intensity distribution is more affected than the near field intensity distribution. The spectral width per emitter decreases to 3-200 pm (FWHM) depending on the injection current and the reflectance of the feedback mirror (0.75%, 1%, 2%, 4% or 6%). Thus, the laser bandwidth is much smaller than the wavelength selectivity of the Volume Bragg Grating due to gain narrowing and an optimized feedback strength. The overall optical multiplexing efficiency ranges between 77% and 86%. With some modifications (e.g. enhanced AR coatings) we expect 90-95%.

9733-18, Session 4

Wavelength locking of single emitters and multi-emitter modules: Simulation and experiments Dan Yanson, Noam Rappaport, Ophir Peleg, Yuri Berk, Nir Dahan, Genady Klumel, Ilya Baskin, Moshe Levy, Yoram Karni, SCD SemiConductor Devices (Israel) Wavelength-stabilized high-brightness single emitters are commonly used in fiber-coupled laser diode modules for pumping Yb-doped lasers at 976 nm, and Nd-doped ones at 808 nm. We investigate the spectral behavior of single emitters under wavelength-selective feedback from a volume Bragg (or volume hologram) grating (VBG) in a multi-emitter module. By integrating a full VBG model as a multi-layer thin film structure with commercial raytracing software, we simulated wavelength locking conditions as a function of beam divergence and angular alignment tolerances. Good correlation between the simulated VBG feedback strength and experimentally measured locking ranges, in both angle and laser temperature, is demonstrated. The challenges of assembling multi-emitter modules based on beamstacked optical architectures are specifically addressed, where a common VBG is placed to wavelength-lock all emitters together. The wavelength locking conditions must be achieved simultaneously with a high fiber coupling efficiency for each emitter in the module. It is shown that even a minor angular misorientation between fast and slow-axis collimating optics can have a dramatic effect on the spectral and power performance of the module. We report on the progress towards development of a wavelength-stabilized fiber laser pump module, which uses a VBG to provide wavelength-selective optical feedback in the collimated portion of the beam. Powered by our purpose-developed high-brightness single emitters, the module reaches 45 W output from a 105 µm core, 0.15 NA fiber with an 0.3 nm linewidth at a wavelength of 976 nm. Preliminary wavelength-locking experiments at 808 nm are also presented.

110

Stefan Hengesbach, Sarah Klein, Carlo Holly, Ulrich Witte, Martin Traub, Hans-Dieter Hoffmann, Fraunhofer-Institut für Lasertechnik (Germany)

9733-20, Session 5

940nm QCW diode laser bars with 70% efficiency at 1 kW output power at 203K: analysis of remaining limits and path to higher efficiency and power at 200K and 300K (Invited Paper) Carlo F. Frevert, Frank Bugge, Steffen Knigge, Arnim Ginolas, Götz Erbert, Paul Crump, Ferdinand-Braun-Institut (Germany) Both high-energy-class laser facilities and commercial high-energy pulsed laser sources require reliable optical pumps with the highest pulse power and electro-optical efficiency. Although commercial quasi-continuouswave (QCW) diode laser bars reach output powers of 300…500W further improvements are urgently sought to lower the cost per Watt, improve system performance and reduce overall system complexity. Diode laser bars operating at temperatures of around 200K show significant advances in performance, and are particularly attractive in systems that use cryogenically cooled solid state lasers. We present the latest results on 940nm, passively cooled, 4mm long QCW diode bars which operate under pulse conditions of 200?s, 10Hz at an output power of 1kW with efficiency of 70% at 203K: a two-fold increase in power compared to 300K, without compromising efficiency. We discuss how custom low-temperature design of the vertical layers can mitigate the limiting factors such as series resistance while sustaining high power levels. We then focus on the remaining obstacles to higher efficiency and power, and use a detailed study of multiple vertical structures to demonstrate that the properties of the active region are a major performance limit. Specifically, one key limit to series resistance is transport in the layers around the active region (resistance is a

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9733: High-Power Diode Laser Technology and Applications XIV clear function of well depth) and the differential internal efficiency is closely correlated to the transparency current density. Tailoring the barriers around the active region and reducing transparency current density thus promise bars with increased performance at temperatures of 200K as well as 300K.

9733-21, Session 5

High duty-cycle, high-efficiency QCW stacks for medical applications Alex Kindsvater, Matthias Schroeder, Ekkehard A. Werner, Sebastian Seidel, Martin Woelz, Valentin Loyo, JENOPTIK Laser GmbH (Germany) High duty-cycle, high-efficiency QCW stacks are ideally suited for medical and cosmetic applications. The 8-bar stack with a bar-to-bar pitch of 1,7mm emits 808 or 940nm wavelength with 65 to 95 Joule depending on pulse conditions at 25°C water temperature. The value is limited by thermal effects and can be increased by choosing the lower limit of the cooling specification. This stack is specified for up to 130 A at 50ms, 15% d.c., down to 45 A at 400ms, 55% d.c. The reliability for long pulse operation is targeted to reach up to 450 hours of total life time. That is equivalent to 15 Mshots at pulse durations less or equal 100ms or 4 Mshots at 400ms. The stack heat sink is cooled by filtered tap water at 15 – 25°C with flow rates of up to 0.9 ±0.1 l/min at inlet pressures up to 1.7 ±0.1 bar. Efficiency, thermal impedance and wavelength plots are presented in the paper.

9733-22, Session 5

980nm semiconductor lasers and spot size converter monolithically integrated technology research Wentao Guo, Manqing Tan, Institute of Semiconductors (China) The 980nm semiconductor lasers are the important pump sources of the Erbium-Doped Fiber Amplifier (EDFA) and Erbium-Doped Superfluorescent Fiber Source (ED-SFS). They have important significance to the high speed, large capacity, long distance all-optical communication systems and the high-precision fiber optic gyroscope (FOG). The asymmetric twin waveguide (ATG) technology was used to prepare the 980nm FP cavity semiconductor lasers and the spot size converter integrated devices. The SSC-LD equivalent resonator model has been established to do the theoretical calculation of the coupling coefficient and gain coefficient. The design of the device structure has been optimized by researching the influencing mechanism of tapered waveguide’s shape and the epitaxial layer’s structure parameters on the output characteristics of the devices. The technical scheme of SSC-LD’s preparation has been studied on using ATG technology. Finally, the sample with the center wavelength of 980nm±3nm, less than 10° for vertical farfield divergence angle has been made in the experiment.

9733-23, Session 5

Assessing the influence of the vertical design on the lateral beam quality of highpower broad area diode lasers Martin Winterfeldt, Steffen Knigge, André Maaßdorf, Ferdinand-Braun-Institut (Germany); Martin Hempel, Jens W. Tomm, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany); Götz Erbert, Paul Crump, Ferdinand-Braun-Institut (Germany) GaAs-based high-power broad-area diode lasers deliver NIR optical

Return to Contents

output powers Popt > 10W with efficiency > 60%. However, their application is limited due to poor in-plane beam parameter product BPPlat=0.25?FF95%?w95% (FF95% and w95% are emission angle and aperture, 95% power content). We present progress in improving BPPlat by choosing the proper vertical designs. First, we show that large vertical asymmetry is beneficial, with extreme-double-asymmetric (EDAS) waveguide designs delivering a ~1 mm?mrad reduction in the BPP ground level, compared to a reference (more symmetric) design. Possible reasons include a reduced number of lateral modes, a modified thermal lens profile or an improvement in the beam quality of the individual modes. Measured thermal profiles show no clear evidence for a difference in the lateral thermal lens when EDAS designs are used and 2-D waveguide simulation based on the profiles shows no significant difference in confinement factor of higher order modes. Therefore, the improved BPPlat is most likely due to an improvement in the lateral mode quality. Second, we test the benefit of low modal gain factor Gg0, predicted to improve BPPlat via a suppression of filamentation. EDAS-based lasers with single and double quantum well active regions were compared, with 2.5x reduced Gg0, for 2.2x reduced filament gain. However, no difference is seen in measured BPPlat, giving evidence that filamentary processes are no longer a limit. In contrast, devices with lower Gg0 demonstrate an up to twofold reduced near field modulation depth, potentially enabling higher facet loads and increased device facet reliability.

9733-24, Session 5

Optical mode engineering and high power density per facet length (>8.4 kW/cm) in tilted wave laser diodes Nikolay Ledentsov, Vitaly A. Shchukin, VI Systems GmbH (Germany); Mikhail V. Maximov, Nikita Y. Gordeev, Nikolay A. Kaluzhniy, Sergey A. Mintairov, Alexey S. Payusov, Yuri M. Shernyakov, Ioffe Physical-Technical Institute (Russian Federation) Thick waveguide laser diodes allow a reduced impact of the catastrophic optical mirror damage and thermal “smile” effects in laser chips and bars. Tilted Wave Lasers (TWLs) [1] based on optically coupled thin active and thick passive waveguides may offer an ultimate solution, in which the thickness of the passive waveguide can vary from ~10–35 um realized by an epitaxial layer [2] and up to ~100–150 um [2] if a transparent substrate is employed as the passive waveguide. Two vertical lobe emission has an advantage for the application in coherent laser stacks, based on external glass plate reflector. We show that by proper engineering of the waveguide one can realize high performance TWL diodes at different tilt angles of the lobes (e.g., +/–27 degrees or +/–9 degrees) to the junction plane. The TWL with the lobes at +/–9 degrees allows above 95% of the power to be emitted within a vertical angle below 25 degrees, which is important for laser stack applications also using conventional optical coupling schemes. A single lobe emission at zero angle can be realized. A high differential efficiency ~90% and a current–source limited pulsed power >42W for as–cleaved TWL device at a cavity length of 1.5 mm and a stripe width of 50 um is shown. Thus the power per facet length in a laser bar in excess of 8.4 kW/cm can be reached. The work was supported by ZIM Program of BMWi (Project COLIBRI). [1] N. N. Ledentsov, et al., Electron. Lett. 47, 1339–1340 (2011) [2] N. N. Ledentsov, et al., Proc. SPIE 8965, 89650Q (2014)

9733-25, Session 5

Single-mode tapered DBR lasers emitting 400 mW at 1550 nm Jukka Viheriälä, Joel Salmi, Tampere Univ. of Technology (Finland); Jaakko M. Mäkelä, Univ. of Turku (Finland);

+1 360 676 3290 · [email protected]

111

Conference 9733: High-Power Diode Laser Technology and Applications XIV Antti T. Aho, Heikki A. Virtanen, Tomi Leinonen, Mihail M. Dumitrescu, Mircea Guina, Tampere Univ. of Technology (Finland) We report the development and the performance of 1550 nm tapered DBR laser diodes. These devices are particularly attractive for applications requiring eye-safe high power single-mode operation, such as LIDAR and range-finding. The DBR was fabricated using a regrowth-free process based on surface gratings and InP/AlGaInAs QWs. A CW output power as high as 400 mW in single-mode operation was achieved at room-temperature. At maximum output power the SMSR was 45 dB, proving the excellent behavior of the surface gratings. The ridge waveguide and DBR surface grating were defined using soft-UVNIL, while the patterning of metals and dielectrics was done using regular UV-lithography. This “mix-and-match” processing technique combines the best from both lithography methods. To our knowledge this is the first demonstration of DBR lasers fabricated using soft-UV-NIL on wafer-scale. The processed chips consisted of a 1 mm long DBR-grating section, a 1 mm long straight ridge waveguide section and a tapered section with 6 degrees full opening angle. The length of the tapered section has been varied between 0.5 mm and 1.85 mm to study the power scalability. For characterization the chips were p-side-down mounted on an AlN170submount containing multiple electrically isolated AuSn-pads, which enabled driving each laser section separately. By increasing the length of tapered section from 0.5 mm to 1.85 mm the maximum CW power at room temperature could be scaled from 125 mW to 400 mW. The design guidelines and power scaling capabilities will be discussed.

9733-26, Session 6

High-power single emitters and low fill factor bars emitting at 808 nm Agnieszka Pietrzak, Ralf Hülsewede, Martin Zorn, JENOPTIK Diode Lab GmbH (Germany); Jens Meusel, JENOPTIK Laser GmbH (Germany); Jürgen Sebastian, JENOPTIK Diode Lab GmbH (Germany) Single emitters emitting at a wavelength around 808 nm are highlydesired as pump sources of low power solid state lasers which are widely utilized e.g., in micro-marking, metrology-instrumentation, and for build compact NIR-light sources. For this wavelength region different quantumwell material can be used resulting in different polarization directions. We present the latest development of high-power single emitters having emitter apertures of 95 µm, 100 µm and 200 µm based on TM-polarized material. Furthermore, different cavity length of 2 mm and 4 mm are investigated. Short-cavity devices were characterized up to powers over 4 W with a wall plug efficiency above 60%. Long-cavity devices were characterized up to their maximum optical output power of 15 W from 100 µm wide emitters and 22 W from 200 µm wide emitters with 4 mm cavity length mounted on passively cooled heat-sinks. The operation point of these devices is 8 W and 12 W, respectively with wall-plug efficiencies of ~55%. Furthermore first results on 5-emitters bars are presented operating at 40 W.

9733-27, Session 6

Thermal investigation on high power dfb broad area lasers at 975 nm, with 60% efficiency Roberto Mostallino, Michel Garcia, III-V Lab. (France); Yannick Deshayes, Univ. Bordeaux 1 (France); Alexandre Larrue, Yannick Robert, Eric Vinet, III-V Lab. (France); Laurent Bechou, Univ. Bordeaux 1 (France); Michel

112

Lecomte, Olivier Parillaud, Michel Krakowski, III-V Lab. (France) The request of high power diode lasers in the range of 910-980nm is growing. This kind of device has many applications, such as fiber laser pumping, material processing, solid-state laser pumping, defense and medical/dental applications. The key role of this device lies in the wall plug efficiency (?e ) of converting electrical power into optical power. The high value of ?e allows high power level and reduces the level of current heating in lasers. The need of wavelength thermal stabilization is more evident in the case of multimode 975nm diode lasers used for pumping the Yb, Er and Yb/Er co-doped solid-state laser, which has a narrow absorption line close to 975nm. Narrow spectral width operation (45dB with a width >20k hrs reliability for products including 60W 18% fill factor and 80W 28% fill factor conduction cooled bars.

9733-29, Session 6

Characterization of high performance silicon-based VMJ PV cells for laser power transmission applications Mico Perales, MH GoPower Co., Ltd. (United States); Meihuan Yang, John Wu, Talan Hsu, MH GoPower Co., Ltd. (Taiwan); Wei-sheng Chao, MH GoPower Co., Ltd. (Taiwan) and MH GoPower Co., Ltd. (Taiwan); Kun-hsien Chen, MH GoPower Co., Ltd. (Taiwan) and MH GoPower Co., Ltd (Taiwan); Terry Zahuranec, MH GoPower Co., Ltd. (United States) Continuing improvements in the cost and power of laser diodes have been critical in launching the emerging fields of power over fiber (PoF), and laser power beaming. Laser power is transmitted either over fiber (for PoF), or through free space (power beaming), and is converted to electricity by photovoltaic cells designed to efficiently convert the laser light. MH

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9733: High-Power Diode Laser Technology and Applications XIV GoPower’s (MHGP) VMJ PV cell, designed for high intensity photovoltaic applications, is fueling the emergence of this market, by enabling unparalleled photovoltaic receiver flexibility in voltage, cell size, and power output. Our research examines the use of the VMJ cell in these laser power transmission applications. We first fully characterize the performance of the VMJ cell under various laser conditions, including multiple near IR wavelengths, multiple light intensities ranging from mW to tens of watts per cm2, and different beam uniformities. We also investigate the impact of the physical dimensions (length, width, and height) of the VMJ cell on its performance. We then delve deeper into VMJ cell performance within the power over fiber application, as we examine the effectiveness of the VMJ cell in various receiver packages that deliver target voltage, uniformity, intensity, and power levels. By designing and characterizing multiple receivers, we illustrate techniques for packaging the VMJ cell for achieving optimal performance and target voltages, as well as minimizing package size, for power over fiber applications.

9733-30, Session 7

Integrated high power VCSEL systems Holger Moench, Ralf Conrads, Stephan Gronenborn, Philips Technologie GmbH (Germany); Xi Gu, Philips Lighting B.V. (Netherlands); Michael Miller, Philips GmbH U-L-M Photonics (Germany); Pavel Pekarski, Jens PollmannRetsch, Philips Research (Germany); Armand Pruijmboom, Philips Lighting B.V. (Netherlands); Ulrich Weichmann, Philips Technologie GmbH (Germany)

Fraunhofer-Institut für Produktionstechnologie IPT (Germany) In this paper we present an industrial grade assembly solution for micro optics utilized in high power diode laser stacks. With ever-rising demand for HPDL-stacks higher degrees of automation are becoming economically viable solutions. Proven assembly technology and concepts can be transferred from close industrial domains as a starting point but need to be extended for a successful application in laser industry. Quality demands of micro optics in high-power environments cannot be satisfied with geometric specification alone; hence alignment tasks of optical components often focus on the optimization of product functions instead. The integration of these domain specific active alignment algorithms and measurement setups in classic industrial automation environments are main challenges when moving towards highly automated solutions. Stack assembly is additionally demanding as measurement equipment and current stack level need to be synchronized during the assembly. Furthermore laser bars are individually contacted to reduce heat progression and excessive laser radiation. We will present a detailed analysis of integration challenges and viable approaches in regard to software, compact measurement equipment for active alignment and unbroken process observation for optimized shrinkage compensation based on calculated quality metrics. Furthermore we analyze the process capability and cycle times of an automated FAC assembly for stacks.

9733-32, Session PTue

High power VCSEL system technology extends to proper coolers, bonding technology and integrated optics i.e. far beyond the VCSEL chip itself. The paper discusses high performance components and processes dedicated to the needs of VCSEL array chips in high power systems. New approaches help to eliminate components and process steps and make the system more robust and easier to manufacture.

Spatial mode phase locking in a laser diode bar

Densely packed high power systems rely on perfectly matched microchannel coolers. New cooler concepts with integrated electrical and mechanical interfaces have been investigated and offer advantages for high power system design.

High efficiency, compact size and low price are some of the reasons for the wide spreading of high-power laser diode bars. However, laser diode bars have low beam quality due to their multiple emitters. One way to overcome this drawback is to obtain phase locking of the different emitters of the diode bar, which increases the beam quality and enables a smaller focused beam. Phase locking of diode lasers was previously demonstrated by Talbot effect [1], and off axis coupling [2]. However, these coupling methods work only for periodic emitters.

The bonding process of chips on sub-mounts and coolers has been studied extensively and for a variety of solder materials. High quality of the interfaces as well as good reliability under normal operation and thermal cycling have been realized. A viable alternative to soldering is sintering with a silver paste. The very positive results which have been achieved with rather different technologies indicate the robustness of the VCSEL chips and the suitability for high power systems. Beam shaping micro-optics can be integrated on the VCSEL chip in a wafer scale process by replication of lenses in a polymer layer. The performance of VCSEL arrays with integrated collimation lenses has been positively evaluated and the integrated chips are fully compatible with all further assembly steps. The integrated high power systems make the application even easier and more robust. New examples in laser material processing and pumping of solid state lasers will be presented.

We demonstrate passive phase locking technique of laser diode bars which is robust, stable and works with non-periodic diode bar emitters. We built a degenerate diode laser cavity of 906 nm wavelength and placed two CCD cameras for measuring the near field and far field intensity distributions. The degenerate cavity contains a diode bar with antireflection coating, a 4-f system and an output coupler. In order to phase lock the emitters of the diode bar, we insert a varying aperture into the focal plane of the 4-f system [3]. We measured the output beam quality and power as a function of the aperture width. Our results show that the beam quality can be improved by a factor of 2.7 with reduction of less than 30% of the output power. These results can lead to novel high power diode lasers with increased beam quality. The full experimental details and results will be presented. References:

9733-31, Session 7

Industrial grade assembly solution for micro optics utilized in high power diode laser stacks Daniel Zontar, Fraunhofer-Institut für Produktionstechnologie IPT (Germany); Harald Vogt, MA micro automation GmbH (Germany); Sebastian Haag, Tobias Müller, Sebastian Sauer, Christian Brecher,

Return to Contents

Shir Shahal, Hamootal Duadi, Moti Fridman, Bar-Ilan Univ. (Israel)

1. V. V. Apollono, S. I. Derzhavin, V. A. Filonenko et al. “High power laser diode array phase-locking” SPIE, 3889,134 (2000). 2. Z. Su, Q. Lou, J. Dong, J. Zhou and R. Wei, “Beam quality improvement of laser diode array by using off-axis external cavity” Opt. Express, 15, 11776 (2007). 3. N. Davidson, M. Nixon, E. Ronen, M. Fridman, and A. Friesem, “Phase locking large arrays of lasers” in Conference on Lasers and Electro-Optics 2012, OSA Technical Digest (online) (Optical Society of America, 2012), paper CTu3N.7.

+1 360 676 3290 · [email protected]

113

Conference 9733: High-Power Diode Laser Technology and Applications XIV

9733-33, Session PTue

Holographic 3D display based on laser recording and reconstruction Hongyue Gao, JIcheng Liu, Shanghai Univ. (China) Our work focuses on static and dynamic holographic 3D display bases on laser recording and reconstruction. Laser plays an important role in holography, and provides wider color than LED display. In this paper we will present some work on 3D hologram print and holographic 3D video display in materials, which aims at future 3D pictures and 3D displayers, because holography is a true 3D technique. Computer generated holograms, holographic storage materials, and hologram print system in holographic print study will be introduced. Furthermore, real time dynamic holographic 3D display in materials, which may be developed in holographic 3D televisions or holographic 3D projectors in future, will also be presented. More important, this is a very typical laser application because developments of holographic 3D displayers depend on development of lasers. We hope that more and more lase experts can pay attention to holographic 3D display by this presentation, and the holographic display can come into our lives as soon as possible, since holographic 3D display, as a true 3D display, has huge application area.

114

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI Monday - Tuesday 15–16 February 2016 Part of Proceedings of SPIE Vol. 9734 Vertical External Cavity Surface Emitting Lasers (VECSELs) VI

9734-1, Session 1

How we developed OP-VECSELs at Micracor (Invited Paper) Mark E. Kuznetsov, AXSUN Technologies Inc. (United States) Semiconductors have been used as laser gain medium since the earliest days of lasers. Current injection of carriers across a diode p-n junction has been the preferred way to pump such lasers, leading to the ubiquitous diode lasers used across a wide range of applications. Optical pumping of semiconductor lasers has also been used through the years, but mostly as a research tool on the path to the ultimately electrically pumped version. In the mid 1990s, a group led by Aram Mooradian in a small startup company Micracor demonstrated Optically Pumped Semiconductor Lasers (OPSL) with remarkable properties that led to their rapid development and wide use in research and industrial applications. Using vertical cavity configuration emitting light normal to the plane of the wafer, and applying an external mirror to stabilize a large area fundamental transverse mode, optical pumping allowed operation of watt-class lasers with excellent beam quality and wide wavelength coverage enabled by the bandgap-engineered semiconductor media. These Vertical External Cavity Surface Emitting Lasers (VECSEL) proved to be so versatile, that arrayed electrically-pumped version of these lasers, NECSEL, was developed in another startup company, Novalux, led again by Aram Mooradian. In this presentation I will describe our early work on OPSLs at Micracor, where we took the dreams of a new remarkable laser and found a path to make them a reality. We also remember Aram Mooradian as a person and scientist and his foundational contributions to the field of VECSEL lasers.

9734-2, Session 1

Evolution of the Novalux extended cavity surface-emitting laser (NECSEL) (Invited Paper) John G. McInerney, Univ. College Cork (Ireland) The NECSEL is a VECSEL based on an electrically pumped semiconductor gain element with integrated Bragg gratings and a single-ended external compound cavity for mode selection and coherence enhancement. Initially designed for 980 nm operation, it produced multi-watt quasi-CW outputs with M2 < 1.2. A hybrid integrated version produced ~0.1 W CW in a TOstyle can. Mode-locked versions of the full NECSEL produced ~1 ps pulses transform limited with ~0.1 kW peak powers. Subsequent designs used intracavity frequency doubling, initially using bulk nonlinear crystals for blue emission, later migrating to quasi-phasematched PPLN arrays as these became available.

9734-3, Session 1

Continuous-wave VECSELs: Review of recent progress (Invited Paper) Mircea Guina, Tampere Univ. of Technology (Finland) The development of continuous-wave VECSELs has reached a maturity level that enables deployment of a wide range of applications in spectroscopy, pumping and cooling of solid-state media, biophotonics, or laser projection, just to mention a few. During the past years, the most diverse and intense developments have aimed at reaching new wavelengths by deploying

Return to Contents

emerging semiconductor materials and related technologies for gain mirror fabrication. To this end we could mention the development of straincompensated GaInAs/GaAs gain mirrors, development of GaInNAsSb/ GaAs-based gain mirrors with wavelength coverage between 1.1 µm and 1.5 µm, development of InAs/GaAs QD-based mirrors, use of wafer bonding technology, development of GaInAsSb/GaSb gain mirrors with emission beyond 2 µm, or the emergence of InGaN/GaN-based VECSELs with emission at blue wavelengths. On the other hand, intracavity frequency doubling has enabled attaining power levels above 20W for wavelengths covering green, yellow, and orange bands. Major developments have been also made concerning generation of UV wavelengths as well as of THz radiation. Moreover, cavity stabilization techniques combined with wavelength selective elements, have enabled attaining high-power outputs with a narrow-linewidth, and eventually continuously tuneable, which are instrumental features for spectroscopic applications. The paper is focused on reviewing the major progress in continuous-wave VECSELs. Emphasis is put on advances concerning power scaling and related thermal management techniques, and wavelength coverage. The progress will be discussed in connection with established and emerging applications that have fostered the tremendous progress experienced by VECSEL technology during the last decade.

9734-4, Session 1

Ultrafast vertical external cavity surface emitting lasers (VECSELs) (Invited Paper) Ursula Keller, ETH Zürich (Switzerland) Aram Mooradian made pioneering contributions for a novel type of laser that has bridged the gap between semiconductor lasers and solidstate lasers. The high-power optically pumped vertical-external-cavity surface-emitting laser (VECSEL) combines the best of both worlds: the semiconductor gain medium allows for flexible choice of emission wavelength via bandgap engineering and good pump efficiency is obtained from fairly low-cost, low-beam-quality high-power diode laser bars into a near-diffraction-limited output beam. The VECSEL is part of the family of VCSELs which are the most frequently manufactured semiconductor lasers today. In contrast to a VCSEL a VECSEL has an external cavity and is either optically or electrically pumped. VECSELs also have been passively modelocked using a semiconductor saturable absorber mirror (SESAM). The MIXSEL (i.e. modelocked integrated external-cavity surface emitting laser) combines the gain of VECSELs with the saturable absorber of a (SESAM) in a single semiconductor device. Hence, self-starting and stable passive modelocking is obtained in a simple straight cavity formed by the semiconductor chip and a curved output coupler. The VECSEL and MIXSEL are part of the family of ultrafast semiconductor disk lasers which rapidly advanced over the last decades. The strong interest from industry for inexpensive, compact and reliable ultrafast laser sources in the picosecond and femtosecond domain has driven this technology towards first commercial products. Frequency metrology and biomedical applications would benefit from sub-200 femtosecond pulse durations with peak powers in the kilowatt range. This talk is a tribute to Aram Moradian and will give an overview of the recent advances.

9734-5, Session 2

Gigahertz dual-comb modelocked diodepumped semiconductor and solid-state lasers (Invited Paper) Sandro M. Link, Mario Mangold, Matthias Golling,

+1 360 676 3290 · [email protected]

115

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI Alexander Klenner, Ursula Keller, ETH Zürich (Switzerland) One passively modelocked laser can simultaneously generate two gigahertz, orthogonally polarized and collinear frequency combs with slightly different but adjustable pulse repetition rates. This is successfully demonstrated for both, a semiconductor disk laser (SDL), also referred to as vertical external cavity surface emitting laser (VECSEL) and a solid-state Nd:YAG laser, each pumped with the same multimode diode array pump laser. This laser uses an intracavity birefringent crystal, which splits the one cavity beam into two spatially separated and orthogonally polarized beams. The SDL is a modelocked integrated external-cavity surface emitting laser (MIXSEL) that combines the saturable absorber of a SESAM with the gain of a VECSEL in a single semiconductor structure and enables dual-output operation in a simple linear straight cavity. The demonstration of dual-polarized output with the Nd:YAG laser extends this technique to ion-doped solid-state laser technologies. Such compact and cost-efficient dual-comb sources are interesting for spectroscopic applications. The microwave frequency comb, generated by the optical beat of the two orthogonal pulse trains, can be used to down-convert the terahertz optical frequencies into the electronically accessible microwave regime. The comb is detected simply by superimposing the two beams in the same polarization on a photodetector. Using a second birefringent crystal of same length but with the optical axis rotated by 90° results in two pulse trains with the same pulse repetition frequency, allowing to directly detect and characterize the relative carrier envelope offset (CEO) frequency dynamics. The stabilization and noise characterization of the dual comb laser will be presented.

9734-6, Session 2

Recent progress in high-power ultrafast MIXSELs Cesare G. E. Alfieri, Dominik Waldburger, Sandro M. Link, Emilio Gini, Matthias Golling, Bauke W. Tilma, Mario Mangold, Ursula Keller, ETH Zürich (Switzerland) A modelocked integrated external cavity surface emitting laser (MIXSEL) is the most simple and compact type of ultrafast semiconductor disk laser, as it is operated in a straight linear cavity. High-power ultrafast MIXSELs offer highest repetition rate flexibility together with high performance in terms of pulse duration, average and peak power and are thus ideal candidates for applications in the fields of metrology and imaging. Here, we present the first sub-300-fs MIXSEL, fabricated by a regrowth scheme in MOVPE and MBE. The structure includes a lower field enhancement in the gain and an improved dispersion. We obtained 235 mW of average output power at a wavelength of 1044 nm and a repetition rate of 3.35 GHz. A pulse duration of 253 fs was retrieved from frequencyresolved optical gating measurements. The resulting 240-W peak power is the highest from a MIXSEL thus far. At 10 GHz repetition rate, we obtained a pulse duration of 279 fs and 310 mW of average output power. In addition, we developed MOVPE-grown saturable absorbers with fast recovery dynamics that were subsequently implemented in the first entirely MOVPE-grown MIXSEL. This MIXSEL delivered 1.56 W of average output power with 15.4 ps pulses at a repetition rate of 3.66 GHz. In a different configuration pulses as short as 2.6 ps with 301 mW of average output power at 5.84 GHz repetition rate were obtained. MOVPE-growth not only reduces growth complexity and losses introduced by regrowth of a MIXSEL, but also makes the technology more accessible for the optoelectronics industry.

Andrew P. Turnbull, Univ. of Southampton (United Kingdom); Markus Polanik, Univ. Ulm (Germany); Edward A. Shaw, Theo Chen Sverre, Univ. of Southampton (United Kingdom); Peter Unger, Univ. Ulm (Germany); Anne C. Tropper, Univ. of Southampton (United Kingdom) We present a VECSEL based on a gain sample design which utilizes only a single layer dielectric Al2O3-coating for dispersion management. The calculated GDD, over a 30-nm range around the lasing wavelength of 1035 nm, was -38 ± 33 fs2. The gain structure generated in combination with a surface-recombination SESAM pulse durations down to 193 fs with an average power of 400 mW at 1.6 GHz with an incident pump power of 30 W, setting a new peak power record for sub-200 fs mode-locked VECSELs. The obtained sech2-pulses were not transform-limited and had a timebandwidth product of up to 0.64. A subsequent FROG analysis of the pulse train revealed significant higher-order chirp characteristics. In order to investigate where the higher-order dispersion components arise from pulse trains generated by various VECSELs, with similar gain chip layer designs that have only small differences, have been investigated using the FROG analysis. An optimized gain chip design for higher-order dispersion management could reduce the time bandwidth product and thus further push the pulse duration towards the 100-fs mark, at which point VECSELs become an interesting source for applications such as direct GHz frequency comb generation.

9734-8, Session 2

Pulse shortening of an ultrafast VECSEL Dominik Waldburger, Cesare G. E. Alfieri, Sandro M. Link, Emilio Gini, Matthias Golling, Mario Mangold, Bauke W. Tilma, Ursula Keller, ETH Zürich (Switzerland) Ultrafast, optically pumped, vertical external-cavity surface-emitting lasers (VECSELs) are excellent sources for industrial and scientific applications that benefit from compact semiconductor based high-performance lasers with gigahertz pulse repetition rates and excellent beam quality. Applications such as self-referenced frequency combs and multi-photon imaging could benefit from sub 150-fs pulse durations combined with high pulse peak power. Here, we present our recent progress in sub-150-fs semiconductor saturable absorber mirror (SESAM) modelocked VECSELs. In order to obtain the short pulse durations, we utilized precise dispersion engineering and an active region designed for broadband gain. Furthermore, a low and flat average field enhancement of the active InGaAs quantum wells of ≈ 0.5 (normalized to 4 outside the structure) ensures high gain saturation fluences. In combination with a SESAM with fast recovery dynamics, 128-fs pulses with 303 W of pulse peak power were obtained. The average output power was 80 mW with a pulse repetition rate of 1.8 GHz at a central wavelength of 1033 nm. In a similar configuration 147-fs pulses with 328 W of pulse peak power have been achieved. Both laser configurations operated in a fundamental transverse mode with an M2 value of 50-mW average power regime. With full characterization of the gain and saturable absorber parameters, we can identify current limitations of our ultrafast VECSELs and present guidelines to maintain the short pulse durations while scaling the technology to even higher pulse peak power.

9734-7, Session 2

High-order dispersion in sub-200-fs pulsed VECSELs Christopher R. Head, Univ. of Southampton (United Kingdom); Alexander Hein, Univ. of Ulm (Germany);

116

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI

9734-9, Session 2

[1] P. Holl et al, IEEE J Sel Top Quantum Electron. 21 (6), (2015).

Advances in low-repetition-rate modelocked semiconductor disk lasers in multi-pass cavity geometries (Invited Paper) Loyd J. McKnight, Peter J. Schlosser, Alexander A. Lagatsky, Martin D. Dawson, John-Mark Hopkins, Fraunhofer Ctr. for Applied Photonics (United Kingdom) Modelocked semiconductor disk lasers (SDLs) offer a low-cost, compact and versatile solution for nonlinear microscopy, however, the desirable repetition rate of 80-100 MHz is hard to achieve without the short carrier lifetime in the semiconductor gain chip causing multiple pulsing effects or a drop in efficiency. We have developed a number of novel multi-pass cavities that solve this problem by passing the intracavity beam through the optically pumped gain region multiple times per round trip of the cavity. This has the effect of reducing the time between intracavity pulses hitting the gain region whilst ensuring a clean and efficient low repetition rate output. Using 8 passes of the gain region per round trip we achieved a repetition rate of 86 MHz offering output powers above 120 mW and pulse durations of 2.2 ps. This represents a peak power greater than 500 W whilst maintaining gain and semiconductor saturable absorber mirror (SESAM) chips at room temperature. A number of cavities will be presented including those with repetition rates of 112 MHz and 230 MHz with similar power levels and pulse durations. For this work we designed antiresonant SDL gain wafers at a wavelength of ~955 nm, capable of efficiently exciting green fluorescent protein in a two-photon process, and a surface-recombination SESAM that offers a fast relaxation time. Details of the novel cavities and the gain and SESAM structures will be presented including a comprehensive characterization of the clean modelocked operating regime.

9734-10, Session 3

Single frequency 2-3 micron VECSELs (Invited Paper) Marcel Rattunde, Peter Holl, Steffen Adler, FraunhoferInstitut für Angewandte Festkörperphysik (Germany); Sebastian Kaspar, AIM INFRAROT-MODULE GmbH (Germany); Andreas Bächle, Elke Diwo, Rolf Aidam, Wolfgang Bronner, Joachim Wagner, Fraunhofer-Institut für Angewandte Festkörperphysik (Germany) Narrow-linewidth, tunable laser sources in the 2 – 3 µm wavelength range are of special interest for a range of applications such as gas analysis, remote sensing, LIDAR, optical free-space communication, laser seeding as well as for fundamental research like quantum optical experiments. Vertical external cavity surface emitting lasers (VECSEL) based on the (AlGaIn)(AsSb) materials system are ideally suited to serve these needs. High-efficient, high-power gain mirrors are available [1,2] and by including wavelength-selective elements in the laser cavity, narrow-linewidth singlefrequency emission and wavelength tunability can be achieved [3]. Without active stabilization, the emission-linewidth of the VECSEL can be well below 100 kHz and by scaling the pump- and mode-spot to larger diameters, over 2W (3W) single-frequency emission could be achieved at 2.0 µm and 20°C (3°C) heatsink temperature [4]. In this presentation recent advances concerning these single-frequency sources will be reviewed with special emphasis on the different mounting and heat extraction technologies for the VECSEL chip and their influence on the spectral properties and the VECSEL efficiency. Further on, alternative approaches for wavelength control (such as self-seeding) will be presented and discussed, together with a requirement analysis for the different applications. References

Return to Contents

[2] J. Paajaste et al., J. Cryst. Growth 311, 1917 (2009) [3] O. Ochotnikov, Ed., “Semiconductor Disk Laser”, Wiley-VCH, 2010 [4] S.Kaspar et al., IEEE JSTQE 19, 1501908 (2013)

9734-11, Session 3

Industrial integration of high coherence tunable single frequency semiconductor lasers based on VECSEL technology for scientific instrumentation in NIR and MIR Stephane Denet, Innoptics SAS (France); Baptiste Chomet, Univ. Montpellier 2 (France); Vincent Lecocq, Laurence Ferrières, Innoptics SAS (France); Mikhaël Myara, Laurent Cerutti, Univ. Montpellier 2 (France); Isabelle Sagnes, Lab. de Photonique et de Nanostructures (France); Arnaud Garnache, Univ. Montpellier 2 (France) Applications such as spectroscopy, lidar, or velocimetry require highly coherent tunable laser sources. The Vertical External Cavity Surface Emitting Laser (VECSEL) III-V semiconductor technology is a good candidate, with promising lab results already demonstrated. Inside a research group gathering expertise in chip design and epitaxy, laser cavity design, compact and robust laser packaging and noise measurements, we are currently developing a family of VECSEL-based modules, in the 0.8-1.1 µm (GaAs-based) and 2-2.5 µm (Sb-based) spectral windows, with future developments at 1.5 µm. We are presenting here tunable single frequency modules at 1 µm and 2.3 µm. Featuring a ? VCSEL chip being part of a sub-mm laser cavity, the modules also comprise a compact system for optical pumping, means for laser temperature monitoring, and a monitoring photodiode. At 1 µm we demonstrate high power (> 60mW), high coherence, low divergence diffraction limited TEM00 beam, high spectral purity (SMSR >55dB) and linear polarization (50dB PER), while at 2.3 µm broadband continuous tuning (> 7nm) and overall tunability of 80 nm are achieved. Those performances can be reached thanks to a high finesse cavity associated with ideal homogeneous QW gain behavior. In addition, the design without any intracavity element offers a robust single frequency regime with a good long term wavelength stability. Ongoing developments intend to enhance the main specifications for each application (tunability at 2.3 µm and low noise at 1 µm). Dedicated control electronics are also under development in order to improve laser stability.

9734-12, Session 3

Dual-frequency VECSELs for microwave photonics applications (Invited Paper) Fabien Bretenaker, Lab. Aimé Cotton (France) and Ecole Normale Supérieure de Cachan (France) Optical generation of tunable high-purity radio-frequency (RF) signals is essential for the future optoelectronic communication systems such as broadband mobile systems [1], satellite networks [2], long-range transmission of high purity radio-frequency (RF) references, etc. One way to generate such low noise optically carried RF signals is to build two-frequency lasers. In this case, the beatnote between the two optical frequencies provides the desired RF signal. This approach has been applied in the case of solid-state lasers [3,4]. But, in this case, the excess noise induced by the laser relaxation oscillation noise is detrimental to the spectral purity of the carried RF signal. However, recently, optically pumped Vertical External Cavity Surface Emitting Lasers (VECSELs) have been shown to obey the class-A regime, i. e., to exhibit no relaxation oscillations. These

+1 360 676 3290 · [email protected]

117

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI lasers are thus capable of emitting a single-frequency with an ultralow intensity noise [5-7]. Our aim here is to show how such VECSELs can be made to oscillate in dual-frequency regime [8,9], and to report our recent efforts to elucidate the physical mechanisms that give rise to the phase noise observed in the generated RF signal [10,11,12]. 1. D. C. Ni, H. R. Fetterman, and W. Chew, IEEE Trans. Microwave Theory Technol. 38, 608 (1990). 2. U. Gliese, E. L. Christensen, and K. E. Stubkjaer, J. Lightwave Technol. 9, 779 (1991). 3. M. Alouini, B. Benazet, M. Vallet, M. Brunel, P. Di Bin, F. Bretenaker, A. Le Floch, and P. Thony, IEEE Photon. Tech. Lett. 13, 367 (2001). 4. G. Pillet, L. Morvan, M. Brunel, F. Bretenaker, D. Dolfi, M. Vallet, J.-P. Huignard, and A. Le Floch, J. Lightwave Technol. 26, 2764 (2008). 5. G. Baili, M. Alouini, D. Dolfi, F. Bretenaker, I. Sagnes, and A. Garnache, Opt. Lett. 32, 650 (2007). 6. G. Baili, F. Bretenaker, M. Alouini, L. Morvan, D. Dolfi, and I. Sagnes, J. Lightwave Technol. 26, 952 (2008). 7. G. Baili, L. Morvan, G. Pillet, S. Bouchoule, Z. Zhao, J.-L. Oudar, L. Ménager, S. Formont, F. Van Dijck, M. Faugeron, M. Alouini, F. Bretenaker, and D. Dolfi, J. Lightwave Technol 32, 3489 (2014). 8. G. Baili, L. Morvan, M. Alouini, D. Dolfi, F. Bretenaker, I. Sagnes, and A. Garnache, Opt. Lett. 34, 3421 (2009). 9. F.A. Camargo, J. Barrientos, G. Baili, L. Morvan, D. Dolfi, D. Holleville, S. Guerandel, I. Sagnes, P. Georges, and G. Lucas-Leclin, Opt. Lett. 34, 3421 (2009). 10. S. De, V. Pal, A. El Amili, G. Pillet, G. Baili, M. Alouini, I. Sagnes, R. Ghosh, and F. Bretenaker, Opt. Expr. 21, 2538 (2013). 11. S. De, A. El Amili, I. Fsaifes, G. Pillet, G. Baili, F. Goldfarb, M. Alouini, I. Sagnes, and F. Bretenaker, J. Lightwave Technol. 32, 1307 (2014). 12. S. De, G. Baili, S. Bouchoule, M. Alouini, and F. Bretenaker, Phys. Rev. A 91, 053828 (2015).

9734-13, Session 3

Laser cooling of trapped ions using a frequency quadrupled VECSEL Shaun C. Burd, National Institute of Standards and Technology (United States) and Univ. of Colorado at Boulder (United States); Tomi Leinonen, Jussi-Pekka Penttinen, Optoelectronics Research Ctr. (Finland); David T. Allcock, National Institute of Standards and Technology (United States); Raghavendra Srinivas, National Institute of Standards and Technology (United States) and Univ. of Colorado at Boulder (United States); Daniel H. Slichter, Andrew C. Wilson, Dietrich Leibfried, National Institute of Standards and Technology (United States); Mircea Guina, Optoelectronics Research Ctr. (Finland); David J. Wineland, National Institute of Standards and Technology (United States) and Univ. of Colorado at Boulder (United States) The recent advances in the field of quantum information processing have paved the way for high performance computing and high precision measurements of physical parameters. These developments rely on laser cooling of atoms and ions using narrow-linewidth, resonantly tuned lasers. Vertical-external-cavity surface-emitting laser (VECSEL) system device geometry enables the combination of single-frequency operation and good beam quality with the wavelength versatility of semiconductors, which are advantageous features for these applications. Here we report on laser cooling and high precision spectroscopy of trapped Magnesium ions using a frequency quadrupled VECSEL.

emitting gain chip. The gain chip had ten 7-nm-thick GaInAs quantum wells, with an indium mole fraction of 35%. The accumulation of net strain was eliminated by using GaAsP strain compensation layers. An intra-cavity birefringent filter and an etalon were used to achieve single frequency operation and wavelength tuning. The laser line-width was measured to be less than 140 kHz using a heterodyne measurement with a narrow linewidth fiber laser. The laser was stabilized against long term drifts using a frequency offset lock between the VECSEL and the fiber laser (which was stabilized to a Doppler free transition in molecular Iodine) or a direct lock to an Iodine transition. Second harmonic generation in a waveguide doubler produced up to 350mW at 559nm which was subsequently frequency doubled in an external build up cavity to produce up to 22mW in the UV at 280nm. The system was used to Doppler-cool a single 25 Mg ion in an RF Paul trap on the S1/2 |3,3>->P3/2 |4,4> transition. The slightly saturated and residually Doppler-broadened line width of this transition was measured to be 45MHz. The laser was also tuned to 1121nm to perform high resolution spectroscopy of the S1/2 |2,2>->P1/2 |3,3> transition. This work demonstrates the versatility of VECSELs in high precision spectroscopy of trapped atoms and provides a scalable laser source for the development of ion trap quantum information processors.

9734-14, Session 4

Generation of new spatial and temporal coherent light states using III-V semiconductor laser technology: VORTEX, continuum, dual frequency for THz (Invited Paper) Arnaud Garnache, Mohamed Seghilani, Romain Paquet, Mohamed Sallhai, Baptiste Chomet, Mikhael Myara, Stephane Blin, Univ. Montpellier 2 (France); Isabelle Sagnes, Gregoire Beaudoin, Luc Legratiet, LPN CNRS (France); Philippe Lalanne, LP2N IOGS (France) Since years, the VeCSEL concept is pointed out as a technology of choice for beyond-state-of-the-art laser light sources, demonstrating wavelength flexibility, high power, high spatial and temporal coherence, linear polarization state, CW or ultra-short pulsed operation, compactness and functionalities. The targeted coherent state is typically the gaussian TEM00, single frequency, linearly polarized light state. In this work, we take advantage of the VeCSEL technology for generation of new kinds of coherent states, thanks to insertion of intracavity functions based on flat photonics. These new coherent states target many applications including optical tweezers, telecommunications, fundamental physics, sensors… A first part of this work aims at demonstrating new spatial domain coherent state. We developed a semiconductor flat photonic technology for intracavity transverse phase and intensity control. Intensity control is obtained thanks to sub-wavelength metallic masks. For phase control, we developed an ultra-low loss metamaterial technology. This technological development permitted generation and control of high coherence single or dual high order Laguerre-Gauss mode, VORTEX or Hermite-Gauss mode, preserving the spatial and temporal coherence properties of usual TEM00 VeCSELs. It paves the way for the generation of new coherent beams and functionalities: wavelength filtering, dual frequency for THz source. In a second part, we explore new time domain coherent state: owing to a high gain semiconductor chip design and insertion of an intracavity acousto-opticfrequency-shifter, we demonstrated and studied the first semiconductorbased low noise broadband modeless laser, with a 300 GHz band and a coherence length of 4km.

Light at 1118nm was generated using an I-cavity VECSEL with a bottom

118

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI

9734-15, Session 4

9734-17, Session 4

Terahertz quantum cascade VECSEL

Widely tunable DBR-free semiconductor disk laser

Luyao Xu, Christopher A. Curwen, Philip W. C. Hon, Tatsuo Itoh, Benjamin S. Williams, Univ. of California, Los Angeles (United States) Vertical-external-cavity surface-emitting lasers (VECSELs) have been successfully used in the visible and near-infrared to achieve high output power with excellent Gaussian beam quality. However, the concept of VECSEL has been impossible to implement for quantum-cascade (QC) lasers, since the optical gain is based on intersubband transitions of electrons, which only interact with the electric field polarized perpendicular to the quantum wells plane according to the “intersubband selection rule”. In this work we demonstrated a terahertz (THz) quantum cascade external cavity laser, which is also the first VECSEL in the terahertz regime. The enabling component for the QC-VECSEL is an amplifying metasurface reflector composed of a sparse array of metallic sub-cavities, which allows the normally incident radiation to interact with the electrically pumped QC gain medium. The QC-VECSEL is implemented in a plano-plano Fabry-Perot cavity, with a wire-grid polarizer as its output coupler. A beam of 4.3° ? 5.1° FWHM divergence and a near-Gaussian profile is observed with an output power > 5 mW. THz QC-lasers have often been characterized by poor beam quality due to their sub-wavelength metallic waveguides. The symmetry and circularity of the beam are further improved by placing an aperture into the cavity. Our work on THz QC-VECSEL initiates a new approach towards achieving scalable output power in combination with a diffraction-limited beam pattern for THz QC-lasers. Furthermore, the intra-cavity access of the VECSEL gives tremendous versatility to QC-lasers, such as the ability for mode engineering.

9734-16, Session 4

1.2?m emitting VECSEL based on type-II aligned QWs Christoph Möller, Christian Berger, Christian Fuchs, Philipps-Univ. Marburg (Germany); Antje Ruiz Perez, NAsP III/V GmbH (Germany); Stephan W. Koch, Philipps-Univ. Marburg (Germany); Jörg Hader, Jerome V. Moloney, Nonlinear Control Strategies (United States); Wolfgang Stolz, Philipps-Univ. Marburg (Germany) and NAsP III/V GmbH (Germany) Since the invention of VECSELs, their great spectral coverage has been demonstrated and emission wavelengths in the range from UV to almost MIR have been achieved. However, in the infrared regime the laser performance is affected by Auger losses which become significant at large quantum defects. In order to reduce the Auger losses and to develop more efficient devices in the IR, type-II aligned QWs have been suggested as alternative gain medium for semiconductor lasers. We present the first room temperature VECSEL containing type-II aligned quantum wells arranged as resonant periodic gain. The quantum wells consist of (GaIn)As/Ga(AsSb)/(GaIn)As heterostructures. The structure was grown bottom-up on GaAs substrate and flip-chip bonded onto a diamond heat spreader. The device, pumped at 808 nm, emits >1 W of cw output power at an emission wavelength of 1.2 ?m. A detailed study of the device is performed in order to investigate the potential of such novel type-II gain media for future applications. These investigations include the determination of the power and temperature dependent shift rates. The gain temperatures at laser threshold and at maximum output power are determined. Furthermore, edge photoluminescence and reflectivity measurements are performed in order to accurately determine the detuning. These experimental results are compared with fully microscopic simulations.

Return to Contents

Zhou Yang, Alexander R. Albrecht, The Univ. of New Mexico (United States); Jeffrey G. Cederberg, Sandia National Labs. (United States); Shawn Hackett, The Univ. of New Mexico (United States) and Air Force Research Lab. (United States); Mansoor Sheik-Bahae, The Univ. of New Mexico (United States) Semiconductor disk lasers (SDLs) have gained lots of attention due to their wavelength flexibility and high output powers. With the external cavity configuration, they are superior to edge-emitting semiconductor lasers for applications requiring intra-cavity optical elements, like non-linear crystals for frequency conversion or saturable absorbers for mode-locking. Theoretically, SDL is power scalable but the low thermal conductivity semiconductor DBR impedes the heat removal process. For DBR-free SDLs, a multi-quantum-well (MQW) active region is grown on a substrate with a sacrificial layer. Then the MQW is lifted off and van der Waals bonded onto transparent high thermal conductivity substrates, such as diamond. Without a need for lattice-matched semiconductor distributed Bragg reflectors (DBRs), these SDLs can be realized in more material systems and cover a wider wavelength range. Also, the tuning range would no longer be limited by the high-reflection bandwidth of the DBR, but instead by the broader high reflection band of the external dielectric mirrors. Based on thermal analysis, the DBR-free geometry with diamond heatspreaders on both sides of the active region has advantages in thermal management over traditional SDLs. For an InGaAs MQW sample bonded to one single-crystalline CVD diamond, preliminary experiments show a record 78 nm tuning range centered at 1150nm. The CW output power at 1150 nm was 2.5 W. For another active region, 4 W output power (limited by the available pump power) is collected at 1040 nm. Currently efforts are underway to improve laser performance and power scaling by mitigating intracavity losses.

9734-18, Session 5

Resonant measurements of nonlinear lensing in a VECSEL gain sample (Invited Paper) Adrian H. Quarterman, Univ. of Dundee (United Kingdom); Edward E. Shaw, Univ. of Southampton (United Kingdom); Keith G. Wilcox, Univ. of Dundee (United Kingdom) In recent years there have been several reports describing self-modelocking (SML) in vertical-external-cavity surface-emitting lasers (VECSELs). Some of these reports have suggested that the behaviour that has been observed results from nonlinear lensing in the VECSEL gain sample in a manner analogous to Kerr lens modelocking in solid state lasers. However to date none of the groups that have reported SML in VECSELs have performed measurements to ascertain whether nonlinear lensing occurs in the gain sample. Measurements of nonlinear lenses in VECSEL gain samples are therefore of value not only in order to understand the behaviour observed in the reports of SML, but also as a potentially crucial design tool for any mode-locked VECSEL, regardless of the modelocking method used. In a previous publication [1] we described measurements which demonstrated that a defocussing nonlinear lens was present in an unpumped VECSEL gain sample, and that the inverse focal length of the lens increased with pump power, to the point of becoming a focussing lens for sufficiently high pump powers. Unfortunately, by necessity this measurement was performed using a probe laser which was not resonant with the quantum wells in the sample, meaning that the values measured may well be different from those experienced under operating conditions in a VECSEL. This paper will describe a more complete characterisation of VECSEL gain sample nonlinear lensing with a probe laser whose wavelength

+1 360 676 3290 · [email protected]

119

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI is resonant with the gain sample quantum wells. [1] Quarterman et al. Applied Physics Letters, 106, 011105 (2015).

9734-19, Session 5

Ultrafast characterization of semiconductor gain and absorber devices for mode-locked VECSELs Caleb Baker, Maik Scheller, Hwang-Jye Yang, College of Optical Sciences, The Univ. of Arizona (United States); Stephan W. Koch, College of Optical Sciences, The Univ. of Arizona (United States) and Philipps-Univ. Marburg (Germany); Ronald J. Jones, Jerome V. Moloney, College of Optical Sciences, The Univ. of Arizona (United States); Antje Ruiz Perez, Wolfgang Stolz, Philipps-Univ. Marburg (Germany); Sadhvikas Addamane, Ganesh Balakrishnan, The Univ. of New Mexico (United States) As Vertical External-Cavity Surface-Emitting Lasers (VECSELs) become increasingly interesting candidates among the ultrafast class of modelocked sources, better understanding of their carrier dynamics on ultrafast timescales is necessary. To this end, we present a comprehensive characterization of semiconductor gain and absorber devices utilizing novel measurement techniques to supplement traditional pump and probe measurements. For our studies, we utilize a mode-locked, amplified, ytterbium fiber laser emitting 12nJ pulses with a bandwidth centered at 1040nm and a pulse duration of 120fs as probe laser source. The pulses are spectrally broadened in a single-mode fiber to cover the wavelength range between 940nm to 1100nm. The resulting pulses are compressed using a pulse shaper to a pulse duration of 20fs. The pulse shaper is also used to spectrally resolve measurements by creating 100fs pulses with varying center wavelengths to interact with the samples. Time resolution in the few femtosecond range results from traditional pump and probe measurements performed on VECSEL and SESAM samples with different designs. In-situ characterizations based on an asynchronous optical sampling technique of VECSEL samples mode-locked in the sub-500fs regime reveal additional long time recoveries of the gain present in real lasing condition. Our results indicate that multiple carrier relaxation mechanisms exists ranging in timescale from hundreds of femtoseconds to pico- and nanosecond regimes which affect the stability of mode-locking states as well as the pulse duration. Our study can contribute to development design strategies to optimize the gain chips and absorbers for further performance improvements.

9734-20, Session 5

Reflection z-scan measurements of the non-linear lens in VECSEL gain structures Edward A. Shaw, Univ. of Southampton (United Kingdom); Adrian Quarterman, Univ. of Dundee (United Kingdom); Andrew P. Turnbull, Theo Chen Sverre, Christopher R. Head, Anne C. Tropper, Univ. of Southampton (United Kingdom); Keith G. Wilcox, Univ. of Dundee (United Kingdom) Recent advances in thermal management of VECSEL gain structures using ‘flip-chip’ bonding have enabled the use of much higher pump densities than were previously possible. This has led to the achievement of record high output powers for both continuous-wave and mode-locked VECSELs. High pump densities have been associated with the observation of self-

120

mode-locking regimes, thought to arise from a non-linear lens in the VECSEL gain structure. Recently, the first measurement of the non-linear lens in a gain chip showed that the power and sign of the lens depends sensitively on the pumping conditions. The photon energy of the probe laser used in these measurements was less than the band gap energy of the quantum wells. Third-order refractive indices in semiconductors, however, are known to vary rapidly with the photon energy around the band gap. Here we present reflection z-scan measurements that probe the quantum well structure slightly above the band gap, in resonance with the typical operating wavelength of the laser. The strength of the non-linear lens is experimentally determined at pump densities and with pulse fluences approaching values typical for SESAM mode-locked VECSELs.

9734-21, Session 5

Self-mode-locked vertical-external-cavity surface-emitting laser (Invited Paper) Arash Rahimi-Iman, Mahmoud Gaafar, Christoph Möller, Max Vaupel, Fan Zhang, Dalia Al-Nakdali, Philipps-Univ. Marburg (Germany); Ksenia A. Fedorova, Aston Univ. (United Kingdom); Wolfgang Stolz, Philipps-Univ. Marburg (Germany) and NAsP III/V GmbH (Germany); Edik U. Rafailov, Aston Univ. (United Kingdom); Martin Koch, Philipps-Univ. Marburg (Germany) Within the last 15 years, a new class of pulsed lasers emerged which proved capable of generating ultrashort pulses. Semiconductor disk lasers, also referred to as vertical-external-cavity surface-emitting lasers (VECSELs), have become promising sources of fs-pulsed laser light which indeed can serve many applications, such as ultrafast spectroscopy, metrology, multiphoton microscopy, or material processing. Moreover, the externalcavity design of such lasers allow for versatility, compactness and beam quality – aspects which are all beneficial to the employment of VECSELs. However, with respect to a practical use, also robustness, flexibility and costefficiency play a role, which can be addressed via an approach referred to as saturable-absorber-free mode-locking, or self-mode-locking (SML). Much work has been performed in the field of saturable-absorber-based pulsed VECSELs by the community to provide ever shorter pulses using resonator-integrated or even chip-integrated semiconductor saturableabsorber mirrors (SESAMs), which have demonstrated an excellent performance of pulsed VECSELs with pulse durations in the range of 100 fs to picoseconds. Nevertheless, SML VECSELs can circumvent limitations naturally imposed on the device’s performance by SESAMs, which are costly and have to be individually designed for a certain operation wavelength. Here, we highlight recent achievements in the field of self-mode-locking of VECSELs with quantum-well as well as quantum-dot based gain media. Furthermore, assuming a nonlinear lensing effect to play a significant role for SML operation, we have studied the influence of a few VECSEL parameters on SML, such as power densities and cavity geometries, in the context of recent considerations of a nonlinear refractive index.

9734-22, Session 6

Narrow linewidth visible/UV semiconductor disk lasers for quantum technologies (Invited Paper) David Paboeuf, Brynmor E. Jones, Julio M. Rodríguez García, Peter J. Schlosser, Univ. of Strathclyde (United Kingdom); Dariusz Swierad, Joshua Hughes, Ole Kock, Lyndsie Smith, Kai Bongs, Yeshpal Singh, The Univ. of Birmingham (United Kingdom); Stefano Origlia, Stephan Schiller, Heinrich-Heine-Univ. Düsseldorf (Germany);

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9734: Vertical External Cavity Surface Emitting Lasers (VECSELs) VI Jennifer E. Hastie, Univ. of Strathclyde (United Kingdom)

9734-25, Session 6

Optically-pumped semiconductor disk lasers (SDLs) have been shown over the past decade to possess all the qualities required for quantum technology applications. Indeed the very specific dynamics of these lasers make them perfect candidates to achieve low intensity noise and sub-Hz linewidth. Moreover, bandgap engineering and nonlinear conversion allow very broad spectral coverage from the ultraviolet to the mid-infrared, while the external cavity provides an excellent beam quality.

A 1.5-W frequency doubled semiconductor disk laser tunable over 40 nm at around 745 nm

At the University of Strathclyde, we have been working for several years on GaInP based SDLs emitting in the 670-690 nm spectral band. Powers up to 1 W and single frequency emission have been achieved with these structures. By locking to a reference cavity, a relative frequency noise of 5 kHz (over 1 s) has been achieved, demonstrating the suitability of these sources for high coherence emission. This high coherence can be transferred to wavelengths in the UV by means of non-linear conversion. Such high coherence UV sources could find applications in UV photolithography or atmospheric spectroscopy. We recently started to develop laser sources suitable for quantum technologies, in particular the laser cooling of Strontium atoms within optical clocks. A power above 100 mW and relative frequency stability of 5 kHz has been achieved. This narrow linewidth laser at 689 nm has been moved to the University of Birmingham and used to trap millions of Sr atoms cooling down to ~170?K. This establishes the narrow linewidth and high spectral purity of the laser. Results and characterisation carried out will be provided.

9734-23, Session 6

InGaAs-QW VECSEL emitting >1300-nm via intracavity Raman conversion Daniele C. Parrotta, Riccardo Casula, Univ. of Strathclyde (United Kingdom); Jussi-Pekka Penttinen, Tomi Leinonen, Tampere Univ. of Technology (Finland); Alan J. Kemp, Univ. of Strathclyde (United Kingdom); Mircea Guina, Tampere Univ. of Technology (Finland); Jennifer E. Hastie, Univ. of Strathclyde (United Kingdom) We report intracavity Raman conversion of a long-wavelength InGaAs-QW VECSEL to ~1320nm, the longest wavelength ever achieved by a VECSELpumped Raman laser. The set-up consisted of a VECSEL capable of >17W at 1180nm and tunable from 1141-1203nm and 30mm-long KGd(WO4)2 (KGW) Raman crystal in a coupled-cavity Raman resonator. The Raman cavity was separated from the VECSEL resonator by a tilted dichroic mirror, which steers the Raman beam to an output coupler external to the VECSEL. The spectral emission of the VECSEL, and consequently of the Raman laser, is set by a 4mm-thick quartz birefringent filter in the VECSEL cavity. The KGW Raman laser is capable of emitting 2.5W at 1315nm, with M^2=2.5 and >4% diode-to-Stokes conversion efficiency. The Raman laser emission is tunable from 1295-1340nm, limited by the free spectral range of the birefringent filter. Spectral broadening of the fundamental emission is observed during Raman conversion. At the maximum output power the VECSEL, the total linewidth of the output spectrum is ~0.7nm FWHM. As a consequence, the Raman laser emission is also relatively broad (~0.9nm FWHM). Narrow (99.8%) attached to the gain medium, and is usually realized with a semiconductor Distributed Bragg Reflector (DBR). However, to reach the reflectivity needed, one has to use lattice matched semiconductor materials with high contrast refractive index, which can be challenging especially with InP based materials. Even with GaAs based material, one has to use 24 pairs of GaAs/AlAs to reach a reflectivity of 99.8%. This relatively thick DBR stack has a poor thermal conductivity and is a major limitation for high power diamond bonded VECSELs. Here, we demonstrate the realization of a low thermal impedance hybrid metal-semiconductor mirror VECSEL. We used only 14 pairs of AlGaAs/AlAs, transparent at the pump wavelength of 808nm, and we used a patterned mask to deposit pure gold on areas of the chip to be pumped, and Ti/Au on some other area to circumvent the poor adhesion of gold on GaAs. The addition of this metallic mirror requires the DBR region to be finished with an optical phase matching layer. A higher gain is observed on area metallized with pure gold and an output power of 4W at 1050nm was obtained with an rms fluctuation < 1% over 1 hour of operation. No lasing was obtained on areas metallized with Ti/ Au, showing the effectiveness of the metallic Au mirror and validating the bonding quality. Laser characteristics are studied in details and compared to simulations and chip processing will be discussed.

Vertical-external-cavity surface-emitting lasers (VECSELs) have been proven to be an excellent platform for the realization of high-power multi-mode or single-frequency continuous-wave operation, as well as mode-locked emission. Moreover, because of the emission-wavelength flexibility and the open cavity, this kind of laser is especially attractive to applications requiring intracavity frequency conversion. For instance, in order to develop a powerful continuous-wave terahertz source based on the differencefrequency generation in a VECSEL, several schemes have been realized to produce dual-wavelength emission. However, the separation of the two wavelengths hardly exceeds a few nanometers, being limited by the gain bandwidth of a single VECSEL chip, explaining the approach to go for multichip cavities. Here, we demonstrate a flexible and compact cavity design, which serially connects two different VECSEL chips in one cavity. Dual-wavelength emission with a wavelength separation of 10 nm and over 600 W intracavity power has been generated. Since the two wavelengths exhibit the same polarization, intracavity type-I second harmonic generation and sumfrequency generation have been performed in a LiNbO3 crystal. This design also shows the potential to offer dual-wavelength emission with other desirable wavelength separations, by employing different chip combinations and filters. Furthermore, we investigate the dependence between the emission wavelengths and intracavity incidence angles on the VECSEL chips, in order to extend the range of accessible wavelengths and thus splittings with this cavity design.

Return to Contents

+1 360 676 3290 · [email protected]

125

Conference 9735: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXI Monday - Thursday 15–18 February 2016 Part of Proceedings of SPIE Vol. 9735 Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXI

9735-1, Session 1

CIGS P3 scribes using ultra-short laser pulses and thermal annealing Gabor Matthäus, Klaus Bergner, Friedrich-Schiller-Univ. Jena (Germany); Mawuli Ametowobla, Andreas Letsch, Robert Bosch GmbH (Germany); Andreas Tünnermann, Stefan Nolte, Friedrich-Schiller-Univ. Jena (Germany) Thin-film photovoltaic panels are based on individual solar cells which are monolithically interconnected in series. These interconnections are commonly realized via mechanical micro scribing. In order to reduce the “dead area” represented by the interconnection zone and hence to increase the net solar output, tightly packed microscopic scribes have to be realized. For this reason, laser micro-machining gained increasing interest in recent years. However, regarding CIGS thin-film modules, the third structuring stage P3, which is responsible for isolating successive cells, in general suffers from decreased shunt resistance after laser processing. Here, we demonstrate high-impedance CIGS P3 scribes using ultrashort laser pulses and thermal annealing. During laser processing, we applied various ultra-short pulse laser systems, which delivered different pulse lengths (0.5 - 230 ps) at different wavelengths (388 - 1030 nm) at comparable pulse energies up to several microjoulses. We obtained a wide processing window which allowed a reliable structuring at very high speeds (?10 m/s). Immediately after laser processing, the samples revealed a significant drop in cell performance compared to mechanically processed reference cells, however, after thermal treatment, a permanent performance increase was achieved which outperformed the mechanically structured reference cells. In order to study the underlying annealing effect, we simulated the J-V characteristics using an equivalent circuit model yielding excellent agreement with our experimental results. We show, that the main drawback during ultra-short pulse processing is based on induced defect states at high densities. These defect states can be significantly reduced within minutes by thermal annealing at moderate temperatures.

9735-2, Session 1

Selective structuring of multi-layer functional thin films using a laser-induced shockwave delamination process Martin Ehrhardt, Pierre Lorenz, Lukas Bayer, LeibnizInstitut für Oberflächenmodifizierung e.V. (Germany); Carlos Molpeceres, Univ. Politécnica de Madrid (Spain); Carlos Antonio Herrera Ramirez, Abengoa Solar Espana SA (Spain); Klaus-Peter Zimmer, Leibniz-Institut für Oberflächenmodifizierung e.V. (Germany) The laser-assisted microstructuring of thin films, especially for electronic applications without damaging the layers or the substrates, is a challenge for laser micromachining techniques. The P3 scribing of copper indium gallium selenide (CIGS) solar cells on different carrier foil was studied using shock-wave-induced film delamination patterning (SWIFD). The delamination process is induced by a shock wave, generated by the laser ablation of the rear side of the carrier foil. The morphology and size of the resultant thin-film structures were studied by scanning electron microscopy (SEM) dependent on the laser parameters. Furthermore, the

126

composition after the laser treatment was analyzed by energy-dispersive X-ray spectroscopy (EDX). To demonstrate the practical functionality of the SWIFD process the solar cells were electrically characterized after the structuring process. Furthermore, to improve the physical understanding of the process, the delamination process was studied by shadowgraph experiments. The process was simulated using the finite element method, and the simulation results were compared with the experimental ones.

9735-3, Session 1

High throughput laser scribing of Cu(In,Ga)Se2 thin-film solar cells Andreas Burn, Christian Heger, Berner Fachhochschule Technik und Informatik (Switzerland); Stephan Bücheler, Shiro Nishiwaki, EMPA (Switzerland); David Bremaud, Roger Ziltener, Flisom AG (Switzerland); Lukas Krainer, Gabriel J. Spuehler, Onefive GmbH (Switzerland); Valerio Romano, Berner Fachhochschule Technik und Informatik (Switzerland) Solar cells based on Cu(In,Ga)Se2 absorbers show the highest efficiencies among all thin-film technologies. Their potential is underlined by efficiency world records of 21.7 percent, demonstrated on cell level (ZSW) and above 16 percent for an entire module (TSCM, Manz). In industrial production of CIGS solar modules, laser scribing is used for the monolithic interconnection of cells. However, different than in other fields of laser applications, laser scribing never improves solar cell performance but reduces active area, increases series resistance and decreases parallel resistance of the module which all reduce its performance. In the past years we conducted a comprehensive study on laser sources and parameters for selective ablation of photovoltaic thin-films. Various aspects have been analyzed and processes were validated in functional mini-modules. We have demonstrated 16.6 percent efficiency on an all-laser patterned, grid-less 8-cell mini-module. In this module we demonstrated low dead-zone interconnects of 2 compared to conventional focusing. Moreover, no significant broadening of the pulse spectra is observed, which is in excellent agreement with numerical simulations of the nonlinear pulse propagation and might favor SSTF for demanding applications such as intraocular fslaser surgery.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9736: Laser-based Micro- and Nanoprocessing X

9736-29, Session 7

Eternal 5D data storage by ultrafast laser writing in glass (Invited Paper) Peter G. Kazansky, Martynas Beresna, Jingyu Zhang, Rokas Drevinskas, Aabid Patel, Au?ra Cerkauskaite, Optoelectronics Research Ctr. (United Kingdom) Femtosecond laser writing in transparent materials has attracted considerable interest due to new science and a wide range of applications from laser surgery, 3D integrated optics and optofluidics to geometrical phase optics and ultra-stable optical data storage. A decade ago it has been discovered that under certain irradiation conditions self-organized subwavelength structures with record small features of 20 nm, could be created in the volume of silica glass. On the macroscopic scale the selfassembled nanostructure behaves as a uniaxial optical crystal with negative birefringence. The optical anisotropy, which results from the alignment of nano-platelets, referred to as form birefringence, is of the same order of magnitude as positive birefringence in crystalline quartz. The two independent parameters describing birefringence, the slow axis orientation (4th dimension) and the strength of retardance (5th dimension), are explored for the optical encoding of information in addition to three spatial coordinates. The slow axis orientation and the retardance are independently manipulated by the polarization and intensity of the femtosecond laser beam. The data optically encoded into five dimensions is successfully retrieved by quantitative birefringence measurements. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity and thermal stability up to 1000°. Even at elevated temperatures of 160oC, the extrapolated decay time of nanogratings is comparable with the age of the Universe - 13.8 billion years. The demonstrated recording of the digital documents, which will survive the human race, including the eternal copies of Kings James Bible and Magna Carta, is a vital step towards an eternal archive.

9736-30, Session 7

Surface treatment with small laser spots: an approach for the comparison of process parameters Stefan Kreling, Hinrich Grefe, Klaus Dilger, Technische Univ. Braunschweig (Germany) Pulsed lasers with spot diameters in the µm range are widely used for the aerial treatment of surfaces. Typical applications are cleaning of composite molds, paint stripping, laser heating or surface pre-treatment prior to adhesive bonding. In these cases the aerial treatment by small laser spots is achieved by overlapping the spots to lines in x-direction and the single lines to an area in y-direction. During this application the treatment result is significantly influenced by the distance between the single lines, called the hatch distance as well as the single spot overlap, which is defined by the ratio of spot diameter and pulse repetition rate to the line feed. Taking a closer look at this treatment strategy it becomes obvious that due to the overlapping of circular pulses an uneven distribution of the number of laser pulses which hit each aerial increment appears. The background of the approach taken here was the comparison of different pre-treatment parameters for adhesive bonding by calculating an accumulated energy, being the pulse energy multiplied by the average amount of pulses hitting each surface increment. The latter one was found using a numerical approach, depicting the distribution of laser pulses on the surface depending on the parameters spot size, pulse repetition rate, line feed and hatch distance. Based on the numerical model an empirical formula was derived which enables an easy calculation of the average number of laser pulses which hit each aerial increment of the surface. As an outlook some experimental results which were gathered using this

Return to Contents

approach for the surface pre-treatment of an adhesively bonded composite joint are given.

9736-31, Session 7

Extending ultrashort pulses laser texturing over large area Girolamo Mincuzzi, Marc Faucon, Rainer Kling, ALPhANOV (France) Surface Blackening by Ultra-Short Pulses Laser (UPL) texturing for industrial applications (aerospace, electronics, decoration etc.) passes through the use of both fast beam scanning systems and high repetition rate, High Power P, UPL. Nevertheless unwanted thermal effects are expected when P exceed some tens of W. An interesting strategy for a reliable heat management would consists in texturing with a low fluence values (slightly higher than the ablation threshold) and utilising a Polygon Scanner Heads delivering laser pulses with unrepeated speed. Here we show for the first time that over stainless steel, it is possible to obtain surface blackening by utilising a 2 MHz femtosecond laser jointly with a fast and accurate polygonal scanner head at relatively low fluence (0.11 J·cm-2). Different surface textures have been obtained varying the scan speed between 25 m·s-1 to 90 m·s-1. In particular, spikes formation process has been shown and optimised at 25 m·s-1 and a full morphology characterization by SEM has been carried out. Reflectance measurements carried out in visible and IR range (up to 2 µm) with integrating sphere will be presented to compare reference textures with high scan rate textures. In the best case a surface reflectance value < 5% has been extracted.

9736-32, Session 8

Nanofabrication of metals by interfering femtosecond laser processing and their applications (Invited Paper) Yoshiki Nakata, Noriaki Miyanaga, Osaka Univ. (Japan) In interfering femtosecond laser processing, energy is induced periodically according to an interference pattern. When a metallic thin film is processed, each spot in the interference pattern is partially melted, and then freezes due to a drop in temperature. The interference patterns change according to the phase shift and power ratio between the interfering beams, and are transcribed to the processed pattern. Furthermore, the temperature distribution of the film, which changes in time and space, governs the viscosity and surface tension. The resultant structures are very simple and unique, and include nanowhiskers, nanobumps, nanodrops, and metallic hole arrays. These can have applications in fields such as nanotechnology and metamaterial technology, for example, as plasmonic devices, such as surface-enhanced Raman spectroscopy templates. Our recent results will be presented.

9736-33, Session 8

Improved large area uniformity and production capacity of laser interference lithography with beam flattening device Yin-Kuang Yang, National Tsing Hua Univ. (Taiwan); YuXiang Wu, Te-Hsun Lin, Chun-Wen Yu, National Tsing Hua University (Taiwan); Chien-Chung Fu, National Tsing Hua Univ. (Taiwan) Laser interference lithography (LIL) is a maskless lithography technique with many advantages such as simple optical design, low cost, infinite depth of

+1 360 676 3290 · [email protected]

149

Conference 9736: Laser-based Micro- and Nanoprocessing X focus, and large area patterning with single exposure. However, the intensity of normal laser beam is Gaussian distribution. In order to obtain large area uniform structure, we have to expand the laser beam much larger than the wafer and use only the central part of the beam, resulting in wasting lots of energy and low production capacity. In this study, we designed a beam shaping device which consists of two parallel fused silicon optical windows with different coating on the opposite side. When the expanded laser beam pass through the device, the beam will experience several times of partial reflections between two optical windows, and the transmittance of laser beam will depends on the incident angle. The output intensity distribution will change from Gaussian distribution to a flat top distribution. In our experiment, we combined the beam shaping device with a Lloyd’s mirror LIL system. The results indicated that the LIL system with beam shaping device can obtain large area uniform pattern. And compare with the normal Lloyd’s mirror LIL system, the exposure time is shorten up to 5 times. In conclusion, this study design a beam shaping device for LIL system. The flat top beam produced by the device can improve the large area uniformity and the production capacity of traditional LIL system. Making LIL more suitable for industry application.

9736-34, Session 8

World record in high speed laser surface microstructuring of polymer and steel using direct laser interference patterning Valentin Lang, Teja Roch, Andres F. Lasagni, TU Dresden (Germany) and Fraunhofer IWS Dresden (Germany) Periodic surfaces structures with micrometer or submicrometer resolution produced on the surface of components can be used to improve their mechanical, biological or optical properties. In particular, these surfaces can control the tribological performance of parts, for instance in the automotive industry. In the last years, important efforts have been made to develop new technologies capable to produce functionalized surfaces. One of these technologies is the Direct Laser Interference Patterning (DLIP) technology, which permits to combine high fabrication speed with high resolution even in the sub-micrometer range. In DLIP, a laser beam is split into two or more coherent beams which are guided to interfere on the work piece surface. This causes modulated laser intensities over the component’s surface, enabling the direct fabrication of a periodic pattern based on selective laser ablation or melting. Depending on the angle between the laser beams and the wavelength of the laser, the pattern’s spatial period can be perfectly controlled. In this study, we introduce new modular DLIP optical heads, developed at the Fraunhofer IWS and the Technische Universität Dresden for high-speed surface laser patterning of polymers and metals. For the first time it is shown that effective patterning speeds of up to 0.7 m2/min and 0.4 m?/min are possible on polymer and metals, respectively. Line and dot-like surface architectures are shown with spatial periods between 5 µm and 22 µm are shown. The coefficient of friction of patterned steel under lubricated conditions is reduced by 25%.

9736-35, Session 8

Laser-assisted reduction of graphene oxide for paper based large area flexible electronics Enkeleda Balliu, Henrik Andersson, Magnus Engholm, Sven Forsberg, Håkan Olin, Mid Sweden Univ. (Sweden) Printed electronics is becoming more popular for fabrication of applications on flexible substrates. The substrates have mainly been plastics but the use of paper is becoming more widespread due to lower cost and recyclability. Consider also the possibility of using the very large area manufacturing techniques, today used in the paper making industry, for production of electronic applications. Manufacturing of conductive tracks at low cost is of

150

great importance for large area printed electronics. The materials commonly used is metals, carbon powder or conductive polymers in the form of inks. A more recent development is the use of graphene or Graphene Oxide (GO). GO is a poor conductor but after reduction the conductivity can increase several orders of magnitude. GO has a much lower cost than metal inks and if coated over large areas of the substrate, the parts that needs to be conductive can be selectively reduced. This makes laser assisted reduction of GO a promising and fast process method for fabrication of conductive tracks on large area paper based substrates. The GO was prepared on several different paper substrates and conductive tracks where fabricated by using and evaluating different laser sources coupled to a laser scanning mirror system. We will present our investigation showing promising results, but is highly dependent on several laser parameters as well as GO layer thickness and density. A reduction of sheet resistance from 3.5 MOhm for unreduced r-GO down to ~550 Ohm is obtained without any observable damage to the paper substrates.

9736-36, Session 8

Direct laser interference patterning for decreased bacterial attachment Denise Guenther, TU Dresden (Germany); Jaoine Valle, Saioa Burgui, Carmen Gil, Cristina Solano, Alejandro Toledo-Arana, Univ. Pública de Navarra (Spain); Ralf Helbig, Leibniz-Institut für Polymerforschung Dresdene e.V. (Germany); Carsten Werner, Leibniz Institute of Polymer Research Dresden (Germany); Inigo Lasa, Univ. Pública de Navarra (Spain); Andrés F. Lasagni, TU Dresden (Germany) In the past 15 years, many efforts were made to create functionalized articial surfaces showing special anti-bacterial and anti-biofouling properties. Thereby, the topography of medical relevant materials plays an important role. However, the targeted fabrication of promising surface structures like hole-, lamella- and pyramid-like patterns is still a challenge. Optical and e-beam lithography, mouling and self-assembly layers show a great potential to design topographies for this purpose. At the same time, most of these techniques are based on sequential processes, require masks or moulds and thus are very device relevant and time consuming. In this work, the Direct Laser Interference Patterning Technology (DLIP) as a sophisticated technology for the fast, flexible and direct creation of periodic micrometer- and submicrometer structures is presented. This method offers the possibility to equip large plain areas and curved devices with 1D, 2D and 3D patterns. Simple 1D (e.g. lines) and complex 3D (e.g. lamella, hierarchichal pillars) patterns with feature sizes from 300 nm to 5 µm were fabricated on polymeric materials (PS and PET). Subsequently, adhesion behavior of S. aureus and S. epidermidis bacteria was characterized under in-vitro and in-vivo conditions. The results revealed that the topographies in micrometer scale have a significant impact on bacterial adhesion. On the one hand, one-dimensional line-like structures especially with dimensions of the bacteria enhanced microbe attachement. While on the other hand, complex three-dimensional patterns prevented biofilm formation even after implantation and contamination in living organisms.

9736-37, Session 8

Precision laser processing of diamond with 3D resolution Patrick S. Salter, Yu-Chen Chen, Bangshan Sun, Jason M. Smith, Martin J. Booth, Univ. of Oxford (United Kingdom) We demonstrate the versatility of direct laser writing for restructuring diamond. An ultrashort pulsed beam is focused into diamond at high numerical aperture. The structural modifications resulting from multiphoton absorption at the focus are highly localised in three dimensions. The incident laser beam is shaped using adaptive optics to remove the severe aberrations

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9736: Laser-based Micro- and Nanoprocessing X induced at the diamond interface, such that accurate fabrication can be achieved over a large 3D volume. At higher pulse energies, the breakdown of the diamond lattice occurs at the laser focus to leave an amorphous carbon phase. The laser focus may be subsequently traced through the diamond to create continuous conductive wires. Adaptive optics aberration correction is essential for low resistivity wires which can follow three dimensional paths. These wires are showing great promise in diamond based sensors. We also introduce a new fabrication regime in diamond whereby reducing the pulse energy we are able to demonstrate the generation of nitrogen vacancy (NV) colour centres. With careful control over the incident pulse energy it is possible to gently perturb the diamond lattice with a single pulse to cause minimal structural disruption. Such modifications are not visible by conventional transmission microscopy, but can be seen in a confocal microscope mapping photoluminescence. Following a high temperature anneal, the laser modified sites exhibit spectroscopic properties strongly characteristic of NV- colour centres. Hanbury-Brown Twiss measurements provide a strong indication that the laser processing has resulted in single isolated NV- defects: atomic level restructuring with minimal surrounding damage.

9736-38, Session 9

Fluorine laser induced surface modification and micro/nanostructuring of metal thin films (Invited Paper) Masayuki Okoshi, National Defense Academy (Japan) and Kanto Gakuin Univ. (Japan) Nanoswellings of 60 nm height and 500 nm diameter on average of an iron thin film deposited on a silica glass substrate at regular intervals of 2.5 micron were fabricated by the irradiation of a 157 nm fluorine laser. The fluorine laser was focused on the iron thin film by each microsphere made of silica glass of 2.5 micron diameter, which covered the entire surface of the films. The surface of the silica glass substrate underneath the fluorine laser irradiated iron thin film selectively swelled to push up the film. After the laser induced micro/nanostructuring, the fluorine laser was again irradiated onto the entire surface of the periodic micro/nanostructured iron thin film to form an approximately 2 nm thick Fe3O4 modified layer. As a result, the samples showed hydrophobicity and high corrosion resistance to 3 wt% NaCl aqueous solution (quasi-seawater). No rust was observed on the samples after the immersion test in the quasi-seawater for 24 h.

9736-39, Session 9

CFRP bonding pre-treatment with laser radiation of 3µm wavelength: laser/ material interaction David Blass, Stefan Kreling, Technische Univ. Braunschweig (Germany); Sebastian Nyga, Thomas Westphalen, Bernd Jungbluth, Hans-Dieter Hoffman, Fraunhofer institute for laser technology (Germany); Klaus Dilger, Technische Univ. Braunschweig (Germany) The application of carbon fiber reinforced plastics in combination with adhesive bonding has a high potential for the mass reduction of structural automotive parts. Due to the mold based manufacturing process of the composite parts, surface contaminations (e.g. release agents residues) are inevitable. Therefore a surface pre-treatment prior to the bonding process is necessary. State of the art pre-treatment processes are mechanical treatments like manual abrading or grit blasting which increase the production time. As an alternative approach laser radiation offers the possibility for a sufficient (clean surfaces) and efficient (high process speeds) surface pre-treatment. Unfortunately the most common laser sources with their

Return to Contents

wavelengths between 350 and 1200 nm show a high transmission for the matrix resin, or in case of high absorption (10,6 µm) a thermal degradation of the polymer. Both effects lower the quality of the pre-treatment process. Contrary laser radiation with 3 µm wavelength has a high absorption in the matrix resin with a correlating optical penetration depth which is smaller than the thickness of the resin layer. In addition the thermal degradation is lower compared to CO2 laser radiation. This provides the opportunity for a sensitive laser-based surface pre-treatment. During this investigation the interactions of the 3 µm laser radiation with reinforced and non-reinforced epoxy are evaluated and compared with a classic fiber laser and an UV-laser. As well mechanical (e.g. ablation behavior) as chemical (matrix degradation) are considered. It could be shown, that the contaminations can be removed damage free with the new wavelength.

9736-40, Session 9

Picosecond laser welding of optical to metal components Richard M. Carter, Heriot-Watt Univ. (United Kingdom); Michael Troughton, Selex ES Ltd. (United Kingdom); Jianyong Chen, Heriot-Watt Univ. (United Kingdom); Ian F. Elder, Selex ES Ltd. (United Kingdom); Robert R. Thomson, Heriot-Watt Univ. (United Kingdom); Robert A. Lamb, Selex ES Ltd. (United Kingdom); M. J. Daniel Esser, Duncan P. Hand, Heriot-Watt Univ. (United Kingdom) We report on practical, industrially relevant, welding of optical components to aluminum alloy components. Weld formation is achieved through the tight focusing of a 5.9ps, 400kHz Trumpf laser operating at 1030nm. By selecting suitable surface preparation, clamping and laser parameters, the plasma can be confined, even with comparatively rough surfaces, by exploiting the melt properties of the glass. The short interaction time allows for a permanent weld to form between the two materials with heating limited to a region ~300 µm across. Practical application of these weld structures is typically limited due to the induced stress within the glass and, critically, the issues surrounding post-weld thermal expansion. We will comment on these issues, presenting measurements of the induced stress within the glass component and present a range of weld geometries and pre-welding surface preparations to minimise post-welding thermal issues. In addition we will report on both the mechanism of the weld formation and on the measured strength of the weld, with a particular emphasis on laser parameters and surface preparation. A measured weld strength at least one order of magnitude greater than equivalent adhesive bonding approaches will be presented.

9736-41, Session 9

Sapphire ablation by water jet guided 532nm ns-pulsed laser Yury Kuzminykh, Seyed Payam Vahdati, EMPA (Switzerland); Annika Richmann, Bernold Richerzhagen, Synova S.A. (Switzerland); Patrik W. Hoffmann, EMPA (Switzerland) Laser micro-machining of sapphire is a demanded technology, which is not yet perfectly mastered. In our contribution we investigate the ablation process of sapphire by a water jet guided frequency doubled Nd:YAG laser (532 nm) with the pulse length of ~100ns. The laser radiation is guided to the sample surface in a medium pressure (400 bar) laminar water jet of 30-50µm diameter by total internal reflection. This set-up allows efficient and high-quality scribing and cutting of sapphire plates of up to several mm thickness. We have investigated the details of the ablation process using a precisely triggered high speed camera with down to 100ns exposure

+1 360 676 3290 · [email protected]

151

Conference 9736: Laser-based Micro- and Nanoprocessing X time. We have imaged and recorded the dynamics of the ablation plume expansion. Lifetime of the ablation plume is found to be in the range of 400-500ns. The ablation threshold of the sapphire was found to be higher than for the ablation using comparable laser in air. The strong interaction of plasma plume with the water jet has been observed.

9736-44, Session 10

9736-42, Session 10

Christian Schindler, Ernst-Abbe-Hochschule Jena (Germany); Maria Friedrich, Günter-Köhler-Institut für Fügetechnik und Werkstoffprüfung GmbH (Germany); Jens Bliedtner, Ernst-Abbe-Hochschule Jena (Germany)

Photochemical reduction of graphene oxide (GO) by femtosecond laser irradiation Muttaqin Yasin, Takahiro Nakamura, Shunichi Sato, Tohoku Univ. (Japan) Graphene oxide (GO) has attracted much attention as a precursor of graphene. But, reduction process of GO is essential to obtain fascinating properties of graphene. Among many reduction methods, reduction of GO by laser irradiation is versatile method to reduce oxygen-based functional groups from GO and is applicable either in colloidal solution or in film form. In the present study, femtosecond laser pulses (?: 800 nm, pulse width: 100 fs, repetition rate: 300 Hz) were employed, and different parameters such as laser fluence and irradiation time were examined to obtain highly reduced graphene oxide (rGO). By applying different laser fluence with the constant irradiation time, GO solution had optically changed from yellowpale into black. The peak absorption in UV-vis. absorption spectrum shifted from 230 to 275 nm after 2 hours irradiation with the laser fluence of 80 mJ/cm2. Further increase in the irradiation time gave drawbacks result due to re-oxidation of rGO. It was also shown by FT-IR and X-ray photoelectron spectroscopy that oxygen functional groups were effectively reduced after laser irradiation. Additionally, intensity ratio of D and G bands in Raman spectrum of rGO decreased more than 15 % compared to that of GO which is quite different with the conventional chemical or thermal methods. This indicates that the enhancement of sp2 domains with maintaining the defect sites on GO through the reduction process. Moreover, the electronic conductivity of rGO significantly increased. This demonstrates a potential application of femtosecond laser in synthesize graphene based materials for specific purposes. (249 words)

9736-43, Session 10

Laser ablation of metal and semiconductors in arsenic sulfide solution Tingyi Gu, Princeton Univ. (United States); Burhan Abdi, Cornell Univ. (United States); Romain Fardel, Craig B. Arnold, Princeton Univ. (United States) Uniform dispersion of metallic and semiconductor nanoparticles in chalcogenide glass matrix is an effective way of modifying glass properties. Such materials could lead to important applications in active and passive photonic devices. It has previously been shown that sliver particles can be created uniformly in chalcogenide glass. In this work, laser ablation is applied to generate semiconductor particles in arsenic sulphide glass, including germanium or gallium. The chalcogenide glass with the laser assisted liquid phase synthesis is further examined by Raman and photoluminescence spectrum. We identify nanoparticle formation along with formation of semiconductor-sulfide bonds. Spin coated thin films of the nanoparticle doped chalcogenide solution reveal a uniform distribution of nanoparticles.

152

Analysis of process parameter for the ablation of optical glasses with femto- and picosecond laserpulses

Non-linear absorption through high intensities and a-thermal ablation allow micro material processing of optical glasses inducing only very low strain. These effects enable new process chains for photonics production fields with ultrashort pulsed laser radiation. We accomplished experiments with an ultrashort pulsed laser system emitting pulses ranging from 350 fs to 10 ps and a maximum average power of 50 W at 1030 nm. The laser beam gets deflected by a galvanometric scan-system with maximum scan speed of 2500 mm/s and focused by F-theta lenses onto the substrates. By design of experiments the influence of pulse energy, fluence and material conditions on the target figures is analysed. These are represented by the material characteristics mean squared roughness, ablation depths as well as the microcrack distribution in depth. The experimental procedure is applied onto a series of quartz glass, SF6 and phosphate glass samples. The findings give suggestions for process windows and display potential for process improvements.

9736-45, Session 11

Laser processing of compound semiconductor thin film photovoltaics (Invited Paper) Michael A. Scarpulla, The Univ. of Utah (United States) Laser recrystallization of thin film silicon and transparent conducting materials over the entire area is enabling technology for nearly all flat panel displays, including those at the >1 m2 area scale matching solar modules. The challenges in materials and laser sources are severe when trying to extend these techniques to compound semiconductors such as CdTe and Cu(In,Ga)Se2 (CIGSe). Stoichiometry control is especially critical and challenging for compound semiconductors, which severely restricts the possibilities for liquid phase processing as used for Si. In this talk, the opportunities and restrictions for laser processing in CIGSe and CdTe thin film photovoltaic technologies will be discussed. Process windows for CW and ns pulsed lasers are outlined for processes of crystallization and phase formation as well as for surface modification for contacting and surface passivation. These themes will be illustrated primarily in the context of CdTe but results from CIGSe will also be presented.

9736-46, Session 11

Laser direct interference patterning and ultrafast laser-induced micro/nano structuring of current collectors for lithium-ion batteries Yijing Zheng, Karlsruhe Institute of Technology (United States); Johannes Pröll, Karlsruhe Institute of Technology (Germany); Tim Kunze, Fraunhofer IWS Dresden (Germany); Andrés-Fabián Lasagni, Fraunhofer IWS Dresden (Germany) and TU Dresden (Germany); Christian Brösicke, Karlsruhe Institute of Technology (Germany); Peter Smyrek, Karlsruhe Institute of Technology (Germany)

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9736: Laser-based Micro- and Nanoprocessing X and Karlsruhe Nano Micro Facility (Germany); Hans J. Seifert, Wilhelm Pfleging, Karlsruhe Institute of Technology (Germany) Laser-assisted modification of metals, polymers or ceramics yields a precise adjustment of wettability, biocompatibility or tribological properties for a broad range of applications. Due to a specific change of surface chemistry and/or surface topography on micro- and nano-meter scale, new functional properties can be achieved. A rather new scientific and technical approach is the laser-assisted surface modification and structuring of metallic current collector foils for lithium-ion batteries. Prior to the thick film electrode coating processes, the formation of micro/nano-scaled surface topographies on current collectors is critical with respect to an improvement in film adhesion, mechanical anchoring, and electrical contact. These features in turn impact on the battery performance and the battery life-time. The volume change during de-/insertion of lithium-ions is crucial for future high power silicon-based anode materials. Volume changes can reach values up to 400% causing delamination of the active material from the current collector leading to dramatic capacity loss after few cycles.

extended cycle and calendar life-time. For this purpose, prediction and estimation of battery life-time and degradation mechanisms are of great interest. Previous studies have shown that laser-structuring of threedimensional (3D) micro-pillars in cathode thick films increases the active skin surface and therefore the lithium-ion diffusion kinetics. Within this study, NMC thick films were prepared by tape-casting and subsequent ultrafast laser-structuring. The lithium distribution in electrochemically cycled and unstructured / fs laser-structured NMC cathodes was investigated post-mortem by using Laser-Induced Breakdown Spectroscopy (LIBS). The main goal is to develop an optimized three dimensional cell design with improved electrochemical properties based on studies of the homogeneity of the local State-of-Charge. LIBS experiments were carried out using a LIBS workstation (type: FiberLIBS SN013, Secopta GmbH, Germany) equipped with a mode-locked DPPS Nd:YAG laser operating at a wavelength of 1063nm. The element distribution was investigated using two different techniques: element mapping and element depth-profiling of the unstructured / fs laser-structured electrode surface. Results achieved from post-mortem studies using LIBS will be presented.

In order to enhance the adhesion of thick film anode materials, the formation of 3D surface architectures on copper current collectors is investigated by applying two advanced laser processing structuring technologies: laser direct interference patterning (DLIP) and ultrafast laserinduced periodic surface structuring.

9736-48, Session 11

The formation of laser-induced periodic surface structures (LIPSS) on metallic surfaces was investigated as function of laser parameters such as wavelength, scanning speed, pulse number, and laser fluence. Well defined LIPSS with periodicities from 200 nm up to 440 nm could be generated. Hierarchical structures combined with LIPSS were fabricated by using appropriate laser parameters. Also, hydrophobic properties with water contact angles of about 145° could be measured.

Jinguang Cai, Akira Watanabe, Tohoku Univ. (Japan)

With respect to the direct laser interference patterning (DLIP) of current collector foils, a laser beam with ns or ps pulse lengths was split into several collimated and coherent laser beams and finally superimposed on the metallic surface. By adjustment of the processing parameters, line structures with periodicity from 1.3 µm up to 10 µm were formed on surfaces. After laser structuring via LIPSS or DLIP, silicon-based as well as graphitebased composite materials were deposited by tape-casting on the modified current collectors. The electrode film adhesion was characterized by tensile strength measurements and the electrochemical performance was measured within cycling of battery test cells.

9736-47, Session 11

Post-mortem characterization of fs laser-generated micro-pillars in Li(Ni1/3Mn1/3Co1/3)O2 electrodes by laser-induced breakdown spectroscopy Peter Smyrek, Johannes Pröll, Karlsruhe Institute of Technology (Germany) and Karlsruhe Nano Micro Facility (Germany); Hans J. Seifert, Karlsruhe Institute of Technology (Germany); Wilhelm Pfleging, Karlsruhe Institute of Technology (Germany) and Karlsruhe Nano Micro Facility (Germany) The development of new active materials, electrode architectures and innovative manufacturing strategies for lithium-ion batteries is quite important in order to optimize battery performance and production cost. In recent years, strong efforts have been undertaken to study physical and chemical properties of cathode materials which develop towards the direction of high energy density, high power density, long cycle life and environment friendly. Lithium nickel manganese cobalt oxide (NMC) has been reported as one of the promising cathode material because of its many advantages such as high rate capability and good thermal stability. Nevertheless, for automotive applications lithium-ion batteries require

Return to Contents

Flexible carbon micro-supercapacitors prepared by laser direct writing Recently, the rapid development of miniaturized portable electronic devices has greatly motivated the study on micro-/nano-scale power supply units with high energy and high power densities. Supercapacitors have been widely studied over the past few years due to their high power density, robust cycle performance, pollution-free operation, and maintenance-free features. Besides, supercapacitors with small size, light weight, flexibility while maintaining high energy and power output are required for portable miniaturized electronics. In-plane micro-supercapacitors (MSCs) are recognized as the potential power supply units in portable devices, due to their simplified packaging processes and compatibility to the integrated circuits. However, the fabrication methods and materials should be costeffective, scalable, and compatible to current electronic industry. Carbon materials own high specific surface areas, electrochemical stability, and high electrical conductivity, which are critical parameters for high-power supercapacitors. Moreover, the high mechanical tolerance makes them good candidates for flexible wearable devices. Therefore, MSCs based on carbon materials would satisfy the requirements of portable electronics. In this work, we demonstrated the fabrication of flexible carbon MSCs by laser direct writing on commercial polyimide sheets with very cheap CW laser diode. The structures and compositions of obtained carbon materials are detailedly characterized as pore structures, which may be in favor for the immersion of electrolyte. As-prepared micro-supercapacitors show a high capacitance of about 9 mF/cm2 at a scanning rate of 10mV/s, which is comparable to the reported highest capacitance of carbon-based supercapacitors fabricated by pulse-laser writing. In addition, the flexible micro-supercapacitors have high bend tolerance and long-cycle stability.

9736-49, Session 11

High speed, high quality Li-ion battery foil cutting using nanosecond lasers Jim M. Bovatsek, Rajesh S. Patel, Robert S. Sposili, Spectra-Physics (United States); Rukun Yang, Xueke Wu, Shenzhen Geesun Automation Technology Co., Ltd. (China) Pulsed infrared (IR) lasers have, in many cases, successfully replaced mechanical punching processes for Li-ion battery foil cutting. While the lower cost of IR pulsed lasers is attractive to manufacturers, IR laser process has its limitations. It can leave a large heat affected zone on the tab material and a sharp burr attached to the cut edge. These can potentially be a safety

+1 360 676 3290 · [email protected]

153

Conference 9736: Laser-based Micro- and Nanoprocessing X hazard for batteries during their life cycle. Past studies have shown that using green or ultraviolet (UV) lasers, smaller kerf width and better edge quality can be achieved. However, the cutting speed achieved was low and not acceptable to battery manufacturers due to the lower power of green and UV lasers. With recent advances in laser technology, we at SpectraPhysics® have developed cost effective high power, high repetition rate green and UV lasers that can solve the cutting speed problem. In this paper, we present Li-ion battery foil cutting results achieved using our high power nanosecond Quasar® hybrid fiber laser with pulse-shaping technology. The results show speeds of 1 m/s or higher can be achieved with a burr size of 10 um or less for cutting current-carrying conductors, anode, and cathode foils.

154

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9737: Synthesis and Photonics of Nanoscale Materials XIII Monday - Wednesday 15–17 February 2016 Part of Proceedings of SPIE Vol. 9737 Synthesis and Photonics of Nanoscale Materials XIII

9737-1, Session 1

Biocompatible gold submicrometer spheres with controlled surface textures fabricated by pulsed laser melting in liquids Christoph Rehbock, Alexander Heinemann, Janina Zwartscholten, Stephan Barcikowski, Univ. Duisburg-Essen (Germany) Gold Submicrometer spheres (Au-SMS) are applicable in optics due to their well-defined uniform shape combined with a very high scattering cross section. As synthesis of these nanostructures via chemical synthesis proofs to be difficult, the process of Pulsed Laser Melting in Liquids (PLML) has been well established to synthesize SMS from a broad range of materials using aggregated source nanoparticles [1,2]. In this work we used the totally biocompatible additive NaCl to induce aggregation of laser-generated gold nanoparticles, while in a consecutive step we performed reirradiation with a ns-laser (?=532 nm). We could confirm the formation of Au-SMS, size controlled in a regime of 200-400 nm by laser fluence. Interestingly, we found that along with increasing average fluence the portion of wrinkled surface textures became more abundant. This is most likely due to the partial onset of fragmentation processes and deposition of small particles on the SMS. Additionally, we could show that the surface texture of the SMS critically depends on the size distribution of the educt material [3]. These strategies could give access to SMS with tailor-made surface structures e.g. for SERS-applications. References: [1] A. Pyatenko, H. Wang, N. Koshizaki, T. Tsuji, Laser & Photonics Reviews, 1-9 (2013) [2] T. Tsuji, T. Yahata, M. Yasutomo, K. Igawa, M. Tsuji, Y. Ishikawa, N. Koshizaki, Physical Chemistry Chemical Physics, 3099–3107 (2013). [3] C. Rehbock, J. Zwartscholten and S. Barcikowski, Chem. Lett., 2014, 43, 1502-1504.

9737-2, Session 1

Direct laser fabrication of nanowires on semiconductor surfaces Haeyeon Yang, Anahita Haghizadeh, South Dakota School of Mines and Technology (United States) Lateral semiconductor nanowires are typically fabricated by the selfassembly process that is driven by the strain-relaxation mechanism. However, the nanowire dimensions – width, height, and length – are difficult to control. We have observed semiconductor nanowires from the surfaces when they are irradiated by high power laser pulses interferentially. The narrowest nanowires observed have the width smaller than 20 nm from GaAs surfaces, which is more than 10 times smaller than the interference period while the smallest width of nanowires from the Si(001) surface is about 50 nm, which is larger than that from GaAs but still more than four times smaller than the interference period used. Furthermore, the dimensions depend on the interferential parameters such as intensity and interference period. These nanowires form when the top surface atoms are selectively mobilized by transient thermal gratings, which are created on the surface by the interferential irradiation of high power laser pulses. We study impacts of the transient thermal grating on morphologies of nanowires on semiconductor surfaces. Strain-free, self-assembled nanodots as well as periodic nanowires are observed from Si and GaAs(001) surfaces when

Return to Contents

the surfaces are irradiated interferentially by high power laser pulses. The morphologies of the nanostructures are studied by atomic force microscopy. The period of the grating is varied by varying the laser wavelengths used as well as the interference angle. The nanowires are usually produced by a single application of laser interference but also observed from the surfaces irradiated by a few times.

9737-3, Session 1

Modeling nanoparticle formation by laser ablation and by plasma discharges (Invited Paper) Tatiana E. Itina, Andrey Voloshko, Lab. Hubert Curien (France) Nanoparticles have found numerous applications in such areas as photonics, electronics, medicine, etc. Further development of these fields requires reliable and versatile methods of nanoparticle synthesis with well-controlled properties. Among promising synthesis techniques, both laser ablation and plasma discharges are considered. These methods provide numerous advantages that are unique in several cases. On one hand, the main advantage of the laser ablation method is in the possibilities of changing laser parameters and background conditions and in its capacity to preserve stoichiometry. Laser-based methods also yield bio-compatible nanoparticles and nano-colloids with unique chemical properties. Laser-induced fragmentation provides additional control ways over nanoparticle sizes. In addition, doubled and shaped laser pulses can be applied for a better control over nanoparticle sizes. On the other hand, the major advantage of plasma discharge technique is in the possibility of using several facilities in parallel to increase the yield of nanoparticles. Spark-based methods allow formation of very small nanoparticles in gas-phase, whereas much larger nanoparticles can be formed by using arc discharges. To better understand and to optimize these processes, detailed numerical modeling is performed. The involved stages are considered and analyzed. The resulting nanoparticle parameters are investigated as a function of the experimental conditions. Nanoparticle properties, such as mean size and mean concentration are analyzed. Differences and similarities between the considered synthesis methods are discussed. Optimal experimental conditions are furthermore suggested based on the resulted nanoparticle characteristics in agreement with several previous experiments.

9737-4, Session 1

Laser-assisted synthesis and manipulation of two-dimensional layered semiconductors (Invited Paper) Masoud Mahjouri-Samani, Oak Ridge National Lab. (United States); Mengkun Tian, The Univ. of Tennessee Knoxville (United States); Ming Wei Ling, Andrew R. Lupini, Kai Wang, Christopher M. Rouleau, Alexander A. Puretzky, Gyula Eres, Ilia N. Ivanov, Kai Xiao, Oak Ridge National Lab. (United States); Gerd Duscher, The Univ. of Tennessee Knoxville (United States); David B. Geohegan, Oak Ridge National Lab. (United States) Two-dimensional layered semiconducting materials, particularly the metal chalcogenides, have recently attracted significant renewed attention due to the novel physical, chemical, electrical and optical properties.

+1 360 676 3290 · [email protected]

155

Conference 9737: Synthesis and Photonics of Nanoscale Materials XIII Developing new methods for controlled synthesis and manipulation of these layered materials is crucial for emerging applications in functional devices. Here we demonstrate the use of pulsed laser vaporization as a versatile method for the synthesis and processing of 2D layered semiconductors with controlled number of layers, crystallite size, growth location and composition. This PLV approach offers a new synthesis solution to address the challenges of conventional vapor phase growth methods (e.g., CVD), by taking advantage of tunable kinetic energy of the lasergenerated precursors for formation of either atomic species in vacuum, or stoichiometric nanoparticles in background gases for the synthesis of various 2D layered materials. Utilizing the stoichiometric nanoparticles as feedstocks, we demonstrate the formation of either small domain nanosheet networks (~ 200 nm) or large crystalline domains (~100 µm). High kinetic energy atomic species, on the other hand, are used in doping, alloying and formation of lateral heterojunction within monolayer 2D crystals. The synthesis and conversion processes are further studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy, as well as by fabrication and characterization of simple optoelectronic devices. These novel laser-based synthesis and processing approaches enable the controlled synthesis and manipulation of 2D layered semiconductors for ultrathin optoelectronics and devices. Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facility Div. (characterization science).

9737-5, Session 2

Modeling of laser-assisted nanostructuring of materials (Invited Paper) Irina N. Zavestovskaya, P.N. Lebedev Physical Institute (Russian Federation) No Abstract Available

9737-6, Session 2

Large area, homogeneous laser-inducedperiodic-surface-structures (LIPSS) produced by high repetition rate, fs-laser beam scanning at high speed Daniel Puerto, Jan Siegel, Instituto de Óptica “Daza de Valdés” (Spain); Ruth Lahoz, Instituto de Ciencia de Materiales de Aragón (Spain); Javier Hernandez-Rueda, Univ. of California, Davis (United States); Alexandro Ruiz de la Cruz, Instituto de Óptica “Daza de Valdés” (Spain); Xerman F. de la Fuente, Instituto de Ciencia de Materiales de Aragón (Spain); Javier Solis, Instituto de Óptica “Daza de Valdés” (Spain) The formation of Laser-Induced Periodic Surface Structures (LIPSS) is a universal phenomenon that has been observed in a wide variety of materials. It is generally accepted that LIPSS formation relates to the interference of the incident beam with a surface wave (scattered or induced) in a process greatly conditioned by the transient complex refractive index of the strongly excited material. In metals, electron-phonon coupling, plasma density and electron diffusion have been identified as important parameters for LIPSS formation at low fs-laser repetition rates. In this work we report on the unique characteristics of low spatial frequency LIPSS in Cr and other materials upon high repetition rate, fs-laser beam scanning irradiation. Highly regular, large area patterns with sub-wavelength period can be produced for a wide range of repetition rates (100´s kHz range), over large areas (~cm^2) and high scan speeds (~m/s). Different irradiation conditions (laser repetition rate, wavelength, beam polarization,

156

pulse energy, scan speed and scan line separation) have been explored with view on the possible influence of thermal accumulation and geometrical factors on the homogeneous propagation of the sub-wavelength structure over macroscopic regions. The best results in terms of modulation amplitude and homogeneous extension of the LIPSS orientation are observed for the scanning direction perpendicular to the polarization axis. Optimal, large area (~10 cm^2) surface structures in Cr can be produced in a few minutes showing relative diffraction efficiencies up to ~40%. The processing strategy is robust in terms of broad parameter windows and applicable to other materials.

9737-7, Session 2

Ejection of glass melts and generation of nanofibers from the back surface of a glass plate by pulsed UV laser irradiation Sho Itoh, Nippon Electric Glass Co., Ltd. (Japan) and Kyoto Univ. (Japan); Masaaki Sakakura, Yasuhiko Shimotsuma, Kiyotaka Miura, Kyoto Univ. (Japan) Several applications of glass nanofibers have been proposed for the past years. We found a method for fabricating nanofibers with a diameter of 100 nm order from thin glass substrates using a nanosecond pulsed UV 355 nm laser. In the latest report, we studied the generation process of nanofibers, which showed that voids were formed in the substrate during laser irradiation, and then materials seemed to be pushed from the back surface. However, the details of the generation mechanism have not become clear. Here, we focused on the behavior of ejection of the material, and investigated the reason for nanofiber generation. According to the high-speed camera images taken by synchronizing to the laser oscillator, we confirmed that molten glass was ejected from the back surface of substrates. To simplify the process, we conducted irradiation to substrates without scanning the laser beam. As a result, when focusing location was set below the back surface, glass was cracked, caused by heat generated around the irradiated area along with drilling. Thus, we considered that nanofibers were generated from the ejected molten glass, which was caused by heating and drilling through the molten part of substrates by the pulsed laser. We will also present a possible mechanism for the driving force of pushing the molten part from glass substrate. Understanding the mechanism leads to the process control of glass nanofiber fabrication.

9737-8, Session 2

Effects of laser parameters on size and dispersion of gold nanoparticle colloids formed by laser ablation in water Alexandr A. Antipov, Sergey M. Arakelyan, Vladimir State Univ. (Russian Federation); Yury V. Ryabchikov, Ahmed Al-Kattan, Andrei V. Kabashin, Aix-Marseille Univ. (France) and Lasers, Plasmas et Procédés Photoniques (France); Stella V. Kutrovskaya, Alexey O. Kucherik, Vladimir State Univ. (Russian Federation); Tatiana E. Itina, Lab. Hubert Curien (France) Gold nanoparticles (Au NPs) attract particular attention because of their unique size-dependent chemical, physicochemical and optical properties [1-2] and, hence, their potential applications in catalysis, nanoelectronics, photovoltaics and medicine. In particular, laser-produced colloidal nanoparticles [2-3] are known to be not only bio-compatible, but also reveal unique chemical properties. In addition, different laser systems can be used for synthesis of these colloids, varying from continuous wave (CW) to ultra-short femtosecond lasers. However, despite rapidly growing interest in laser-based synthesis techniques, the choice of laser system is still not clear enough for concrete applications. To bring more light at this issue,

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9737: Synthesis and Photonics of Nanoscale Materials XIII we investigate an influence of laser parameters on a gold target immersed in deionized water. First, diagnostics of CW laser-induced hydrodynamic processes close to gold surface is performed. It is shown that gas bubbles do not form during continuous laser heating. Gold nanoparticle colloids with average size 7–8 nm and narrow size distribution (3–5 nm) owing to CW laser ablation are formed. The obtained results are compared with the ones obtained by using the second harmonics and with previous results obtained by using femtosecond laser systems. [1] Mafuné F, Kohno J Y, Takeda Y and Kondow T 2000 J. Phys. Chem. B 106 7575–7577 [2] Maximova K, Aristov A and Kabashin A V 2015 Nanotechnol. 26 065601 [3] Sylvestre J P, Kabashin A V, Sacher E and Meunier M M 2005 Appl. Phys. A 80 753–758 ISSN 0947-8396

9737-9, Session 2

Laser synthesis of ultrapure nanomaterials for cancer theranostics Andrei V. Kabashin, Lasers, Plasmas et Procédés Photoniques (France) No Abstract Available

electrons (plasmons), nanoplasmonics offers two modalities for biosensing: (i) optical transduction, which detects changes in the refractive index of a dielectric medium adjacent to a gold nanostructure resulting from a binding event between a target analyte (antigens, DNAs etc.) and its corresponding receptor (antibodies etc.); (ii) Surface Enhanced Raman Scattering (SERS), which employs the effect of electric field enhancement near noble metal nanostructures to drastically enhance Raman scattering and thus detect trace amounts of biomaterials. A huge upgrade of current state-of-the-art plasmonic biosensing technology is now expected from the employment of novel sensing-oriented plasmonic metamaterials, or artificial materials composed of noble metal nanoblocks with nanoscale distance between them, which could provide new sensing principles/properties in order to radically improve sensing response [1,2] This presentation will describe metamaterial architectures, which can combine ultrasensitive optical biosensing with SERS-based recognition functionality. Such metamaterials are based on gold nanodot-based dimers arranged in a periodic lattice. We show that such structures can provide extremely high phase sensitivity to refractive index variations due to the excitation of localized plasmon resonances [2]. On the other hand, a strong enhancement of electric field between nanodot dimer structures makes possible the implementation of parallel Surface Enhanced Raman Scattering and Surface Enhanced Fluorescence channels. By modifying Aperture-less SNOM technique based on a standard Ntegra Spectra system (NT-MDT), we map evanescent plasmonic field distribution near golden nanoparticles and in the gaps between the nanoparticles (hot spots) in order to optimize nanoarchitectures for hybrid sensing platforms. [1] Kabashin, A. V. et al. Nature Mater., 2009, 8, 867-871

9737-10, Session 3

[2] Kravets, V. G. et al. Nature Mater. 2013, 12, 304-309

Graphene plasmonics: Hybrid graphenewaveguide modulators (Keynote Presentation) Sasha Grigorenko, The Univ. of Manchester (United Kingdom) We discuss creation and operation of hybrid graphene-plasmonic waveguide modulators in which graphene is used to achieve on-chip processing of information. We consider several promising hybrid configurations, debate the importance of mode field configuration and geometry of waveguides for achieving high modulation depth and identify the most promising hybrid devices for telecom applications. Various working graphene-plasmonic modulators will be presented and compared with state-or-the art silicon modulators. Our proof-of-concept results pave the way towards on-chip realization of efficient graphene-based active plasmonic waveguide devices for optical communications.

9737-11, Session 3

Quantum-dot based ultrafast photoconductive antennae for efficient THz radiation (Invited Paper) Edik U. Rafailov, Aston Univ. (United Kingdom) No Abstract Available

9737-12, Session 3

9737-13, Session 3

Electrically biased GaAs/AlGaAs heterostructures for enhanced detection of bacteria Mohammad Reza Aziziyan, Jan J. Dubowski, Univ. de Sherbrooke (Canada) Nowadays, research focused on the development of rapid and low cost biosensing platforms is vastly increasing in response to the demand of numerous consecutive tests in the health sector. Different transducers have been investigated for detection of bacteria in aqueous solutions, addressing the need of controlling the level of bacteria in water, where large number of repeated tests is necessary. In that respect, biosensing based on photoluminescence of GaAs/AlGaAs heterostructures has been studied due to the promise of being a precise, fast and low cost diagnostic tool. However, bacteria adhesion studies have shown that electrical double layer repulsion of transducer surface can drive back bacteria immobilization process, resulting in restricted detection limit. We have investigated this effect using a 3-electrode fluidic setup, and applied potential measured against Ag/AgCl reference electrode. We demonstrate that electrically biased GaAs/AlGaAs heterostructures experience modulation of their band bending, which can lower this repulsion and result in improved bacteria immobilization. Changing band bending through electrical bias can vary the space charge region and alter conditions of a semiconductor interacting with electrically charged molecules. Whenever band bending is lowered the surface charge will decrease and so the double layer repulsion force. Hence, more amount of bacteria could approach the surface of GaAs and attach to it. Our results have shown that applying a 20 mV bias can double the surface coverage with bacteria.

Development of metamaterials for combined optical transduction/SERS biosensing/imaging platforms Artem Danilov, Aix-Marseille Univ. (France) Based on the unique property of noble metals to support oscillations of free

Return to Contents

+1 360 676 3290 · [email protected]

157

Conference 9737: Synthesis and Photonics of Nanoscale Materials XIII

9737-14, Session 3

9737-17, Session 4

Structural and nonlinear optical properties of gold-silicon nanoparticles formed in water by laser ablation at different fluences

Zinc oxide nanowire gamma ray detector with high spatiotemporal resolution

Yury V. Ryabchikov, Aix-Marseille Univ. (France) and P.N. Lebedev Physical Institute (Russian Federation); Anton Popov, Aix-Marseille University (AMU) (France); Ronan Le Dantec, Savoie University, SYMME Laborotary, 7 chemin de Bellevue, 74940 Annecy-le-Vieux, France (France); Vladimir Lysenko, Institut des Nanotechnologies de Lyon (France); Victor Y. Timoshenko, Lomonosov Moscow State Univ. (Russian Federation); Andrei V. Kabashin, AixMarseille Univ. (France) A technique of femtosecond laser ablation and fragmentation in pure deionized water was used to synthesize hybrid semiconductor-metal nanoparticles (Au-Si, Au-C etc). Depending on conditions of laserablative synthesis, the nanostructures had different nano-architectures such as hybrid aggregates or core-shells. Such hybrid structures could exhibit interesting optical properties, including enhanced absorption and photoluminescence. Based on excellent biocompatibility of constituents, the nanostructures present a novel, extremely promising object for biological imaging and therapy.

9737-15, Session 4

Brillouin microspectroscopy of nanostructured biomaterials: Photonics assisted tailoring mechanical properties (Invited Paper) Vladislav V. Yakovlev, Texas A&M Univ. (United States) No Abstract Available

9737-16, Session 4

Trions photogeneration in tungsten disulfide monolayers Abdelaziz Boulesbaa, Bing Huang, Kai Wang, Ming-Wei Lin, Masoud Mahjouri-Samani, Christopher M. Rouleau, Kai Xiao, Mina Yoon, Bobby G. Sumpter, Alexander A. Puretzky, David B. Geohegan, Oak Ridge National Lab. (United States) Recently, trions emerged as new three-body quasiparticles in atomically thin two dimensional (2D) materials. Here, we present the observation of two distinct negative trions T1 and T2 in tungsten disulfide monolayers (2D-WS2) on a sapphire substrate. Ultrafast pump-probe spectroscopy measurements indicated that two band-edge excitons, XA and XB, generated by the pump laser dissociated through hole trapping by the substrate, defects, or adsorbates, which rendered the material n-doped and resulted in new trionic transitions. Upon absorption of the probe laser photons, the generated electron-hole pairs joined the photo-doped electrons to form T1 and T2. Pumping with different photon energies followed by femtosecond white-light continuum probe revealed two different induced absorption peaks that can be assigned to two different trions, T1 and T2. The possible mechanism of this trion formation will be discussed. This finding highlights the important role of defects and substrates in defining optical and electrical properties of 2D metal chalcogenides.

158

Daniel C. Mayo, Vanderbilt Univ. (United States); Ryan Nolen, Lipscomb Univ. (United States); Andrew Cook, Richard Mu, Fisk Univ. (United States); Richard F. Haglund Jr., Vanderbilt Univ. (United States) Conventional scintillation detectors are single crystals of heavy-metal oxides or halides doped with rare-earth ions that report the recombination of electron-hole pairs by photon emission in the visible to ultraviolet. However, the light yields are typically low enough to require photomultiplier detection with the attendant instrumental complications. Here we report the first studies of gamma ray detection by large-area arrays of zinc oxide nanowires, grown by vapor-solid deposition. The nanowires grow along the c-axis in a wurtzite structure; they are typically 100 nm in diameter and have lengths of 1-2 µm. The nanowires are single crystals of high quality, with a photoluminescence (PL) yield from band-edge exciton emission in the ultraviolet that is typically one hundred times larger than the PL yield from defect centers in the visible. Nanowire ensembles were irradiated by 662 keV gamma rays from a Cs-137 source for up to ten hours; gamma rays in this energy range interact by Compton scattering, which in ZnO creates F+ centers that relax to form singly-charged positive oxygen vacancies. Following irradiation, we fit the PL spectra of the visible emission with a sum of Gaussians at the energies of the known defects. Over a period of days, the singly charged O vacancies relax to the more stable doubly charged O vacancies. However, the overall defect PL returns to pre-irradiation values after about a week, as the vacancies diffuse to the surface of these very thin nanowires, thus indicating that a self-annealing process restores the nanowires to their original state.

9737-18, Session 4

Ultra-low frequency Raman spectroscopy of two-dimensional MoSe2 crystals with arbitrary stacking configurations Alexander A. Puretzky, Liangbo Liang, Xufan Li, Kai Xiao, Kai Wang, Masoud Mahjouri-Samani, Oak Ridge National Lab. (United States); Leonardo Basile, Escuela Politécnica Nacional (Ecuador); Juan Carlos Idrobo, Bobby G. Sumpter, Oak Ridge National Lab. (United States); Vincent Meunier, Rensselaer Polytechnic Institute (United States); David B. Geohegan, Oak Ridge National Lab. (United States) Stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Here we report measurements and ab initio calculations of low frequency Raman shear and breathing modes in few layer MoSe2 synthesized by chemical vapor deposition with a variety of natural layer stackings and also stamped together with an arbitrary twist angle. We showed that the low frequency (LF) Raman modes (< 50 cm-1) that originate from interlayer vibrations can serve as ‘fingerprints’ to characterize not only the number of layers, but also their stacking configurations. Moreover, we showed how the low frequency shear and breathing modes evolve in twisted two-layer (2L) MoSe2 depending on the twist angle. The observed Raman spectra and their dependence on stacking configurations were interpreted using ab initio calculations of the frequencies and intensities. The low frequency modes in TMDs provide a powerful tool for understanding interlayer interactions and designing heterostuctures based on stacking of different TMD layers. Synthesis science was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. Characterization and computational science at CNMS was supported by the Scientific User Facilities Division, BES.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9737: Synthesis and Photonics of Nanoscale Materials XIII

9737-19, Session 5

9737-21, Session 6

High density semiconductor nanodots by direct laser fabrication

Pulsed laser deposition of ultrasmall nanoparticles: Transformation into photosensitive black-TiO2 core-shell nanostructures

Haeyeon Yang, Anahita Haghizadeh, South Dakota School of Mines and Technology (United States) Epitaxial nanodots are typically fabricated by the so-called StranskiKrastanov growth technique, which is an energy minimization process driven by the relaxation of accumulated strain energy. This process can results in high density quantum dots for energy related devices such as intermediate band solar cells because it is crucial to have high density nanodots for this and other optoelectronic device applications. However, large cluster defects begin to show up as the dot density is increased over the certain value, a critical density of about 7x1010 dots/cm2, over which the increase in dot density does not increase the performance of solar cells. We report a higher dot density than the critical value without formation of large clusters. These dots are observed from the GaAs(001) surfaces when they are irradiated interferentially by high power laser pulses of 7 ns. The laser wavelength used are 532, 355, and 266 nm. The dot density and morphology depend on the laser intensity and interference parameters such as wavelength and interference angle. The morphology of dots are examined by atomic force microscopy while their stoichiometry is characterized by energy dispersive electron spectroscopy in a field effect scanning electron microscope. The chemical analysis suggests that quality nanodots can be fabricated by irradiation of high power laser pulses on surfaces. Furthermore, these dots are strain-free so that the strain is not necessary anymore to fabricate quality nanodots.

9737-20, Session 6

Femtosecond laser irradiation of dielectric materials containing randomly-arranged nanoparticles Anton Rudenko, Jean-Philippe Colombier, Tatiana E. Itina, Lab. Hubert Curien (France) We investigate femtosecond laser irradiation of dielectric materials containing randomly distributed nano-defects. For this, numerical modeling is performed based on a solution of Maxwell equations together with kinetic equations for free electron excitation/relaxation processes. The processes of electron plasma generation due to both multiphoton and avalanche ionization are studied in fused silica in the presence of nanoparticles and/or nano-holes. In particular, light propagation is analyzed as a function of the defect size and density. The performed calculations show that the generated free electron plasma significantly depends of the defect density and on laser wavelength. The resulted distribution of the electromagnetic field and the following thermo-mechanical effects are examined and compared with the available experimental findings. The study can help in the evaluation of the damage threshold of such materials and allow a better control over laser nanomachining. Recent results have furthermore shed light on such effects as femtosecond laser-assisted volume nanograting formation previously observed in several dielectric materials [1,2]. The periodicity and the quality of the produced nanoplanes are found to strongly depend on the concentration of the initial defects and on the irradiation wavelength.

David B. Geohegan, Masoud Mahjouri-Samani, Oak Ridge National Lab. (United States); Mengkun Tian, The Univ. of Tennessee (United States); Gerd Duscher, The Univ. of Tennessee Knoxville (United States); Gyula Eres, Alexander A. Puretzky, Christopher M. Rouleau, Mina Yoon, Oak Ridge National Lab. (United States) The formation, pulsed laser deposition (PLD), and transformation of ultrasmall amorphous TiO2 nanoparticles into photosensitive core-shell TiO2/Ti2O3 crystalline nanoparticles (“black TiO2”) is reported. First, timeresolved in situ plume diagnostics are used to understand the conditions for the PLD of films consisting of pure, ultrasmall nanoparticles (UNPs, ~ 3 nm) in mesoporous architectures by laser ablation of TiO2 targets and condensation in low-pressure background gases. We describe an interesting regime where nanoparticles formed within the decelerating plasma plume propagate past it – answering a longstanding question in PLD. Second, these ultrasmall, amorphous TiO2 nanoparticles are then investigated as tunable “building blocks” for catalyst-free transformation into larger nanostructures or films with metastable crystalline phases. With increasing substrate temperature the UNPs are shown to integrate into nanowires, nanosheets, or vertically-oriented crystalline nanorods, sometimes with unusual metastable phases (e.g., TiO2(B), and “black TiO2”). Theory and simulation, along with state-of-the-art atomic-resolution Z-contrast scanning transmission electron microscopy, nano-beam electron diffraction (NBED), and electron energy loss spectroscopy (EELS), indicate that the evolution of a particular crystalline phase and preferred growth orientation is linked to the defects and ordering of TiO6 octahedral units within each metastable amorphous nanoparticle. We focus on the formation of “black TiO2”, a remarkable variant of TiO2 relevant to hydrogen production by photocatalytic water splitting. We discuss the generality of the technique to the formation of a variety of phases and nanostructure morphologies (of various materials) by alteration of the processing conditions. Research sponsored by the U.S. Dept. of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Div. (synthesis science) and Scientific User Facilities Div. (characterization science).

[1] Kazansky P. et al., “”Quill” writing with ultrashort light pulses in transparent materials”, Appl. Phys. Lett., Vol. 90, 151120, 2007 [2] Taylor R., “Application of femtosecond laser induced self-organized planar nanocracks inside fused silica glass”, Laser & Photon. Rev. 2, No. 1-2, 26-46, 2008

Return to Contents

+1 360 676 3290 · [email protected]

159

Conference 9738: Laser 3D Manufacturing III Monday - Thursday 15–18 February 2016 Part of Proceedings of SPIE Vol. 9738 Laser 3D Manufacturing III

9738-1, Session 1

9738-3, Session 2

Improvement in contact resistance of 4H-SiC by excimer laser doping using silicon nitride films

Laser-assisted inkjet printing of highly viscous fluids with sub-nozzle resolution

Ryota Kojima, Hiroshi Ikenoue, Masaru Suwa, Akihiro Ikeda, Daisuke Nakamura, Tanemasa Asano, Tatsuo Okada, Kyushu Univ. (Japan) We have proposed a novel method of low-temperature nitrogen doping into 4H-SiC(0001) induced by KrF excimer laser irradiation to a SiNx film. The SiNx film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. Laser beam size on the sample surface was 300 ?m?300 ?m. Irradiation fluence was 1.0 J/ cm2-4.0 J/cm2, and the number of shots was from 1 shot to 30 shots. Laser irradiation was performed in a vacuum chamber to avoid oxidation of the SiC surface. High concentration nitrogen doping (~1?1020 /cm3 at the surface) and very low contact resistance with ohmic I-V characteristics can be achieved by laser ablation of the SiNx film. In the case of laser irradiation of 1.5 J/cm2 and above 5 shots, the SiNx film was almost ablated without laser ablation of the SiC substrate. Then, excellent ohmic contact characteristics was obtained at the irradiation number of 5 shots, and it was hardly deteriorated up to 30 shots. In the case of irradiation fluence above 2.5 J/cm2, ablation of the SiC substrates was induced and ohmic contact characteristics were deteriorated with increasing the number of shots. From these results, we conclude that excellent ohmic contact characteristics without irradiation damage to SiC substrates can be obtained in a stable at the irradiation fluence of 1.5 J/cm2.

9738-2, Session 1

A cantilever based optical fiber acoustic sensor fabricated by femtosecond laser micromachining Jie Liu, Lei Yuan, Clemson Univ. (United States); Jie Huang, Missouri Univ. of Science and Technology (United States); Hai Xiao, Clemson Univ. (United States) Optical fiber based acoustic pressure sensors have attracted more and more interests in recent years due to their small sizes, light weight, large young’s modulus, and immunity to electromagnetic interference. Various optical fiber structures have been investigated in/on fiber tips for acoustic sensing such as a thin-film diaphragm, a sealed cavity, a Bragg grating structure, and a micro/nano periodic structure, etc. Among these structures, femtosecond (fs) laser micromachining has been a promising mean for fabrication of micro/nano structures in/on optical fiber tips attributed to its high precision, flexible design, assembly free, and compatible with other methods such as sputtering coating, fusion splicing, etc. In this paper, we present a pure silica micro-cantilever based optical fiber sensor for acoustic pressure detection. The cantilever is directly fabricated by fs laser micromachining on an optical fiber tip functioning as an inline Fabry-Perot interferometer (FPI). The applied acoustic wave pressurizes the micro-cantilever beam and the corresponding dynamic signals can be probed by the FPI. The thickness, length, and width of the micro-cantilever beam can be flexibly designed and fabricated so that the sensitivity, frequency response, and the total measurement range can be varied to fit many practical applications. Experimental and simulation results with various designs will be presented and analyzed. Due to the assembly free fabrication of the fs-laser, multiple micro-cantilever beams could be potentially fabricated in/on a single optical fiber for quasi-distributed acoustic mapping with high spatial resolution.

160

Paul Delrot, Miguel A. Modestino, Demetri Psaltis, Christophe Moser, Ecole Polytechnique Fédérale de Lausanne (Switzerland) Drop-on-demand inkjet printing is mostly based on thermal and piezoactuation, allowing for densely packed nozzles in inkjet printers. However, the droplet diameter is typically defined by the nozzle diameter, thus limiting the range of viscosity that can be jetted to 10-100 mPa.s to prevent nozzle clogging. Here, we present a laser-assisted system for the delivery of micro-droplets of highly viscous fluids with sub-nozzle resolution. Highly focused supersonic jets have recently been demonstrated by focusing a nanosecond pulse of light into a micro-capillary filled with dyed water, hence generating a cavitation bubble. The consequent pressure wave impact on the concave free surface of the liquid generated flow-focused micro-jets. We implemented this technique for the production of low velocity microdroplets (1-4 m/s) with photopolymer inks of increasing viscosity (0.6-148 mPa.s) into a 430 µm-wide glass capillary using low laser energies (3-70 µJ). Time-resolved imaging provided details on the droplet generation. Single micro-droplets of diameter 70-80 µm were produced on demand with inks of viscosity 0.6-9 mPa.s with good controllability and reproducibility, thus enabling to print two-dimensional patterns with a precision of 13 µm. Furthermore, the primary droplet produced with the most viscous fluid was less than half of the capillary diameter. Preliminary results also showed that the process is linearly scalable to narrower capillaries (100-200 µm), thus paving the way for a compact laser-assisted inkjet printer. A possible application of the device would be additive manufacturing as the printed patterns could be consequently cured.

9738-4, Session 2

Laser-printing and femtosecond laserstructuring of electrode materials for the manufacturing of 3D lithium-ion microbatteries (Invited Paper) Johannes Pröll, Karlsruher Institut für Technologie (Germany); Heungsoo Kim, U.S. Naval Research Lab. (United States); Yijing Zheng, Peter Smyrek, Hans J. Seifert, Karlsruher Institut für Technologie (Germany); Alberto Piqué, U.S. Naval Research Lab. (United States); Wilhelm Pfleging, Karlsruher Institut für Technologie (Germany) Recently, three-dimensional (3D) electrode architectures have attracted great interest for the development of lithium-ion micro-batteries applicable for Micro-Electro-Mechanical Systems (MEMS), sensors, and hearing aids. Since commercially available micro-batteries are mainly limited in overall cell capacity by their electrode footprint, new processing strategies for increasing both capacity and electrochemical performance have to be developed. In case of standard micro-batteries, two-dimensional (2D) electrode arrangements are applied with thicknesses up to 200 µm. These electrode layers are composed of active material, conductive agent, graphite, and polymeric binder. Nevertheless, with respect to the type of active material, the active material to conductive agent ratio, and the film thickness, such thick-films suffer from low ionic and electronic conductivities, poor electrolyte accessibility, and finally, limited electrochemical performance under challenging conditions. In order to overcome these drawbacks, 3D electrode arrangements are

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9738: Laser 3D Manufacturing III under intense investigation since they allow for the reduction of lithiumion diffusion pathways in between interdigitated electrodes, even for electrodes with enhanced mass loadings. In this paper, we present how to combine laser-printing and femtosecond laser-structuring for the development of advanced 3D electrodes composed of LiFePO4 (LFP) and LiNi1/3Mn1/3Co1/3O2 (NMC). In a first step, LFP and NMC thick-films were laser-printed and calendered to produce film thicknesses in the range of 30 µm - 200 µm. In a second step, femtosecond laser-structuring was carried out to form 3D architectures directly into thick-films. Finally, electrochemical cycling of laser-processed films was performed in order to evaluate the most promising 3D electrode design suitable for application in long life-time 3D micro-batteries.

9738-5, Session 5

Cloaked contact fingers on solar cells enabled by 3D laser lithography (Invited Paper) Martin F. Schumann, Karlsruher Institut für Technologie (Germany); Samuel Wiesendanger, Friedrich-Schiller-Univ. Jena (Germany); Jan Christoph Goldschmidt, Benedikt Bläsi, Fraunhofer-Institut für Solare Energiesysteme (Germany); Karsten Bittkau, Ulrich W. Paetzold, Forschungszentrum Jülich GmbH (Germany); Alexander N. Sprafke, Martin-Luther Univ. Halle-Wittenberg (Germany); Ralf B. Wehrspohn, Martin-Luther Univ. Halle-Wittenberg (Germany) and Fraunhofer-Institut für Werkstoffmechanik (Germany); Carsten Rockstuhl, Martin Wegener, Karlsruher Institut für Technologie (Germany) Metallic contact fingers on the sun-facing side of solar cells are necessary to reduce Ohmic losses but also represent optically dead regions reducing the energy conversion per area. In this talk, we present two approaches to solve this problem by “cloaking the contacts”. The first approach uses graded-index metamaterials designed by two-dimensional SchwarzChristoffel conformal maps, the second free-form surfaces designed by one-dimensional coordinate transformations. We provide proof-of-principle demonstrators using direct laser writing of polymer structures on silicon wafers with opaque metal contacts. Using the so-called shell-writing mode, fabrication times for “masters” are reduced significantly, potentially enabling mass fabrication via imprinting. We show that the free-form-surface approach completely solves the shadowing problem for all relevant angles of incidence, all polarizations, and colors of sunlight for contact coverages up to about 20%. Typical present coverages are below 10%. Moreover the free-form approach is amenable to mass fabrication by making a “master” by direct laser writing and then using this “master” for printing. Due to the special shape of the free-form surface, the required micrometer dimensions, and the necessary surface smoothness, direct laser writing is presently the only possible means for fabricating the “master”.

9738-6, Session 5

Precise 3D printing of micro/ nanostructures using highly conductive carbon nanotube-acrylate composites Ying Liu, Wei Xiong, Li Jia Jiang, Yunshen Zhou, Yongfeng Lu, Univ. of Nebraska-Lincoln (United States) Two-photon polymerization (TPP) is of increasing interest due to its unique combination of truly 3D fabrication capability and ultrahigh spatial resolution of ~100 nm. However, the stringent requirements of non-linear resins seriously limit the material functionality of 3D printing via TPP. Precise fabrication of 3D micro/nanostructures with multi-functionalities such as

Return to Contents

high electrical conductance and strength is still a long-standing challenge. In this work, TPP fabrication of arbitrary 3D micro/nanostructures using multi-walled carbon nanotube (MWNT)-acrylate composite resins has been developed. Up to 0.2 wt% MWCNTs have been incorporated into thiolacrylate resins to form highly uniform and stable composite photoresists without obvious degradation for one week at room temperature. Various functional 3D micro/nanostructures including woodpiles, microcantilevers, suspended microbridges, microcoil arrays, and complex microcars have been successfully fabricated by TPP and characterized by scanning electron microscopy, Raman spectroscopy, and fluorescence spectroscopy. Comparing with conventional acrylate based resins, the MWNT-acrylate composite resin offers significant enhancements in electrical conductivity (from insulating polymer to conductive composite, 2?103 S/m) and mechanical strength (2.08 GPa in reduced Young’s Modulus, 1.3-fold enhancement; 113 KPa in hardness, 1.7-fold enhancement), and at the same time, preserving a high optical transmittance (95 % at 550 nm for 3 um film) and flexibility. The micro/nanofabrication technique based on the MWNTacrylate composite resins enables the precise fabrication of arbitrary 3D micro/nanostructures of high conductivity, strength, and low shrinkage, which promises a wide range of device applications, including MEMS/NEMS, 3D electronics, integrated optics, biomimetics, and metamaterials.

9738-7, Session 5

Potential for GPC-based laser direct writing Andrew R. Bañas, OptoRobotix ApS (Denmark); Jesper Glückstad, Technical Univ. of Denmark (Denmark) Generalized Phase Contrast (GPC) is a light efficient method for generating speckle-free contiguous optical distributions using binary-only or analog phase levels. GPC has been used in applications such as optical trapping and manipulation, active microscopy, structured illumination, optical security, parallel laser marking and recently in contemporary biophotonics applications such as for adaptive and parallel two-photon optogenetics and neurophotonics. We will present our most recent GPC developments geared towards these applications. First, a compact GPC Light Shaper implementation based on our latest theoretical derivations is used to demonstrate the benefits for typical applications where lasers have to be actively shaped into particular light patterns. We then show the potential of GPC for biomedical and multispectral applications where we experimentally demonstrate the active light shaping of a supercontinuum laser over most of the visible wavelength range. Finally, we demonstrate how GPC can be advantageously applied for fully parallel and non-scanning Laser Direct Writing of 3D structures using two-photon excitation pulsed laser sources.

9738-8, Session 6

3D light robotics (Invited Paper) Jesper Glückstad, Technical Univ. of Denmark (Denmark) The 2014 Nobel Prize on nanoscopy has cemented that optics is a key enabling technology for getting a grasp of the micro- and nano-world. By creatively combining a host of complementary approaches one can today realize advanced optical modalities that integrate an increasing number of functionalities and augment not just passive observation but also active access and control over the nanoworld. Using a merger of light and matter sculpting, we have laser-fabricated free-floating waveguides that can be optically trapped and remote-controlled in a volume; hence coined Waveguided Optical Waveguides (WOWs). Combining 3D laser-based microfabrication with 3D optical trapping and manipulation allows us to exploit these WOWs in versatile and dynamically reconfigurable architectures. A plurality of counter-propagating beam-traps relayed to the trapping volume by low-NA microscope objectives on our Biophotonics Worskstation (BWS) control the WOW-structures demonstrating the possibility for a structuremediated paradigm where micron-sized tools are used to achieve optical near-field tip-size access in 3D. However, realizing the full potential of this

+1 360 676 3290 · [email protected]

161

Conference 9738: Laser 3D Manufacturing III new structure-mediated approach in challenging microscopic geometries requires a versatile 3D light coupling that can dynamically track a plurality of WOWs to ensure continuous optimal light probing.

material will open a wider range of exciting applications.

9738-9, Session 6

[2] Jiguet, S., Bertsch, A., Hofmann, H. and Renaud P., „Conductive SU8 Photoresist for Microfabrication“, Adv. Funct. Mater. 15, 1511–1516 (2005).

Manufacturing of functional micro/nano structures by fs-laser microfabrication

[3] Benlarbi, M., Blum, L. J. and Marquette, C. A., „SU-8-carbon composite as conductive photoresist for biochip applications“, Biosens. Bioelectron. 38, 220–225 (2012).

Cleber R. Mendonça, Nathália B. Tomazio, Franciele Henrique, Adriano J. G. Otuka, Juliana M. P. Almeida, Instituto de Física de São Carlos (Brazil); Carla R. Fontana, Univ. Estadual Paulista “Júlio de Mesquita Filho” (Brazil)

[4] Hauptman, N., Zveglic, M., Macek, M. and Gunde M. K., „Carbon based conductive photoresist“, J. Mater. Sci. 44, 4625–4632, (2009).

Femtosecond laser microfabrication has been shown to be a powerful tool for manufacturing advanced materials, aiming at applications from photonics to biology. The nonlinear nature of the light-mater interaction, achieved with fs-pulses, confines the induced changes to the focus of the laser, which has allowed the fabrication of complex three-dimensional microstructures. fs-microfabrication methods have been used to produce photonic crystals, waveguides, micromechanical actuators, scaffolds for biological applications, etc. Most of the microstructures reported, however, are passive elements, whose properties are not usually changed by external means. In this direction, our work has been focused on the development of strategies to produce functional microstructures by fs-laser fabrication methods. In this work we present results on the fabrication of light emitting devices, waveguides containing metal nanoparticles, micro-optical storage devices and microstructures for biological applications, using either multiphoton lithography or fs-laser micromachining. Results on the optical, mechanical and bio-related properties will be presented, which indicate the approach proposed as a promising tool for the development of applications from displays to tissue engineering. The authors acknowledge FAPESP (2011/12399-0), CNPq, CAPES and the Air Force Office of Scientific Research (FA9550-12-1-0028) for financial support.

[6] Lu, W., Zhang, Y., Zheng, M., Jia, Y., Liu, J., Dong, X., Zhao, Z., Li, C., Xia, Y., Ye, T. and Duan, X., “Femtosecond direct laser writing of gold nanostructures by ionic liquid assisted multiphoton photoreduction”, Opt. Mater. Express 3, 1660–1673 (2013).

9738-10, Session 6

Bernd Reutterer, Lukas Traxler, Natascha Bayer, Andreas Drauschke, Fachhochschule Technikum Wien (Austria)

Advanced two-photon photolithography for patterning of transparent, electrically conductive ionic liquid-polymer nanostructures (Invited Paper) Natalia A. Bakhtina, Neil MacKinnon, Jan G. Korvink, Karlsruher Institut für Technologie (Germany) A key challenge in micro- and nanotechnology is the direct patterning of functional structures. For example, it is highly desirable to possess the ability to create three-dimensional (3D), conductive, and optically transparent structures. Efforts in this direction have, to date, yielded less than optimal results since the polymer composites had low optical transparency over the visible range, were only slightly conductive, or incompatible with high resolution structuring.1-6 We have previously presented the novel crosslinkable, conductive, highly transparent composite material based on a photoresist (IP-L 780, OrmoComp, or SU-8) and the ionic liquid 1-butyl3-methylimidazolium dicyanamide.7-8 Material patterning by conventional and two-photon photolithography has been demonstrated as proof-ofconcept. Aiming to increase the resolution and to extend the spectrum of exciting applications we continued our research into identifying new ionic liquid - polymer composites. In this paper, we report the precise 3D singlestep structuring of ionic liquid - polymer nanostructures with excellent optical and electrical characteristics. This was achieved via the development of novel crosslinkable composite based on the photoresist IP-G 780 and the ionic liquid 1-butyl-3-methylimidazolium dicyanamide. The successful combination of the developed material with the advanced direct laser writing technique enabled the time- and cost-saving direct manufacturing of transparent, electrically conductive components with a resolution down to 150 nm. We believe that the excellent characteristics of the structured

162

[1] Abargues, R., Rodriguez-Canto, P. J., Garcia-Calzada, R. and J. MartinezPastor, „Patterning of Conducting Polymers Using UV Lithography: The in-Situ Polymerization Approach“, J. Phys. Chem. C 116, 17547–17553 (2012).

[5] Annaiyan, U. M., Kalantar-zadeh, K., Fang, Q. and Cosic, I., “Development of a conductive photoresist with a mixture of SU-8 and HCL doped polyaniline”, Proc. IEEE Tencon 2005, 1B 07.2. (2005).

[7] Bakhtina, N. A., Voigt, A., MacKinnon, N., Ahrens, G., Gruetzner, G., Korvink, J. G., Novel ionic liquid - polymer composite and an approach for its patterning by conventional photolithography, Proc. IEEE MEMS 2015, 97–101 (2015). [8] Bakhtina, N. A., Loeffelmann, U., MacKinnon, N., Korvink, J. G., “Twophoton nanolithography enhances performance of an ionic liquid - polymer composite sensor”, Adv. Funct. Mater. 25, 1683-1693 (2015).

9738-38, Session PTue

Experiments for practical education in process parameter optimization for selective laser sintering to increase workpiece quality

Selective Laser Sintering (SLS) is considered as one of the most important additive manufacturing processes due to component stability and its broad range of usable materials. However the influence of the different process parameters on mechanical workpiece properties are still poorly studied, leading to the fact that further optimization is necessary to increase workpiece quality. In order to investigate the impact of various process parameters, laboratory experiments are implemented to improve the understanding of the SLS limitations and advantages on an educational level. Experiments are based on two different workstations, used to teach students the fundamentals of SLS. First of all a CO2 laser workstation is used to investigate the interaction of the laser beam with the used material in accordance with varied process parameters to analyze a single-layered test piece. Second of all the FORMIGA P110 laser sintering system from EOS is used to print different 3D test pieces in dependence on various process parameters. Finally quality attributes are tested including warpage, dimension accuracy, surface quality or tensile strength. For dimension measurements and evaluation of the surface structure a telecentric lens in combination with a camera is used. A tensile test machine allows testing of the tensile strength and the interpreting of stress-strain curves. The developed laboratory experiments are suitable to teach students the influence of processing parameters. In this context they will be able to optimize the input parameters depending on the component which has to be manufactured and to increase the overall quality of the final workpiece.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9738: Laser 3D Manufacturing III

9738-41, Session PTue

9738-43, Session PTue

Optically active acrylate/SWCNT composite microdevices produced by multi-photon polymerization

Laser point cloud registration in object 3D reconstruction

Adriano Jose Galvani Otuka, Instituto de Física de São Carlos (Brazil); Gustavo F. Almeida, Cleber R. Mendonça, Univ. de São Paulo (Brazil) Functionalized polymeric microdevices have been widely investigated in several technological researches. There are a wide range of materials which can be used to functionalize polymeric matrices. For instance, single walled carbon nanotubes (SWCNT) can promote mechanical improvement and enhance electrical properties of polymeric composites. Organic dyes can change optical properties of polymeric matrices, allowing selective fluorescence control from the ultraviolet to near-infrared. However, only a few studies have focused on the functionalization of polymers using different materials. In this work, we fabricated polymeric composites microdevices, functionalized with SWCNT and organic dyes, using multiphoton absorption polymerization. SWCNT functionalized with carboxylic acid were mixed to the liquid resin composed by equal proportions of two triacrylate monomers: tris(2-hydroxyethyl) isocyanurate triacrylate and ethoxylated(6) trimethylolpropane triacrylate. After this step, organic dyes, such as Rhodamine B or Disodium Fluorescein, are added to the SWCNTresin. To fabricate these structures, we use a Ti:sapphire laser (operating at 780 nm, 150 fs) focused through a microscope objective (0.85-NA) in the volume of the polymeric resin. The laser is scanned in the sample using a pair of galvanometric mirror (xy plan) and a motorized stage (z-axis). Our results indicated changes in the mechanical properties of the sample containing SWCNT, such as in the elastic modulus and viscoelasticity. Additionally, optical properties of the dyes were preserved in this fabrication method. The approach presented here is a promising alternative for functionalization of polymers, enabling the production of devices with special features for different fields.

9738-42, Session PTue

Maskless lithography stage-shutter-free microfabrication based on serial areacontrolled hologram Chenchu Zhang, Jingjing Zhang, Yanlei Hu, Jiawen Li, Zhaoxin Lao, Ze Cai, Dong Wu, Jiaru Chu, Univ. of Science and Technology of China (China) We demonstrate a maskless lithographic system to perform serial micropatterning based on two photon polymerization (TPP). We present a stage-shutter-free microfabrication approach to achieve arbitrary three dimensional (3D) micro structures without the use of 3D stage and shutter. The Gerchberg-Saxton algorithm and a spatial light modulator (SLM) have been used to create and display phase holograms. The position of focus can be controlled by varying the phase holograms. However, some constraints such as phase quantization and dead space (those regions between pixels) will introduce undesired imperfection of the target patterns, especially foci nonuniformity, which will obviously affect the fabrication quality. An easy and efficient area-controlled approach is provided to increase the uniformity of focus in order to get 3D micro structures with higher quality. The dead space of SLM can be considered as a two dimensional (2D) grating, so that the desired multifoci pattern has an envelope of a 2D grating diffraction function, which elucidates the reason of uniformity reduction of the reconstruction pattern. Here we apply holograms with different active size based on the diffraction function of 2D grating to eliminate the nonuniformity of target focus. Several cubes are made and compared to optimize the fabrication parameters. In the end, a 3D Olympic Games logo was fabricated without moving stage and shutter, showing the promising application in cost reduction of 3D integrated TPP fabrication systems.

Return to Contents

Da Liu, Chunyan Li, Beijing Institute of Control Engineering (China); Fang Yin, BeiHang Univ. (China); Yi Li, Li Wang, Beijing Institute of Control Engineering (China) Laser point cloud registration is widely utilized in object 3D reconstruction and object measure. In the process, the point cloud from multiple laser scans in arbitrary initial position is identified and matched each other with corresponding rigid transforms. In the paper, 4 to 6 key point are adaptive extracted from the point cloud according the character of the point cloud. Firstly, four key points are selected according to the surface area. Then the fifth and sixth point are selected according to the normal and cubage of all the key point. The four key point in the first step and six key point in the second step are separately utilized to shape matching. The match error of the four point and six point are calculated separately. If the difference of match error in four points and six points is less than a threshold, the match is terminated. Otherwise, the next key point is selected according to the normal and cubage of all the key point. The match error before and after the new added key points are calculated separately. If the difference of match error is less than a threshold, the match is terminated, otherwise a new key point is selected and added for match. The robustness of the algorithm is demonstrated on several sets of multiple range scans with varying degree of noise and extent of overlap. The experimental results show that the proposed method is fast and robust, and are resilient to noise and outliers.

9738-44, Session PTue

Improving accuracy of overhanging structures for selective laser melting through reliability characterization of single track formation on thick powder beds Sankhya Mohanty, Jesper H. Hattel, Technical Univ. of Denmark (Denmark) Repeatability and reproducibility of parts produced by selective laser melting is a standing issue, and coupled with a lack of standardized quality control presents a major hindrance towards maturing of selective laser melting as an industrial scale process. Consequently, numerical process modelling has been adopted towards improving the predictability of the outputs from the selective laser melting process. Establishing the reliability of the process, however, is still a challenge, especially in components having overhanging structures. In this paper, a systematic approach towards establishing reliability of overhanging structure production by selective laser melting has been adopted. A calibrated, fast, multiscale thermal model is used to simulate the single track formation on a thick powder bed. Single tracks are manufactured on a thick powder bed using same processing parameters, but at different locations in a powder bed and in different laser scanning directions. The difference in melt track widths and depths captures the effect of changes in incident beam power distribution due to location and processing direction. The experimental results are used in combination with numerical model, and subjected to uncertainty and reliability analysis. Cumulative probability distribution functions obtained for melt track widths and depths are found to be coherent with observed experimental values. The technique is subsequently extended for reliability characterization of single- and multiple layers produced on a thick powder bed without support structures, by determining cumulative probability distribution functions for average layer thickness, sample density and thermal homogeneity.

+1 360 676 3290 · [email protected]

163

Conference 9738: Laser 3D Manufacturing III

9738-45, Session PTue

9738-12, Session 7

Experimental study on Ti alloy plate fabrication by vacuum selective laser melting

Laser printing of 3D metallic interconnects

Yuji Sato, Masahiro Tsukamoto, Osaka Univ. (Japan); Yorihiro Yamashita, Industrial Research Institute of Ishikawa (Japan); Shinichiro Masuno, Nobuyuki Abe, Osaka Univ. (Japan)

The use of laser-induced forward transfer (LIFT) techniques for the printing of functional materials has been demonstrated for numerous applications. Traditionally, the printing results in 2D patterns being generated nonlithographically, while more recently various groups have demonstrated electrical interconnects from laser printed 3D structures. The laser printing of these interconnects takes place through aggregation of voxels of either molten metal or of dispersed metallic nanoparticles. However, the generated 3D structures do not posses the same metallic conductivity as a bulk metal interconnect of the same cross-section and length as those formed by wire bonding or tab welding. It is possible, however, to laser transfer entire structures using a technique developed at NRL known as lase-and-place. Lase-and-place is a LIFT process whereby whole components and parts can be transferred from a donor substrate onto a desired location with one single laser pulse. This paper will describe the use of LIFT to laser print freestanding, solid metal interconnects precisely over devices contact pads to make functional circuits. Furthermore, this paper will also show how the same laser can be used to bend or fold the bulk metal foils prior to transfer, thus forming compliant 3D structures able to provide strain relief for flexible circuits or thermal mismatch. These interconnect “bridges” can span wide gaps (on the order of several hundred microns) and accommodate height differences of tens of micron between adjacent devices. Examples of these laser printed 3D metallic bridges and their role in the development of next generation electronics by additive manufacturing will be presented.

Selective laser melting (SLM), one of an additive manufacturing technologies, is useful tools for direct and complicated shape formation. We demonstrated that a Ti-6Al-4V plate, which is clinically used for artificial bone and hard tissue implant in humans because of their light and biocompatibility, were fabricated by SLM process in vacuum. The Ti64 powder has a spherical shape with a particle size distribution from 4 to 88 ?m. The chamber’s pressure was set to 1.0?10-2 Pa to prevent the Ti64 powder from oxidizing. The base plate of the powder bed was vertically dropped in determined steps, and Ti64 powder supplied from the powder feeder was then smoothed by a roller on top of the powder bed. The singlemode fiber laser irradiated and melted the powder bed to make a molten pool in order to form 2D metallic structures. In order to investigate the laser melting and solidification dynamics, a process of Ti 64 plate fabrication (10mm x 10mm x1 mm) was captured by high speed video camera. It was also determined that crystal orientation was evaluated with X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. From EDX analysis, the chemical compounds were not changed from powder to fabricated sample. And it was recorded from the powder peaks of ? (1011), ? (0002), ? (1010), and ? (1012) that the crystal orientation is composed mainly of martensitic alpha by XRD. Diffraction peaks corresponding to ? (110) were detected in vacuum SLM processed samples.

9738-11, Session 7

Laser induced forward transfer: A technique for 3D manufacturing of functional devices (Invited Paper) Ioanna Zergioti, National Technical Univ. of Athens (Greece) This paper reviews the latest developments and the background of Laser Induced Forward Transfer as a 3D manufacturing approach for functional devices with applications in organic electronics and in biotechnology. Current technological trends require the precise deposition of highly resolved features, in a direct writing approach which preserve their structural and electronic properties upon transfer, while increasing the number of components that can be integrated in a single device. Laser Induced Forward Transfer meets these requirements. Examples of selected applications, including organic thin-film transistors, metallic interconnects, circuits defects repairing, chemical sensors and biosensors will be presented, highlighting the potential incorporation of lasers into the direct printing of entire devices and components. In particular, the successful laser printing of polymers, metals, semiconducting inks, 2D nanomaterials, and viable biological materials such as DNA, proteins and enzymes with high spatial resolution offers unique advantages as compared to traditional inkjet and thin film techniques. Moreover, the mechanisms of liquid and solid phase LIFT through time-resolved studies will be discussed, while post printing processes such as laser sintering will also be addressed.

164

Alberto Piqué, Iyoel Beniam, Scott A Mathews, Nicholas A. Charipar, U.S. Naval Research Lab. (United States)

This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

9738-13, Session 7

Characterization of transfer regimes of high-viscosity silver pastes printed by LIFT David Munoz-Martin, Univ. Politécnica de Madrid (Spain); C. Frederik Brasz, Princeton Univ. (United States); Chen Yu, Miguel Morales, Univ. Politécnica de Madrid (Spain); Craig B. Arnold, Princeton Univ. (United States); Carlos Molpeceres, Univ. Politécnica de Madrid (Spain) Laser induced forward transfer (LIFT) technique can be used for printing metallic contacts onto flexible optoelectronics devices in flex/3D electronics industry, patterning solder paste for microelectronics or for the metallization of the front side of solar cells. In the latter case, one of the aims of solar cell researchers and manufacturers is to find technologies leading to an increase in the efficiencies of solar cells while keeping costs low. Specifically, procedures capable of making better contacts by improving the aspect ratio and decreasing contact losses are sough. In this work, a study of LIFT of single dots of a high viscosity silver paste, designed for screen-printing of solar cells, was performed using a ns-pulsed laser at 532 nm. Phenomenological and analytical descriptions are given of the influence of process parameters on the morphology of transferred paste dots characterized by means of confocal microscopy. Time-resolved imaging was implemented in another LIFT dotting experiment with similar experimental conditions in order to illuminate the transfer dynamics in relation to the pulse energy and paste thickness. Four transfer regimes are defined in accordance with the observed distinctive paste dot morphologies on the acceptor: non-dot transfer, in which the pulse energy is below the transfer threshold of a given paste thickness; cluster-dot transfer, where the dot size increases as a function of pulse energy for relatively thin films of paste; concrete-dot transfer, when the paste is thick enough to allow the protruding jet to impact the acceptor substrate without separating from the donor substrate; and explosion-dot transfer, where the high laser pulse energy generates a bursting ejection on the donor that splashes paste on the acceptor.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9738: Laser 3D Manufacturing III

9738-14, Session 8

3D manufacturing of micro and nanoarchitected materials (Invited Paper) Lorenzo Valdevit, Univ. of California, Irvine (United States) Reducing mass without sacrificing mechanical integrity and performance is a critical goal in a vast range of applications. Introducing a controlled amount of porosity in a strong and dense material (hence fabricating a cellular solid) is an obvious avenue to weight reduction. The mechanical effectiveness of this strategy, though, depends strongly on the architecture of the resulting cellular material (i.e., the topology of the introduced porosity). Recent progress in additive manufacturing enables fabrication of macro-scale cellular materials (both single-phase and hybrid) with unprecedented dimensional control on the unit-cell and sub-unit-cell features, potentially producing architectures with structural hierarchy from the nano to the macro-scale. As mechanical properties of materials often exhibit beneficial size effects at the nanoscale (e.g., strengthening of metals and toughening of ceramics), these novel manufacturing approaches provide a unique opportunity to translate these beneficial effects to the macroscale, further improving the mechanical performance of architected materials. In this presentation, I will review a number of advanced manufacturing technologies that allow fabrication of 3D architected materials with high structural hierarchy, and provide recent examples of micro and nanoarchitected materials with superior combinations of properties. The urgent need to form strong synergies among the fields of additive manufacturing, topology optimization and architecture-properties relations will be emphasized throughout.

9738-15, Session 8

Aperiodic mechanical metamaterial: Bridging the gap between matter and machine (Invited Paper) Corentin Coulais, Leiden Univ. (Netherlands) Mechanical metamaterials exhibit a wide range of unusual properties, including negative response, cloaking, topological insulation and programmability. Such materials consist of periodic stackings of unit cells, where the unit cell design encodes the materials functionality. This periodicity limits their potential, as these metamaterials exhibit a homogeneous response. Here we introduce a combinatorial strategy to create a vast number of distinct, three-dimensional mechanical metamaterials. These materials consist of aperiodic stackings of anisotropic unit cells, and their functionality results from both the unit cell and the stacking order. We create such metamaterials by 3D printing, and experimentally demonstrate that the information embedded in the stacking order spawns completely novel properties. First, their surfaces can morph into an arbitrary texture. Second, their mechanics is sensitive to the pattern of the surface they are in contact with. Our combinatorial approach opens pathways for the design of functional structures programmed with specific mechanical tasks, which blur the boundary between material and machine.

9738-16, Session 8

The TEMPS facility for optical property metrology of materials at high temperatures: Goals and current status Sergey Mekhontsev, Weston L. Tew, Steven E. Grantham, Vladimir B. Khromchenko, Leonard M. Hanssen, National Institute of Standards and Technology (United States)

Return to Contents

Knowledge of the optical properties of materials such as spectral emittance and reflectance is essential for non-contact thermometry, heat transfer modeling, and prediction of directed energy source coupling with targets (for example, in laser-based material processing and manufacturing). Even the common “emissivity-free” multi-spectral methods of radiation thermometry, which do require absolute knowledge of emittance, can greatly benefit from validation using well-characterized materials of interest along with accurate absolute temperature measurements of the surface. TEMPS (Temperature and Emittance of Melts, Powders and Solids) is a new facility under construction at NIST, which is designed for the accurate measurement of material emittance, reflectance and true surface temperature and is aimed at the establishment of measurement traceability and best practices for non-contact thermometry in additive manufacturing. This will enable improvements in the reproducibility and control of manufacturing processes. This paper describes the objectives, goals, and development status of this facility.

9738-17, Session 8

Electrochemistry and corrosion of multimetal printed structures (Invited Paper) Owen Hildreth, Arizona State Univ. (United States); Timothy W. Simpson, The Pennsylvania State Univ. (United States) Advances in metallic 3D printing combined with renewed interests in additive manufacturing have opened up a host of new technologies and ideas for both the applications of lasers and the exploration of new material systems. Newer multi-metal powder-flow laser melt/sintering printers is one of the key technologies that enable scientists to study complex metallic systems in a rapid manner. While publications detail the mechanical and physical properties of multi-metal, heterogeneous printed structures, there has been very little reported on the electrochemical and corrosion stability of these new material structures. This paper details the electrochemical and corrosion properties of metallic structures printed using multi-metal powder-flow laser sintering techniques. Particular attention is given to how both printing process and post-printing heat treatments impact the electrochemical and corrosion behaviors of the metal/metal interface.

9738-18, Session 8

Laser powder injection additive manufacturing of novel alloys and composites (Invited Paper) Baolong Zheng, Yizhang Zhou, Univ. of California, Irvine (United States); Nancy Y. C. Yang, Sandia National Labs. (United States); Enrique J. Lavernia, Julie M. Schoenung, Univ. of California, Irvine (United States) Additive manufacturing (AM) has evolved from rapid prototyping to 3D printing manufacturing that can create parts directly from CAD solid models without the use of tooling. Among various AM processing, laser engineered net shaping (LENS) is one of the fastest growing laser powder injection deposition processes. In this report, recent research and progress associated with development of alloys and composites using LENS are reviewed, such as Fe- and Ti-based alloys, Ti+TiC and Ni+TiC composites, Al+Al3Ni composite foam, and WC+Co cermets. In addition to fabricating complex geometries of dense metals and composites, the microstructure can be tailored by controlling both composition and process parameters. For processing improvement, the closed-loop diagnostics and controls with in-situ molten pool sensor and Z-height control subsystems are being developed, while the thermal behavior measurement with thermal imaging and thermocouple methods, and numerical simulation are also being extensively investigated. The trends and challenges associated with direct laser fabrication of novel materials, as well as existing problems with residual stress and porosity in deposited materials are also discussed.

+1 360 676 3290 · [email protected]

165

Conference 9738: Laser 3D Manufacturing III

9738-19, Session 9

9738-21, Session 9

Modeling the metal additive manufacturing process at the scale of the part and the powder (Invited Paper)

Sensing for directed energy deposition and powder bed fusion additive manufacturing at Penn State University (Invited Paper)

Wayne King, Lawrence Livermore National Lab. (United States) The metal laser powder bed fusion additive manufacturing process uses high power lasers to build parts layer upon layer by melting fine metal powders. Certification of parts produced using this technology is broadly recognized as a significant challenge. There are two elements that have been identified as being foundational to certification of additively manufactured metal parte: (1) physics-based process models and (2) inline process monitoring and control. In this presentation, we discuss a multiscale (length and time) modeling strategy that will serve as the foundation upon which process control and part certification can be built. These include a model at the scale of the powder that addresses the question, “Can a metal powder be processed by additive manufacturing and what are the optimal processing conditions?”, simulates single track/single-multi layer builds, and provides powder bed and melt pool thermal data. A second model computationally builds a complete part and predicts manufactured properties (residual stress, density, dimensional accuracy) in 3D. Modeling is tied to experiment through real-time in line process monitoring using a high-speed infrared camera that images the melt pool. In this presentation, we focus on how the metal powders are modeled including the interaction of the laser with the powder layer and the effects of powder size distribution

9738-20, Session 9

Towards in-situ process monitoring in selective laser sintering using optical coherence tomography Guangying Guan, The Univ. of Nottingham (United Kingdom); Zeng H. Lu, The Univ. of Sheffield (United Kingdom); Matthias Hirsch, Ruth Goodridge, The Univ. of Nottingham (United Kingdom); David T. D. Childs, Stephen J. Matcher, The Univ. of Sheffield (United Kingdom); Adam T. Clare, The Univ. of Nottingham (United Kingdom); Kristian M. Groom, The Univ. of Sheffield (United Kingdom) Selective laser sintering (SLS) enables the fast, flexible and cost-efficient production of polymer parts directly from 3D CAD. However, there is a marked lack of process monitoring and feedback control of key process variables in SLS, preventing its wider uptake in high-value or safety critical applications. In this study, optical coherence tomography (OCT) is used for the first time to evaluate components produced by SLS. Surface defects in Polyamide parts are analyzed ex-situ and the limiting factors associated with the measurement technique are quantified. OCT is compared with X-ray computed tomography (XCT) and is shown to be a powerful technique for evaluating surface irregularities and sub-surface defects that have resulted from poor sintering or non-homogeneous powder spreading. We demonstrate detection and quantification of surface defects such as cracks, pores and voids on a ~30 µm scale, using a commercial 1300nm OCT system. Furthermore, we show that this technique can resolve fine features incorporated within a 200 to 400µm depth below the surface, covering typical layer thicknesses used in SLS. Sub-surface features typical of those observed in SLS, such as voids, contaminants and regions of controlled porosity, are built into the part and are both examined and compared with the process parameters. This capability paves the way for real-time monitoring of the SLS process for assurance, or even dynamic correction of defects during part manufacture, and will also save time and material wasted in poorly sintered parts.

166

Edward W. Reutzel, Abdalla R. Nassar, John P. Morgan Jr., Donald J. Natale, Sean D. Knecht, Richard L. Tutwiler, Applied Research Lab. (United States) Additive manufacturing of metal components through directed energy deposition or powder bed fusion is a complex undertaking, often involving hundreds or thousands of individual laser deposits. During processing, conditions may fluctuate, e.g. material feed rate, beam power, surrounding gas composition, local and global temperature, build geometry, etc., leading to unintended variations in final part geometry, microstructure and properties. To assess or control as-deposited quality, researchers have used a variety of methods, including those based on sensing of melt pool and plume emission characteristics, characteristics of powder application, and layerwise imaging. Here, a summary of ongoing process monitoring activities at Penn State is provided, along with a discussion of recent advancements in the area of layerwise image acquisition and analysis during powder bed fusion processing. Specifically, methods that enable direct comparisons of CAD model, build images, and 3D microtomographic scan data will be covered, along with thoughts on how such analyses can be related to overall process quality.

9738-22, Session 9

Optical design and initial results from NIST’s AMMT/TEMPS Facility Steven E. Grantham, Brandon Lane, Jorge E. Neira, Sergey Mekhontsev, Mihaela Vlasea, Leonard M. Hanssen, National Institute of Standards and Technology (United States) NIST’s Physical Measurement and Engineering Laboratories are jointly developing the Additive Manufacturing Measurement Testbed (AMMT)/ Temperature and Emittance of Melts, Powders and Solids (TEMPS) facilities. These facilities will be co-located on an open architecture laser-based powder bed fusion system allowing users full access to the system’s operation parameters. This will provide users with access to machineindependent monitoring and control of the powder bed fusion process. In this paper there will be emphasis the AMMT which incorporates in-line visible light collection optics for monitoring and feedback control of the powder bed fusion process. We shall present an overview of the AMMT/ TEMPs program and it goals. The optical and mechanical design of the open architecture powder-bed fusion system and the AMMT will be also be described. In addition, preliminary measurement results from the system along with the current system status of and future plans the will be discussed.

9738-23, Session 9

Towards photo-induced swimming: actuation of liquid crystalline elastomer in water (Invited Paper) Giacomo Cerretti, Daniele Martella, Hao Zeng, Camilla Parmeggiani, European Lab. for Non-linear Spectroscopy (Italy); Stefano Palagi, Max Planck Institute for Intelligent Systems (Germany); Andrew G. Mark, Max-Planck-

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9738: Laser 3D Manufacturing III Gesellschaft (Germany); Kai Melde, Max Planck Institute for Intelligent Systems (Germany); Tian Qiu, Max-PlanckInstitut für Intelligente Systeme (Germany); Peer Fischer, Max Planck Institute for Intelligent Systems (Germany); Diederik S. Wiersma, European Lab. for Non-linear Spectroscopy (Italy) The talk will cover very recent, even newer results which were just submitted to Nature Communications.

9738-24, Session 10

Femtosecond fiber laser additive manufacturing of tungsten (Invited Paper) Jian Liu, Pei Yang, Baolong Zheng, Huan Huang, Shuang Bai, PolarOnyx, Inc. (United States); Lih-Mei Yang, PolarOnyx Laser Inc. (United States) The current development focus of additive manufacturing (AM) is to produce complex shaped functional metallic components, including metals and alloys, to meet demanding requirements from different industries such as aerospace, defense and biomedicines. So far, one of the major problems has been the standardization of the optimal parameters. The setting of the appropriate processing conditions can lead to the acquisition of the desired characteristics in terms of morphology, porosity, hardness, microstructural and mechanical properties of the processed components. In this paper, additive manufacturing of Tungsten materials is investigated to study the optimal parameters space that allows the formation of a continuous layer of material by using femtosecond fiber lasers. Mechanical properties (strength and hardness) and micro-structures (grain size) of the fabricated parts are investigated to establish a relationship between material, process, and metallurgical mechanism of Tungsten components. Literature data on the CW laser process will be used as benchmark for comparison with the fs laser, in which microstructures significantly deviating from the equilibrium were obtained. Fully dense Tungsten part with refined grain and increased hardness was obtained compared with others with CW laser. The results show evidence that the fs laser based AM could promote improved mechanical properties due to controlled heat input, extreme high temperature and the more rapid cooling rates achieved compared with a CW or long pulsed laser. This can greatly benefit the applications in automobile, aerospace and biomedical industries.

9738-25, Session 10

Femtosecond laser pulse induced rapid melting and resolidification of aluminum silicon powder for additive manufacturing Tobias Ullsperger, Gabor Matthäus, Markus Rettenmayr, Friedrich-Schiller-Univ. Jena (Germany); Stefan Risse, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany); Andreas Tünnermann, Stefan Nolte, Friedrich-Schiller-Univ. Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany) Direct Metal laser sintering (DMLS) is an outstanding additive technique that enables a powder based stepwise fabrication of nearly every complex three-dimensional shape. Typically, cw or long pulse lasers are used, while the utilization of ultrashort laser pulses (USP) has been barely investigated yet. The advantages of short pulses in interaction with matter are especially the reduction of the heat affected zone and the vast cooling rate which is not achievable with conventional methods. To this end we demonstrate the feasibility of melting micro powder that consists of aluminum alloyed with

Return to Contents

silicon with the help of USP’s. In this context we investigated the influence of pulse energy, repetition rate and scanning velocity with respect to the formed melting. The experiments were performed using 500fs pulses at a wavelength of 1030nm setting the laser fluence close to the ablation threshold of the powder grains to ensure high energy deposition and avoid a transition to the gaseous phase. The influence of the temporal pulse-to-pulse separation was studied in detail in order to evaluate heat accumulation effects. We could successfully demonstrate the local melting of the powder with successive single pulses. Heat accumulation can be used to control the thermally influenced zone. The extremely high cooling rates could help to improve mechanical and thermal properties of the microstructure and offer new possibilities in the processing of light-weight elements for manifold applications in aerospace and automotive.

9738-26, Session 10

Laser post-processing of Inconel 625 made by selective laser melting David B. Witkin, Henry Helvajian, Lee F. Steffeney, William W. Hansen, The Aerospace Corp. (United States) The effect of laser remelting of surfaces of as-built Selective Laser Melted (SLM) Inconel 625 was evaluated for its potential to improve the surface roughness of SLM parts. Alloys made by SLM have properties similar to their wrought counterparts, but surface roughness of SLM-made parts is much higher than found in standard machining operations. This has implications for mechanical properties of SLM materials, such as a large debit in fatigue properties, and in applications of SLM, where surface roughness can alter fluid flow characteristics. Because complexity and net-shape fabrication are fundamental advantages of Additive Manufacturing (AM), post-processing by mechanical means to reduce surface roughness detracts from the potential utility of AM. Use of a laser to improve surface roughness by targeted remelting or annealing offers the possibility of in-situ surface polishing of AM surfaces- the same laser used to melt the powder could be amplitude modulated to smooth the part during the build. The effects of remelting the surfaces of SLM Inconel 625 were demonstrated using a CW fiber laser (IPG: 1064 nm, 2-50 W) that is amplitude modulated with a pulse profile to induce remelting without spallation or ablation. The results show that with an appropriate pulse profile that meters the heat-load, surface features such as partially sintered powder particles and surface connected porosity can be mitigated via a secondary remelting/annealing event. Techniques are also under development that can measure surface roughness during a build and thereby enable the application of a “corrective” remelting/annealing pulse if necessary.

9738-27, Session 10

Fabrication and heat treatment of high strength Al-Cu-Mg alloy processed using selective laser melting Hu Zhang, Haihong Zhu, Xiaojia Nie, Ting Qi, Zhiheng Hu, Xiaoyan Zeng, Huazhong Univ. of Science and Technology (China) The proposed paper illustrates fabrication and heat treatment of high strength Al-Cu-Mg alloy produced by selective laser melting (SLM) process. Al-Cu-Mg alloy is one of the heat treatable aluminum alloys regarded as difficult to fusion weld. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, 3D Al-CuMg parts with relative high density of 99.8% are produced by SLM from gas atomized powders. Room temperature tensile tests reveal a remarkable

+1 360 676 3290 · [email protected]

167

Conference 9738: Laser 3D Manufacturing III mechanical behavior: the samples show yield and tensile strengths of about 276 MPa and 402 MPa, respectively, along with fracture strain of 6%. The effect of solution treatment and aging treatment on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the SLMed Al-Cu-Mg samples can be tuned within a wide range of strength and ductility through proper heat treatment.

using a customized genetic algorithm developed for optimizing cellular scanning strategy for selective laser melting, with an objective of reducing residual stresses and deformations. The resulting thermo-mechanically optimized cellular scanning strategies are compared with standard scanning strategies and thermally-optimized scanning strategies which have been used to manufacture standard samples.

9738-28, Session 11

9738-30, Session 11

Additive manufacturing of glass for optical applications (Invited Paper)

Application of laser ultrasonic nondestructive evaluation technique to additive manufacturing

Junjie Luo, Luke Gilbert, Douglas A. Bristow, Robert G. Landers, Missouri Univ. of Science and Technology (United States); Jonathan T. Goldstein, Augustine M. Urbas, Air Force Research Lab. (United States); Edward C. Kinzel, Missouri Univ. of Science and Technology (United States) Additive manufacturing is becoming increasingly accepted for printing plastics, metals, and some ceramics. However, comparatively little work has been performed on printing glass and other optical components aside from polymers. Ongoing work on depositing transparent glass components will be presented including printing soda-lime, fused quartz, and optical fiber. While multiple additive manufacturing techniques can deposit glass, including powder-bed and blown-powder processes, feeding a filament directly into the melt-pool minimizes entrapping bubbles during deposition. This presentation will focus on filament-fed results. In this process a CO2 laser is used to locally heat and melt the glass. The build platform is scanned by moving a heated build platform under a stationary laser beam. Material is consolidated by the melting process, solidifies as the part translates relative to the laser beam. The key parameters for each process are identified, notably the scan speed, laser power, and feed-rates. These are mapped in terms of their effects on the morphology and optical properties of the printed glass. The relationship between these parameters is studied experimentally and corroborated with numerical simulations (ANSYS Fluent) of the melt pool temperature. We use the optimized parameters to build parts including simple convex glass lenses. The free surface of the printed part can be very smooth because the laser effectively flame polishes the part. In-situ spectrometry is used to monitor the process. The additive manufacturing process allows the material composition to be adjusted locally on a 3D volumetric basis for making gradient index optics.

9738-29, Session 11

Reducing residual stresses and deformations in selective laser melting through multilevel multiscale optimization of cellular scanning strategy Sankhya Mohanty, Jesper H. Hattel, Technical Univ. of Denmark (Denmark) Residual stresses and deformations continue to remain one of the primary challenges towards expanding the scope of selective laser melting as an industrial scale manufacturing process. While process monitoring and feedback-based process control of the process has shown significant potential, there is still dearth of techniques to tackle the issue. Numerical modelling of selective laser melting process has thus been an active area of research in the last few years. However, large computational resource requirements have slowed the usage of these models for optimizing the process.

Henry Helvajian, Anthony J. Manzo, Shant Kenderian, The Aerospace Corp. (United States) The change in properties of a propagating ultrasonic wave has been a mainstay characterization tool of the nondestructive evaluation (NDE) industry for identifying subsurface defects (e.g. damage). A variant of this concept could be applicable to 3D additive manufacturing where the existence of defects (e.g. pores) within a sublayer could mark a product as non-qualifying. We have been exploring the utility of pulsed laser ultrasonic excitation coupled with CW laser heterodyne detection as an all optical scheme for characterizing sub surface layer properties. The all-optical approach permits a straight forward integration into a laser additive processing tool. To test the concept, we have developed an experimental system that generates pulsed ultrasonic waves (the probe) with high bandwidth (>> 10MHz) and a surface displacement sensor that can capture the ultrasonic signal “return” with bandwidth close to 300 MHz. The use of high frequencies enables the detection of smaller defect sites. The technique is time resolved with the sensor and probe as point (~ 10-30 microns) beams. Current tests include characterizing properties of weld joints between two thin stainless steel plates. The long term objective is to transition the technique into a laser additive manufacturing tool.

9738-31, Session 11

Repurposing mainstream CNC machine tools for laser-based additive manufacturing (Invited Paper) Jason B. Jones, Hybrid Manufacturing Technologies (United States) The advent of laser technology has been a key enabler for industrial 3D printing, know as Additive Manufacturing (AM). Despite its commercial success and unique technical capabilities, laser-based AM systems are not yet able to produce parts with the same accuracy and surface finish as CNC machining. To enable the geometry and material freedoms afforded by AM, yet achieve the precision and productivity of CNC machining, hybrid combinations of these two processes have started to gain traction. To achieve the benefits of combined processing, laser technology has been integrated into mainstream CNC machines - effectively repurposing them as hybrid manufacturing platforms. This presentation reviews how this engineering challenge has prompted beam delivery innovations to allow automated changeover between laser processing and machining, using standard CNC tool changers. Handling laser-processing heads using the tool changer also enables automated change over between different types of laser processing heads, further expanding the breadth of laser processing flexibility in a hybrid CNC. This presentation highlights the development, challenges and future impact of hybrid CNCs on laser processing.

In this paper, a calibrated, fast, multiscale thermal model coupled with a 3D finite element mechanical model is used to simulate residual stress formation and deformations during selective laser melting. The resulting reduction in computation time allows evolutionary algorithm-based optimization of the process. A multilevel optimization strategy is adopted

168

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9738: Laser 3D Manufacturing III

9738-32, Session 12

Femtosecond laser written microresonators and nanophotonic circuitry (Invited Paper) Robert A. Norwood, Khanh Q. Kieu, Gregory A. Cohoon, College of Optical Sciences, The Univ. of Arizona (United States); Babak Amirsolaimani, Soha Namnabat, Jeff Pyun, The Univ. of Arizona (United States) The advent of advanced solid-state lasers, specifically fiber lasers, has ushered in a new era in laser writing. At the same time, multiphoton 3D writing has continued to develop, with new materials with higher contrast and associated secondary properties increasingly available. While modelocked Ti:sapphire lasers have been the workhorse for multiphoton writing systems, the recent development of compact, femtosecond fiber lasers enable turn-key multiphoton lithography systems to be a reality, and provide a route to the creation of sophisticated photonic structures, such as 3D microresonators and integrated nanophotonic circuitry. We present several developments regarding the use of femtosecond lasers for the creation of sophisticated micro- and nanophotonic device structures. We first present the use of a Ti:sapphire laser for the ablative creation of microresonator disks with high quality factors (Q) in optical fiber; the ultra-low loss of optical fiber coupled with simple post-processing result in resonators with Q’s approaching ten million. We then discuss the development of modelocked femtosecond fiber laser-based systems for nanophotonic circuit writing, primarily in a three-photon modality. The modelocked fiber laser at the heart of this system is hand-held and relies on a novel tapered fiber-based carbon nanotube saturable absorber for modelocking, and the three-photon modality increases the options for resist materials significantly, compared to the two-photon case, owing to parity spectroscopic selection rules. Finally we discuss associated writable optical polymer material advances, some of which have potential for applications in the mid-infrared.

9738-34, Session 12

Inkjet printed 3D micro- and nanostructures for Phased Array Antenna (Invited Paper) Peter M. Grubb, The Univ. of Texas at Austin (United States); Harish Subbaraman, Omega Optics, Inc. (United States); Ray T. Chen, The Univ. of Texas at Austin (United States) A complete inkjet-printed 3D structure containing 50 Ohm transmission lines, CNT-based FET, switching network and phased array antenna pads are printed in a conformable substrate. Large steering angles and high frequency switching speed of the CNT-based FET are demonstrated which can be used for air-borne and space-borne applications for remote sensing and free space wireless communications.

9738-35, Session 12

Improving resolution of periodic patterns with three-color photolithography Zuleykhan Tomova, John T. Fourkas, Univ. of Maryland, College Park (United States) Novel visible-light-based lithographic techniques have demonstrated high potential in achieving the super resolution of the fabricated features. Nonlinear interaction of light from even a single visible laser beam can lead to the formation of the isolated structures with size of 100 nm or smaller. Different exposure schemes, involving a second light source, allow

Return to Contents

for control of the chemical polymerization reaction. In such approaches, nonlinear absorption from a first laser beam excites molecules to a higher energy state that can produce free radicals and initiate a polymerization reaction. Simultaneous exposure to a second laser beam, typically in continuous wave mode, can prevent polymerization through deactivating molecules from the excited state back to the ground state before they can form free radicals. It is further possible to limit size of the structures by spatially changing the profile of the laser beam to only deactivate excited molecules in selected regions. Even though such two-color lithography has been demonstrated to have the ability to fabricate small isolated features, the two competing chemical processes, deactivation and free-radical formation, that are initiated form the excited state limit its potential for applications that require fabrication of close-packed features. This problem can be avoided by employing a three-color lithography scheme, in which the state that produces free radicals, differ from a state that deactivates molecules. In this work, we have explored various exposure schemes to achieve smallest pitch and spacewidth distance down to 60 nm.

9738-36, Session 12

Continuous liquid interface production (CLIP) (Invited Paper) John Tumbleston, Carbon3D, Inc. (United States) Continuous liquid interface production (CLIP) can rapidly produce 3D parts using a range of polymeric materials. A DLP-based technique, CLIP proceeds via projecting a sequence of UV images through an oxygenpermeable, UV-transparent window below a liquid resin bath. A thin uncured liquid layer, or dead zone, is created above the window and maintains a liquid interface below the advancing part. Above the dead zone, the curing part is drawn out of the resin bath creating suction forces that renew reactive liquid resin. The dead zone is created due to oxygen inhibition of photopolymerization, a process that is traditionally a nuisance in other photopolymerization applications. However, for CLIP oxygen inhibition and creation of the dead zone allows for a continuous mode of printing where UV exposure, resin renewal, and part elevation are conducted simultaneously. This continual process is fundamentally different from traditional bottom-up stereolithography printers where these steps must be conducted in separate and discrete steps. Furthermore, the relatively gentle nature of CLIP due to the established dead zone enables the use of unique materials with a wide range of mechanical properties. This presentation will showcase the CLIP technology and provide a detailed picture of interactions between different resin and process parameters. New applications for 3D printing that span the micro- to macro-scale enabled by CLIP’s combination of unique materials and part production speed will also be presented.

9738-37, Session 12

The application of digital medical 3D printing technology on tumor operation (Invited Paper) Jimin Chen, Beijing Univ. of Technology (China) The surgary doctor makes use of the guide to helps them to operate with 3D printing technology . These printed guide make the operation easy and time saving while operation. In this paper we intruduced an application of 3D printing technology in tumor operation.Currently for tumor treatment main methods are surgery, radiotherapy, chemotherapy. Howeve.traditional radioactive rays kill cancer cells as well as normal tissues. A radioactive seed implantation treatment technology has been introduced to treat tumor. It implants the tiny radioactive seeds into tumor and kill cancer cells only.The problem is to position the seeds in tumor exactly. Traditionally the digital laminography was used frequently during invasive procedure.It is expensive and cost time. We use 3D printing to print guide for this operation.Method puncture needle - localization guided by printed guide was performed in face tumors and prepared for operation. It is concluded that the new type guide is dominantly advantageous.

+1 360 676 3290 · [email protected]

169

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII Monday - Tuesday 15–16 February 2016 Part of Proceedings of SPIE Vol. 9739 Free-Space Laser Communication and Atmospheric Propagation XXVIII

9739-1, Session 1

9739-2, Session 1

Alphasat-Sentinel-1A optical inter-satellite links: run-up for the European data relay satellite system

In-orbit verification of small optical transponder (SOTA): Evaluation of satellite-to-ground laser communication links (Invited Paper)

Daniel Troendle, Patricia Martin Pimentel, Christoph Rochow, Herwig Zech, Gerd Muehlnikel, Frank F. Heine, Tesat-Spacecom GmbH & Co. KG (Germany); Rolf Meyer, Sabine D. Philipp-May, Michael Lutzer, Deutsches Zentrum für Luft- und Raumfahrt e.V. (Germany); Edoardo Benzi, Philippe Sivac, Silvia Mezzasoma, Harald Hauschildt, Mike Krassenburg, European Space Research and Technology Ctr. (Netherlands); Ian Shurmer, European Space Research and Technology Ctr. (Germany) Laser Communication Links in Orbit have become routine for Alphasat TDP1 GEO data relay and the Sentinel-1A LEO satellite. The Laser Communication Terminals (LCTs) onboard both satellites provide optical LEO-GEO communication links at data rates up to 1.8 Gbps, with a design that could scale up to 7.2 Gbps in the future. In November 2014, the first optical link between both satellites was established. Since then, a large number of links have been performed with both quasi-operational and experimental character. The campaign has demonstrated stable and bit-error free links over LEO-GEO distances of up to 45’000km with optical transmit power of only 1.1W. With a system requirement of BER30 kg) and power (>100 W) requirements that are well beyond the limits of CubeSats. Eliminating the mechanical gimbal and implementing bodypointing of the laser enables a significantly smaller, lighter optical terminal. This approach takes advantage of the exceptionally low moments of inertia of CubeSats and their ability to perform rapid slew maneuvers.

9739-7, Session 2

The lunar laser communication demonstration time-of-flight measurement system: overview, on-orbit performance and ranging analysis Mark L. Stevens, Ronald R. Parenti, Matthew M. Willis, Joseph A. Greco, Farzana I. Khatri, Bryan S. Robinson, Don M. Boroson, MIT Lincoln Lab. (United States) The Lunar Laser Communication Demonstration (LLCD) which flew on the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission achieved record uplink and downlink communication data rates between an earth-based ground terminal and a satellite orbiting the moon. In addition, the high-speed clocks of the communication system were used to accurately measure the round-trip time-of-flight (TOF) of signals sent to the moon and back to the Earth. The measured TOF data, sampled at a 20 kS/s rate, and converted to distance has been processed to show a Gaussian white noise floor typically less than 1 cm RMS. This resulted in a precision for relative

+1 360 676 3290 · [email protected]

171

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII distance measurements more than two orders of magnitude finer than the RF-based navigation and ranging systems used during the LADEE mission. This paper presents an overview of the TOF system and processing used in the experiment, a summary of the on-orbit measurements, and an analysis of the accuracy of the measured data for the mission. The mission data was collected and stored for off-line processing. But with specialized designs, future systems could perform in-situ real-time TOF calculations and data processing whenever a bi-directional lasercom link is established.

9739-8, Session 2

Telecom and scintillation first data analysis for DOMINO: laser communication between SOTA, onboard SOCRATES satellite, and MEO optical ground station (Invited Paper) Duy-Ha Phung, Etienne Samain, Nicolas Maurice, Dominique Albanesse, Hervé Mariey, Mourad Aimar, Gregoire Martinot-Lagarde, Observatoire de la Côte d’Azur (France); Géraldine Artaud, Jean-Luc Issler, 3SNES French Space Agency (France); Nicolas Vedrenne, MarieTherese Velluet, ONERA, French Aerospace Lab (France); Morio Toyoshima, Maki Akioka, Dimitar Kolev, Yasushi Munemasa, Hideki Takenada, Naohiko Iwakiri <[email protected]>, NICT - Japanese National Institute of Information and Communication Technologies (Japan) The DOMINO project (Demonstrator for Optical teleMetry at hIgh data rate iN low earth Orbit) is conducted in collaboration between the French national center for space studies (CNES), the Cote d’Azur observatory (Geoazur ? OCA), ONERA and the National Institute of Information and Communications Technology (NICT). Geoazur is the project general contractor. DOMINO project aims to demonstrate the feasibility of a free-space optical communication link between SOTA (Small Optical TrAnsponder), [1], [2], onboard SOCRATES microsatellite (launched on May 24, 2014), and the MeO station, [3], located at Caussols, France. The main challenges of the project are the implementation of a complete laser communication from space to ground and the characterization of the turbulent atmosphere during the optical data transfer. The optical link between the SOCRATES satellite and the Meo Optical Ground Station (OGS) has been successfully established for all of 4 scheduled passes on June 22, 23, 28 (10 Mbps at 1549 nm) and July 21 (10 Mbps at 976 nm). During these passes, the average optical power, telecom signal and bit error rate have been continuously recorded at Meo OGS with different pupils (1.5 m, 0.4 m and 0.2 m diameter). In the presentation, we will first describe the Nasmyth optical bench with our monopixel ? detector for the scintillation and telecom signals measurements and then present some results of telecom and scintillation data analysis

9739-9, Session 3

A new approach for delivering extremely large volumes of data from LEO to ground Bryan S. Robinson, Curt M. Schieler, Don M. Boroson, MIT Lincoln Lab. (United States) No Abstract Available

172

9739-10, Session 3

Overview of Ground Station 1 supporting the NASA Laser Communications Relay Demonstration Project William T. Roberts, Jet Propulsion Lab. (United States) and California Institute of Technology (United States); Sabino Piazzolla, Thang Trinh, Vachik Garkanian, Lewis C. Roberts, Malcolm W. Wright, Ryan Rogalin, Janet P. Wu, Loren P. Clare, Arvid P. Croonquist, Jet Propulsion Lab. (United States) Optical Ground Station 1 (OGS1) is the first of a new breed of dedicated ground terminals to support NASA’s developing space-based optical communications infrastructure. It is based at NASA’s Optical Communications Telescope Laboratory (OCTL) at the Table Mountain Observatory near Wrightwood, CA. The system will serve as the primary ground station for NASA’s Laser Communications Relay Demonstration (LCRD) experiment. This paper presents an overview of the OCTL telescope facility, the OGS1 ground-based optical communications systems, and the networking and control infrastructure currently under development. The OGS1 laser safety systems and atmospheric monitoring systems are also described.

9739-11, Session 3

Laser communication relay demonstration Eduard Y. Luzhanskiy, David Israel, Bernard Edwards, NASA Goddard Space Flight Ctr. (United States) NASA is presently developing first all optical high data rate satellite relay system, LCRD. To be flown on commercial geosynchronous satellite, it will communicate at DPSK and PPM modulation formats up to 1.244 Gbps. LCRD flight payload is being developed by NASA’s Goddard Space Flight Center. The two ground stations, one on Table Mountain in CA, developed by NASA’s Jet Propulsion Laboratory and another on the Hawaiian island will enable bi-directional relay operation and ground sites diversity experiments. In this paper we will report on the current state of LCRD system development, planned operational scenarios and expected system performance.

9739-12, Session 3

Overview of optical data relay system in JAXA (Invited Paper) Yoshikazu Chishiki, Shiro Yamakawa, Yutaka Takano, Yuko Miyamoto, Tomohiro Araki, Hiroki Kohata, Japan Aerospace Exploration Agency (Japan) To meet increasing demands of high-speed data transmission, JAXA has started to develop a new optical data relay system. This system provides 1.8Gbit/s data relay service through optical inter-satellite link and Ka-band feeder link using a data relay satellite equipped with an optical terminal. Target launch year of the optical data relay satellite is 2019 in Japanese fiscal year, and another optical terminal for LEO satellite and Ka-band ground stations are developed together. This paper describes the development plan and the technologies of the optical data relay system.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII

9739-13, Session 4

Adaptive optics for high data rate satellite to ground laser link Nicolas Vedrenne, Jean-Marc Conan, Cyril Petit, Vincent Michau, ONERA (France) To match the increasing need for high data rate between high altitude platforms and ground stations, Adaptive Optics for free space optics is investigated. Part of the interest is motivated by the need for coupling the received wave into a single mode fiber, to reap the benefits of the technological maturity of the fibered components. The Adaptive Optics correction must be effective in various conditions, sometimes unfavorable, i.e. in sites where atmospheric turbulence is strong, or with LEO satellites at potentially very low elevations. In Astronomy, the performance of Adaptive Optics is characterized by average quantities such as average Strehl ratio or encircled energy. For free space communications, the fluctuation of the injection efficiency, with AO compensation, has to be statistically studied as well. It is investigated here for both links LEO-to-ground and GEO-toground.

9739-14, Session 4

Multi-spots with MEMS deformable mirrors for laser guide star in astronomy Franck Marchis, Iris AO, Inc. (United States) and SETI Institute (United States); Romain Fetick, SETI Institute (United States); Daniel Asoubar, Christian Hellman, LightTrans International UG (Germany); Thierry Fusco, ONERA (France) We present a method to improve the beam quality of an outgoing sodium laser guide star beam, and also to create atmospheric multi-spots and complex shapes suitable for optimal adaptive optics corrections. A segmented MEMS deformable mirror controlled by 111 actuators is inserted in the beam of the laser to actively control the wavefront of the laser guide star in tip-tilt and also in piston. After calculating the optimal tip-tilt positions of each segment to reproduce a desired shape, we can reduce the effect of non-destructive and destructive interferences by modulating the segments in piston in random position up to a few kHz. The propagation through the instrument and the atmosphere was carefully simulated using Virtual Lab and also our own Matlab-based code. Our simulation has been run to match the VLT’s laser guide star facilities. Such a simulation shows that the segmented MEMS Mirror can easily be inserted into an existing LGS optical system, there is consequently no need to create a dedicated or expensive optical system for the use of our method. An optical setup was used to validate the method in a lab. We will discuss future applications of the beam splitting method for astronomy, as well as telecommunication and industrial applications.

9739-15, Session 4

Two-axis gimbal for stratospheric air-to-air and air-to-ground laser communication Amnon G. Talmor, Facebook, Inc. (United States) For links to/from high-altitude-platforms and between such platforms, a hemispherical two-axis gimbal with + 30? filed-of-regard and low aerodynamic drag has been designed. The design is based on is based on the Coude path, and is mechanically robust over +60?C to -80?C. Its mass is under 3Kg, including the optics bench that houses a fast steering mirror. The design has been manifested onboard a carbon fiber and magnesium structure, motorized by permanent magnet motors, commutated by optical encoders, electrically connected via rotary slip-rings, rotationally aligned

Return to Contents

by thin ceramic-on-steel bearings, and controlled by embedded electronics aboard rigid-flex architecture.

9739-16, Session 5

A burst-mode photon-counting receiver with automatic channel estimation and bit rate detection Hemonth G. Rao, Catherine DeVoe, Andrew S. Fletcher, Igor Gaschits, Farhad Hakimi, Scott A. Hamilton, Nicholas D. Hardy, John Ingwersen, Rich D. Kaminsky, John D. Moores, Marvin S. Scheinbart, Timothy M. Yarnall, MIT Lincoln Lab. (United States) No Abstract Available

9739-17, Session 5

Propagation modeling results for narrowbeam undersea laser communications Andrew S. Fletcher, Nicholas D. Hardy, Scott A. Hamilton, MIT Lincoln Lab. (United States) No Abstract Available

9739-43, Session 5

Free-space optical communications using encoding of data on different orbitalangular-momentum modes Asher J. Willner, Yongxiong Ren, Guodong Xie, Long Li, Yinwen Cao, Zhe Zhao, Peicheng Liao, Zhe Wang, Yan Yan, Nisar Ahmed, Cong Liu, The Univ. of Southern California (United States); Moshe Tur, Tel Aviv Univ. (Israel); Alan E. Willner, The Univ. of Southern California (United States) Free-space optical communications can play a significant role in line-ofsight links. In general, data can be encoded on the amplitude, phase, or temporal position of the optical wave. Importantly, there are environments for which ever-more information is desired for a given amount of optical energy. This can be accomplished if there are more degrees-of-freedom that the wave can occupy to provide higher energy efficiency for a given capacity (i.e., bits/photon). Traditionally, free-space optical links have used only a single beam, such that there was little opportunity for a wave to occupy more than one spatial location, thereby not allowing the spatial domain to be used for data encoding. Recently, space- and mode-multiplexing has been demonstrated to simultaneously transmit multiple data-carrying free-space beams. Each spatially overlapping mode was orthogonal to other modes and carried a unique amount of orbital-angular-momentum (OAM). In this paper, we consider that OAM modes could be a data-encoding domain, such that a beam could uniquely occupy one of many modes, i.e., 4 modes would provide 4 possible states and double the bits of information for the same amount of energy. In the past, such OAM-based encoding was shown at kHz data rates. We will present the architecture and experimental results for OAM-based data encoding for a free-space 1.55- ?m data link under different system parameters. Key features of the results include: (a) encoding on several modes is accomplished using a fast switch, and (b) low bit-error-rates are achieved at >Gbit/s, which is orders-of-magnitude faster than previous results.

+1 360 676 3290 · [email protected]

173

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII

9739-18, Session 6

Innovative free space optical communication and navigation system with high data rate communication, precision ranging, range rate measurements, and accurate spacecraft pointing Guangning Yang, NASA Goddard Space Flight Ctr. (United States); wei lu, xiaoli sun, Jeffrey chen, Michael Krainak, NASA Goddard Space Flight Ctr (United States) We report an Innovative Free Space Optical Communication and Navigation System which provides high data rate communication, precise measurements of spacecraft ranging, range rate, and accurate spacecraft pointing. A complete breadboard system was built. It includes both space and ground terminals. Along with 622MBPS data link, the following performances are achieved: two way ranging with 20um ranging and 10um/s range rate accuracy. This is accomplished through the Doppler frequency and data clock phase measurement. This system opens a new way for science missions such as precision formation flight to measure the variation of the gravity field due to motions within the atmosphere, oceans, and solid body of different planetary bodies. It also establishes an integrated service platform for optical navigation, which provides both communication and precision spacecraft ranging and range rate measurements, as well as the accurate spacecraft pointing.

9739-19, Session 6

Gigabit per second modulation and transmission of a partially coherent beam through laboratory turbulence Anatoly Efimov, Los Alamos National Lab. (United States) Numerous theoretical and not so numerous experimental works consistently prove that the performance of partially coherent beams (PCB) in free-space optical communication systems would surpass that of a fully coherent beam. This is because the scintillations of the PCB are typically lower than those of a coherent beam under appropriate selection of beam aperture and coherence radius. It was long believed, however, that partially coherent beams are difficult to modulate with data at high rates in the Gbps range. This misconception is rooted in the practice of generating PCBs using rotating diffusers or SLM masks, which are inherently slow. An alternative method to generate PCBs involves simply coupling a reasonably, but not excessively, broadband light source into a short piece of multimode fiber. By placing the standard LNBO modulator between the source and the fiber we demonstrate straightforward OOK modulation of the PCB at 1 Gbps, limited only by our electronics hardware. We propagate the modulated PCB through a laboratory turbulence and measure resulting eye diagrams and compare them to those obtained with a coherent beam modulated in the same way. The quality of the PCB eyes is much better than those of the coherent beam as expected from a separate set of scintillation measurements. This simple experiment demonstrates the feasibility of PCBs for high-data rate free-space optical communication.

L. Murphy, Christopher I. Moore, U.S. Naval Research Lab. (United States) The performance of free space optical (FSO) communication systems is strongly affected by optical scintillation. Scintillation fades causes can cause errors when the power on a detector falls below its noise floor, while surges can overload a detector. The very long time scale of scintillation compared to a typical bit in an FSO link means that error-correcting protocols designed for fiber optic links are inappropriate for FSO links. Comparing the performance effects of different components, such as photodetectors, or protocols, such as FEC, in the field is difficult because conditions are constantly changing. On the other hand laboratory-based turbulence simulators, often using hot plates and fans, do not really simulate the effects of long-range propagation through the atmosphere. We have investigated a different approach. Scintillation has been measured during field tests using FSO terminals by sending a cw beam through the atmosphere. A high dynamic range photodetector was digitized at a 5 KHz rate and files of the intensity variations were saved. Many hours of scintillation data under different environmental conditions and at different sites have been combined into a library of data. A fiber-optic based scintillation playback system was then used in the laboratory to test modems and protocols with the recorded files. This allowed comparisons using the same atmospheric conditions allowing optimization of such parameters as detector dynamic range. It also allowed comparison and optimization of different error correcting protocols.

9739-21, Session 6

Demonstration of lasercom and spatial tracking in the near infra red with a silicon Geiger-mode APD array Timothy M. Yarnall, MIT Lincoln Lab. (United States); Benjamin W. Horkley, MIT Lincoln Lab. (United States) and Massachusetts Institute of Technology (United States); Ajay S. Garg, Scott A. Hamilton, MIT Lincoln Lab. (United States) We present a demonstration of a high-rate photon counting receiver and spatial tracker based on a silicon Geiger-mode avalanche photodiode array (GM-APD). This array enables sensitive high-rate optical communication in the visible and near infra red regions of the spectrum. The single photon response of the Geiger-mode detection process permits each array element to act as a photon counting receiver thereby providing sensitivity that approaches Shannon capacity limits for on-off keying and 16-ary pulse position modulation with strong error correction coding. The array contains 1024 elements arranged in a 32x32 pixel square. This large number of elements supports high data rates through the mitigation of blocking losses and associated data rate limitations created by the reset time of an individual Geiger-mode detector. Additionally, the array records the spatial coordinates of each detection event. By computing the centroid of the distribution of spatial detections it is possible to determine the angle-ofarrival of the detected photons. We demonstrate tracking of faint optical signals, sufficient to support links through a variety random media that introduce wavefront tilt. These levels of performance imply that Si GM-APD arrays are excellent candidates for a variety free space lasercom applications ranging from atmospheric communication in the 1 micron or 780 nm spectral windows to underwater communication in the 480 nm to 520 nm spectral window.

9739-20, Session 6

Characterization of modems and error correcting protocols using a scintillation playback system

9739-22, Session 7

William S. Rabinovich, Rita Mahon, Mike S. Ferraro, James

Sylvain Poulenard, Airbus Defence and Space SAS

174

Optical links sizing for future broadband geostationary satellite feeder

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII (France); Jean-Marc Conan, ONERA (France); Bernard Roy, Airbus Defence and Space SAS (France); Angélique Rissons, Institut Supérieur de l’Aéronautique et de l’Espace (France) The main requirements for the next-generation of high throughput geostationary satellites are an annual link availability of 99.9%, a capacity around one Terabits/s and to be bent-pipe. An optical link, based on wavelength division multiplexing at 1.55µm, is a valuable alternative to overcome the limited data rata and the interference issues of conventional radio-frequencies. However, compared to RF links, optical links are much more sensitive to atmospheric effects such as cloud coverage and optical turbulence leading to important signal attenuation. In this study, cloud obstruction is avoided thanks to a network of geographically spread optical ground stations connected to terrestrial fiber network. Concerning atmospheric turbulence, mitigation techniques are investigated to maximize the optical link budgets. For the downlink, power losses induced by the coupling of the optical signal into the single mode fiber of the receiver optical pre-amplifier are reduced by a fine pointing mirror that centers in real-time the intensity distribution in the core of the fiber. The uplink beam is pre-compensated with the same mirror to reduce the turbulence-induced pointing errors. The performance of such pre-compensation is derived by considering the decorrelation of the perturbations between the uplink and downlink directions that are separated by the pointing ahead angle. Eventually, the achieved optical data rates in NRZ-DPSK are derived from the optical link budgets. We conclude that the described transparent optical feeder link system has a capacity ~600Gbps with an annual availability of 99.9%. Solutions are proposed to easily increase this capacity to one Terabit/s.

9739-23, Session 7

Architectural and operational considerations emerging from hybrid RFoptical network loading simulations Yijiang Chen, Douglas S. Abraham, David P. Heckman, Andrew Kwok, Bruce E. MacNeal, Kristy Tran, Janet P. Wu, Jet Propulsion Lab. (United States) A technology demonstration of free space optical communication at interplanetary distances is planned via one or more future NASA deepspace missions. Such demonstrations will “pave the way” for operational use of optical communications on future robotic missions with science payloads that generate large data volumes (e.g. synthetic aperture radar, hyperspectral imagers, large-pixel-area imagers, etc.). Human exploration missions to distant lunar orbits, asteroids, and Mars will also benefit from the large data volumes achievable with optical communications. Such optical communications capability will augment existing RF communications capability. Hence, the Deep Space Network (DSN) architecture will need to evolve in a manner that accommodates RF-only, combined-RF-and-optical, and optical-only missions. Preliminary attempts to model the anticipated future mission set and simulate how well it loads onto assumed architectures with combinations of RF and optical apertures have been evaluated. The evaluation reveals a number of potential architectural and operational trades between mission and ground infrastructure elements that continue to be studied. This paper discusses the results of preliminary loading simulations for hybrid RF-optical network architectures and highlight key mission and ground infrastructure considerations that emerge.

9739-24, Session 7

Deep space laser communications Abhijit Biswas, Joseph M. Kovalik, Meera Srinivasan, Malcolm W. Wright, William H. Farr, Jet Propulsion Lab.

Return to Contents

(United States) The paper will provide a brief introduction with literature survey of past and ongoing deep-space laser communications studies and programs. The key technology challenges will be enumerated that include: (i) acquisition tracking and pointing from deep-space ranges where Earth-ground-based transmitted laser beacon irradiances are weak and (ii) photon-efficient communications due the faint signal received and (iii) additive background noise at both ends of the link due to long durations of operating at shallow solar separation angles. The current strategies being pursued for mitigating these challenges will then be discussed and some examples of progress achieved so far will be reported. Studies related laser communication from the outer reaches of the solar system and inter-stellar space will be touched upon, Finally, a few examples of light science applications that advanced laser communication technologies can bring to bear will be described.

9739-25, Session 8

Two dimensional thermo-optic beam steering using a silicon photonic optical phased array Rita Mahon, William S. Rabinovich, Peter G. Goetz, Marcel W. Preussner, Mike S. Ferraro, James L. Murphy, U.S. Naval Research Lab. (United States) Components for free space optical communication terminals such as lasers, amplifiers, and receivers have all shrunk in both size and power consumption over the past several decades. However, pointing systems, such as fast steering mirrors and gimbals, have remained large and power-hungry. Optical phased arrays provide a possible solution for non-mechanical beam steering that can be compact and lower in power. Silicon Photonics is a promising technology for phased arrays because it has the potential to scale to many elements and has compatibility with CMOS fabrication. For most free space optical communication applications, two-dimensional beam steering is needed. To date, Silicon photonic phased arrays have achieved two-dimensional steering by combining thermo-optic steering with wavelength tuning and an output grating. This architecture does not work for the receive function of an FSO link. We demonstrate steering using the thermo-optic effect for both dimensions.

9739-26, Session 8

Impact ionization engineered avalanche photodiode arrays for free space optical communication Mike S. Ferraro, William S. Rabinovich, Rita Mahon, U.S. Naval Research Lab. (United States) High sensitivity photodetectors serve two purposes in free space optical communication: data reception and position sensing for pointing, tracking, and stabilization. Because of conflicting performance criteria, two separate detectors are traditionally utilized to perform these tasks but recent advances in the fabrication and development of large area, low noise avalanche photodiode (APD) arrays have enabled these devices to be used both as position sensitive detectors (PSD) and as communications receivers. Combining these functionalities allows for more flexibility and simplicity in optical assembly design without sacrificing the sensitivity and bandwidth performance of smaller, single element data receivers. Beyond eliminating the need to separate the return beam into two separate paths, these devices enable implementation of adaptive approaches to compensate for focal plane beam wander and breakup often seen in highly scintillated terrestrial and maritime optical links. While the Naval Research Laboratory and Optogration Inc, have recently demonstrated the performance of single period, InAlAs/InGaAs APD arrays as combined data reception and tracking sensors, an impact ionization engineered (I2E) epilayer design

+1 360 676 3290 · [email protected]

175

Conference 9739: Free-Space Laser Communication and Atmospheric Propagation XXVIII achieves even lower carrier ionization ratios by incorporating multiple multiplication periods engineered to suppress lower ionization rate carriers while enhancing the higher ionization rate carriers of interest. This work presents a three period I2E concentric, five element avalanche photodiode array rated for bandwidths beyond 1GHz with measured carrier ionization ratios of 0.05-0.1 at moderate APD gains. The epilayer design of the device will be discussed along with initial device characterization and high speed performance measurements.

9739-27, Session 8

Novel photon-counting detectors for freespace communication Michael A. Krainak, Guangning Yang, Xiaoli Sun, NASA Goddard Space Flight Ctr. (United States); Wei Lu, ASRC Federal Space and Defense (United States); Scott Merritt, NASA Goddard Space Flight Ctr. (United States); Jeff Beck, DRS Technologies, Inc. (United States) We present performance data for novel photon counting detectors for free space optical communication. NASA GSFC is testing the performance of three novel photon counting detectors 1) a 2x8 mercury cadmium telluride (HgCdTe) avalanche array made by DRS Inc... 2) a commercial 2880 silicon avalanche photodiode array and 3) a prototype resonant cavity silicon avalanche photodiode array. We will present and compare dark count, photon detection efficiency, wavelength response and communication performance data for these detectors. We discuss system wavelength trades and architectures for optimizing overall communication link sensitivity, data rate and cost performance. The HgCdTe APD array has photon detection efficiencies of greater than 50% were routinely demonstrated across 5 arrays, with one array reaching a maximum PDE of 70%. High resolution pixel-surface spot scans were performed and the junction diameters of the diodes were measured. The junction diameter was decreased from 31 ?m to 25 ?m resulting in a 2x increase in e-APD gain from 470 on the 2010 array to 1100 on the array delivered to NASA GSFC. Mean single photon SNR’s of over 12 were demonstrated at excess noise factors of 1.2-1.3. The commercial silicon APD array has a fast output with rise times of 300ps and pulse widths of 600ps. Received and filtered signals from the entire array are multiplexed onto this single fast output. The prototype resonant cavity silicon APD array is being developed for use at 1 micron wavelength.

9739-28, Session 9

AlGaInN laser diode technology for freespace and plastic optical fibre telecom applications Stephen P. Najda, Piotr Perlin, Tadek Suski, Lucja Marona, Michal Bockowski, Mike Leszczynski, Przemek Wisniewski, Robert Czernecki, TopGaN Ltd. (Poland); Robert Kucharski, Ammono S.A. (Poland); G. Targowski, LopGaN Ltd. (Poland); Scott Watson, Anthony E. Kelly, Univ. of Glasgow (United Kingdom); Malcolm A. Watson, Paul M. Blanchard, Henry J. White, BAE Systems (United Kingdom) The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. We consider the suitability of AlGaInN laser diode technology for free space laser communication, both airborne links and underwater telecom applications. We measure visible light (free-space and underwater) communications

176

at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Gallium-nitride (GaN) blue laser diode with single longditudinal mode operation. In addition, we measure Gbit/s data transmission for AlGaInN laser diodes in plastic optical fibre (POF).

9739-29, Session 9

Development, testing and initial space qualification of 1.5-µm, high-power (6W), pulse-position-modulated (PPM) fiber laser transmitter for deep-space laser communication Shantanu Gupta, Doruk Engin, Dave Pachowicz, JeanLuc Fouron, Juan Lander, Xung Dang, Slava Litvinovich, Ti Chuang, Kent Puffenberger, Frank Kimpel, Rich Utano, Fibertek, Inc. (United States); Malcolm W. Wright, Jet Propulsion Lab. (United States) Recent space lasercom demonstrations ? NASA LLCD mission and TeSat’s GEO crosslink demonstration, point to the tremendous potential for space laser communication in providing high data-rate links for various NASA exploration missions. Increased bandwidth and increased ranges for asteroid and inter-planetary links require low SWaP, high power, laser transmitters. For such photon-starved space optical links, a flexible format pulseposition-modulation (PPM) scheme provides high bits/energy efficiency. We have developed a compact (10”x8”x2.4”, 7.5 lbs) and sealed, 1.5-um, polarization-maintaining, fiber laser transmitter sub-system, operating to PPM-128 format at up to 6W for pulse slots from 0.5 to 8-nsec, with peak powers reaching 1 kW. An athermal design (only passive cooling) ensures high wall-plug efficiency (~15%). Functional testing has been completed for PPM formats ranging from PPM-16 to PPM-128, with pulse slots of 0.5, 1, 2, 4, and 8-nsec. Critical parameters such as extinction ratio is measured >33-dB, polarization extinction >15-dB, spectral line-width 100 nJ allows for a NOPO output power of up to 600 mW @ 50 MHz with a transform-limited pulse duration around 100 fs.

9740-25, Session 6

Development of a kilowatt-class, joulelevel ultrafast laser for driving compact high average power coherent EUV / soft x-ray sources Brendan Reagan, XUV Lasers (United States) and Colorado State Univ. (United States); Cory Baumgarten, Michael Pedicone, Colorado State Univ. (United States); Herman Bravo, XUV Lasers (United States); Liang Yin, Colorado State Univ. (United States); Mark Woolston, XUV Lasers (United States) and Colorado State Univ. (United States); Hanchen Wang, Colorado State Univ. (United States); Carmen S. Menoni, XUV Lasers (United States) and Colorado State Univ. (United States); Jorge Rocca, Colorado State Univ. (United States) and XUV Lasers (United States) Our recent progress in the development of high energy / high average power, chirped pulse amplification laser systems based on diode-pumped Yb:YAG amplifiers will be presented, including the demonstration of a laser that produces 1 Joule, sub-10 picosecond duration, ? = 1.03?m pulses at 500 Hz repetition rate. This compact, all-diode-pumped laser combines a mode-locked Yb:KYW oscillator and a water-cooled Yb:YAG preamplifer with two cryogenic power amplification stages to produce 1.5 Joule pulses with high beam quality which are subsequently compressed. This laser system, including pump lasers and optics and the in-vacuum dielectric grating pulse compressor, occupies an optical table area of less than 1.5x3 m^2. The high cooling-capacity cryogenic amplifier heads have a versatile modular design that allows the generation of a variety of pulse energies, repetition rates, and pulse durations depending on the application as well as scaling to higher peak and average power. This laser was employed to pump plasma-based soft x-ray lasers at ? = 10-20 nm at repetition rates >100 Hz. To accomplish this, temporally-shaped pulses were focused at grazing incidence into a high aspect ratio line focus using cylindrical optics on a high shot capacity rotating metal target. This results in an elongated plasma amplifier that produces microjoule pulses at several selectable and narrowlinewidth EUV wavelengths between ? = 109 Å and 189 Å. The resulting 0.2 mW average power in a transition of Ni-like molybdenum at 189 Å is the highest reported from a compact laser source these wavelengths.

9740-26, Session 6

High power and high energy femtosecond lasers based on hybrid architectures Clemens Hönninger, Julien Pouysegur, Birgit Weichelt, Martin Delaigue, Guillaume Machinet, Franck Morin, Florent Guichard, Yoann Zaouter, Amplitude Systèmes (France); Marc Hanna, Frédéric Druon, Patrick Georges, Lab. Charles Fabry (France); Eric Mottay, Amplitude Systèmes (France)

+1 360 676 3290 · [email protected]

187

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI Hybrid architectures based on the combination of fiber- and crystal-based building blocks are powerful configurations for the realization of high average power and high energy femtosecond lasers. These kind of laser architectures combine the advantages of both technologies: simplicity of integration and fabrication of fiber seeders and power and energy extraction capability of crystal-based booster amplifiers. The frontier between the two technologies can be floating and set on at different levels of average power and pulse energy, depending on the targeted requirements. Several applications require high average power at the 100-W level at moderate pulse energies around 100 µJ and pulse repetition rates on the MHz-level. Other applications require the same average power at higher energy levels in the mJ range and lower pulse repetition rates. Hybrid laser architectures are ideally suited to match to both requirements. In this paper, we present hybrid femtosecond lasers with pulse durations around 500 fs, average powers of 100 W, and pulse energies up to several mJ. Repetition rates reach from the 100-kHz-level to multi-MHz.

Glass processing using ultrashort laser pulses: free carrier dynamics and the role of different decay channels Klaus Bergner, Friedrich-Schiller-Univ. Jena (Germany); Malte Kumkar, TRUMPF Laser- und Systemtechnik GmbH (Germany); Andreas Tünnermann, Friedrich-Schiller-Univ. Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany); Stefan Nolte, Friedrich-Schiller-Univ. Jena (Germany) and FraunhoferInstitut für Angewandte Optik und Feinmechanik (Germany) I would like to participate in the student competition.

9740-27, Session 6

Non-infrared femtosecond lasers: status and prospects Max Kahmann, Raphael Gebs, Robert Fleischhaker, Ivo Zawischa, Jochen Kleinbauer, Simone Russ, Lara Bauer, Uwe Keller, Birgit Faisst, Aleksander Budnicki, Dirk Sutter, TRUMPF GmbH & Co. KG (Germany) The unique properties of ultrafast laser pulses with their low thermal influence pave the way to numerous novel applications. Particularly lasers in the sub-pico second regime, so called femtosecond lasers, achieved in the last decade an industrial ready reliability and regain an increasing recognition since these pulse durations combine the advantages of ultrashort pulses with higher efficiency especially for metals. However nowadays for some micro processing applications the infrared wavelength of these lasers is more and more a limiting factor. Thus the next generation of ultrafast industrial lasers have to enable the combination of the advantages of femtosecond pulses and shorter wavelength in order to enter the next stage in terms of precision as smaller focal spot size can be and better surface quality can be achieved. Further the higher photon energy of the shorter wavelength can open a low fluence regime for relevant applications in particular for metals, which is not accessible by infrared light, opening a wide range of opportunities.

9740-28, Session 7

Ultrafast laser micro- and nanoprocessing of dielectrics with Bessel beams (Invited Paper) François Courvoisier, Rémi Meyer, Ludovic Rapp, Ismail Ouadghiri Idrissi, Remo Giust, Pierre-Ambroise Lacourt, Luc Froehly, Luca Fufaro, Maxime Jacquot, John M. Dudley, FEMTO-ST (France) Bessel beams provide a novel route for ultrafast laser processing of solid dielectrics. This is because even at high intensity, they do not undergo nonlinear distortions and allow uniform energy deposition along the beam path. We will review benefits of Bessel -like beams for laser micro and nano-structuring of transparent materials with high aspect ratio: glass and sapphire cutting, high aspect ratio void formation. Of particular interest is the impact of the transverse beam shape and polarization on the control of stress and cracks in glass and sapphire, leading to cleavage after single pass illumination. The research leading to these results, has received funding from the European Union Seventh Framework Programme [ICT-2013.3.2- Photonics] under grant agreement n°619177, project TiSa-TD.

188

9740-29, Session 7

Ultrashort laser pulses offer several possibilities in glass processing, like induction of nanogratings or local welding. Another promising application is the inscription of disruptions, which can be used as cleaving layers in order to separate glass. Here, different spatial and temporal concepts are required to tailor the laser-matter dynamics. To this end it is necessary to understand the fundamental energy deposition and subsequent evolution of free carrier dynamics. The different decay channels lead to various modifications of the material. Applying single laser shots with 1026nm wavelength, 6ps (FWHM) pulse duration and pulse energies from 25µJ to 200µJ leads to a plasma formation inside the glass species (fused silica, Borofloat 33, Gorilla glass). We analyze the spatio-temporal evolution of free carriers induced by ultrashort laser pulses using a pump-probe setup with high temporal and spatial resolution. The plasma development can be divided into 2 phases, a generation and a decay phase. Electron densities around 1 x 10^20cm-3 in the focal plane and 1 x 10^19cm-3 in front of the focus are generated. The free carriers slowly decay within several 100ps. However, the lower densities in front of the focus can be linked to fast electron heating and various decay stages, like exciton formation and self-trapping. These decay channels mainly lead to structural changes like bond breaking and generation of NBOHCs. On the other hand the high intensities inside the focus lead to a stronger electronphonon coupling resulting in strong disruptions.

9740-30, Session 7

Dash line glass- and sapphire-cutting with high power USP laser John Lopez, Univ. Bordeaux 1 (France) Glass cutting is a subject of high interest for flat panel display and consumer electronics industries. Among laser-based, water jet-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology since this laser technology has the unique capacity to produce highly localized bulk modification owing to non-linear absorption. The cutting using USP lasers could be performed either by full ablation which is slow and generates a lot of dust, by controlled fracture propagation which is slow as well and may lead to path deviation, or by stealth dicing which produces rough sidewalls. The laser treatment is often continuous which is not necessary to perform glass cutting and may lead to overexposure. In this paper we report on single pass glass and sapphire cutting using an USP laser (20W @200kHz or 12W@2MHz), based on controlled fracture propagation or stealth dicing, using dash line laser treatment along the cutting trajectory. In-volume energy deposition was done along the glass thickness owing to a Gaussian or a Bessel beam. The results will be discussed in terms of sidewall profile and roughness, path deviation, rim sharpness, energy dose and feedrate. Dash line treatment enables to tune the energy deposition and to produce the cutting effect but with a narrower

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI heat affected zone, a better sidewall quality and a more accurate trajectory control of the cutting path.

9740-31, Session 7

Controlling ultrafast laser filamentation with spatial light modulator Erden Ertorer, Ehsan Alimohammadian, Dale Gottlieb, Jianzhao Li, Peter Herman, Univ. of Toronto (Canada) Self-guiding of the beam created from laser pulses, which is also called filamentation, occurs as a consequence of the balance between selffocussing by the Kerr effect and defocusing in laser-generated plasma that arises when the high intensity also ionizes the material. By using this phenomenon, laser interaction can be extended over multiple Rayleigh lengths to enable high aspect ratio modifications with fast processing speeds. Other advantages of filament modification includes a small heat affected zone and minimal surface damage or crack generation. Dimensions and the morphology of the filament modified zone are also highly dependent on laser parameters and focusing conditions. As a result of focusing and plasma defocusing cycles, ‘hot’ and ‘cold’ spots cause nonuniformities along the interaction zone with damaged zones alternating with gentle modification zones. Moreover, the energy consumed and deflected by the hot zones reduces the overall interaction length of the filament to yield low aspect ratio modification tracks. In order to overcome these issues, a spatial light modulator (SLM) has been employed to actively rearrange the axial distribution of energy along the propagation axis. Laser filaments have been formed in bulk silica glasses with single and burst-train pulses of various energy from a femtosecond laser with 200 fs pulse duration and 515 nm wavelength. The SLM provided various focusing schemes such as forming multiple foci with controlled power splitting, introducing aberration, elongating the focus along the propagation direction, and forming a Bessel beam. Resulting filament tracks were investigated for their structural uniformity, length, and width and tuned by the SLM with optimized beam shaping to generate highly uniform structures variable from 10 um to 100s of um in length.

9740-32, Session 7

Pulse front control with adaptive optics Patrick S. Salter, Bangshan Sun, Martin J. Booth, Univ. of Oxford (United Kingdom) The focusing of ultrashort laser pulses is extremely important for various processes including multiphoton microscopy, photo-activation for biological studies, and laser fabrication. Adaptive optic elements, such as liquid crystal spatial light modulators or membrane deformable mirrors, are routinely used for the correction of aberrations in these systems, leading to improved resolution and efficiency. In this talk, we address the aspects of aberration correction specific to ultrashort pulses. We demonstrate with results from laser fabrication of transparent materials that adaptive elements used with ultrashort pulses may no longer be considered simply in terms of wavefront modification, but that changes to the incident intensity pulse front can also be important. We develop this principle further to show that a combination of adaptive elements, specifically a deformable mirror and spatial light modulator operated in concert, may be used to engineer pulse fronts (contours of constant intensity in space and time within an ultrashort pulse). By this approach, pulse fronts can be generated which are spatially variant across the beam. The simplest case is to generate a beam with a quadratic time delay in the pulse front from the centre to the edge of the beam. This is an equivalent deformation to the propagation time delay (PTD) introduced to ultrashort pulses by many lenses. Experimental measurements of the temporal profile of a pulse in the expanded beam are backed up by observation of the two-photon fluorescence signal at the focus of an objective lens to illustrate the effect.

Return to Contents

9740-33, Session 7

Femtosecond lasers for machining of transparent, brittle materials: Ablative vs. non-ablative femtosecond laser processing Victor V. Matylitsky, Frank Hendricks, Spectra-Physics (Austria) Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones, e-readers, and tablets, cover glass needs to be cut precisely in various shapes. When an ultrashort laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Furthermore, only ultrashort pulse lasers allow cutting of the chemically strengthened substrates such as XensationTM from Schott AG and Corning® Gorilla® glasses without cracking. In this paper, we describe application of a femtosecond laser for machining of transparent materials by means of ablative and non-ablative laser processing. Ablation technologies will be compared with a newly developed non-ablative femtosecond process, ClearShapeTM, using the Spirit industrial femtosecond laser from Spectra-Physics. While ablative femtosecond processing provides the quality that industrial users demand, processing speed needs to be improved. An optimization method to determine the ideal laser processing parameters for multi-pass ablative material removal will be presented. Developed theoretical model helps to estimate the optimal kerf width and the number of scans in order to achieve the desired throughput. On the other hand, the ClearShape femtosecond process allows machining of transparent, brittle materials such as chemically strengthened glass, unstrengthened glass, and sapphire with highest quality and speed.

9740-34, Session 8

High power parallel ultrashort pulse laser processing (Invited Paper) Arnold Gillner, M. Jüngst, Patrick Gretzki, Martin Reininghaus, Fraunhofer-Institute for Laser Technology (Germany) Ultra-short pulse lasers provide outstanding properties for high precision manufacturing with almost no thermal effects and numerous new micro and nano fabrication solutions [1]. With pulse durations in the picosecond and femtosecond range, the absorbed energy is concentrated in the material to a few nanometers, so that thermal damage to the materials can be avoided. These properties have generated numerous processes in precision machining at solar cells, batteries, injection molding tools and electronic components [2]. However for high speed processing and high productivity the used laser power has to be significantly increased. Currently ultrashort pulsed lasers with powers up to 500 W are available, so that also potential applications for macro processing are obtained, which opens large markets in other than the micro processing field [3]. However, using high power ultrashort pulsed lasers with high repetition rates in the MHz region can cause thermal issues like overheating, melt production and low ablation quality as long certain parameter sets and fluence ranges have been considered. High ablation quality only can be achieved, when the processing fluence is close to the ablation threshold, which requires new processing strategies and innovative system components. Beside ultra high speed scanning using polygon scanners the use of multiple laser beams provide the best and most versatile high power ablation solution. With switchable single beams using a special light modulator or a diffractive optical beam splitter, high ablation rates can be achieved while maintaining the high processing quality of ultra short pulse laser ablation. With this approach a next step up to an all optical manufacturing system can be provided. [1] Du, K., Brüning, S., & Gillner, A,. High power picosecond laser with 400W average power for large scale applications. Paper presented at the

+1 360 676 3290 · [email protected]

189

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI Proceedings of SPIE - the International Society for Optical Engineering, 8244, (2012) [2] Gillner, A., Hartmann, C., & Dohrn, A., High quality micro machining with tailored short and ultra short laser pulses, 3rd Pacific International Conference on Applications of Lasers and Optics, PICALO 2008 Conference Proceedings, 685-690. (2008) [3] Russbueldt, P., Mans, T., Hoffmann, H. D., & Poprawe, R,. Status quo and outlook of power scaling of ultrafast lasers. 29th International Congress on Applications of Lasers and Electro-Optics, ICALEO 2010 - Congress Proceedings, , 103 1226-1234, (2010).

9740-35, Session 8

Ultrafast laser drilling of injector nozzles Eric P. Mottay, Amélie Letan, Clemens Hönninger, Amplitude Systèmes (France); Patrick Thibaut, Posalux SA (Switzerland) Optimizing the drilling process for injector fuel nozzles in automotive industry is one of the key factors to achieve significant improvements in fuel efficiency in the coming year. The quality of the nozzle holes edges, as well as careful optimization of the hole shape, allow to eventually optimise the fuel injection process in order to achieve the highest efficiency. The athermal and high quality nature of the ultrafast laser interaction process makes ultrafast laser drilling a prime candidate for this application. Several challenges need however to be overcome for industrial applications, such as processing speed, optimization of hole shape (zero-taper, inversedtaper, straightness …), as well as backwall protection. We will review in this presentation recent developments in ultrafast laser technologies, including advanced synchronisation modes and beam delivery system. Reducing the processing time requires improvement in laser average power, repetition rate, and operating mode. We will present hybrid ultrafast lasers, with the potential for simultaneously achieving high repetition rate, in the MHz regime, as well as high pulse energy. We will also present recent results obtained with non-normal incidence beams and trepanning heads. We will present examples of laser processing of Gasoline Direct Injectors.

Laser processes and analytics for high power 3D battery materials (Invited Paper) Wilhelm Pfleging, Peter Smyrek, Karlsruhe Institute of Technology (Germany) and Karlsruhe Nano Micro Facility (Germany); Melanie Mangang, Yijing Zheng, Karlsruhe Institute of Technology (Germany); Johannes Pröll, Karlsruhe Institute of Technology (Germany) and Karlsruhe Nano Micro Facility (Germany) Laser processes for cutting, modification and structuring of energy storage materials such as electrodes, separator materials and current collectors have a great potential in order to minimize the fabrication costs and to increase the performance and operational lifetime of high power lithiumion-batteries applicable for stand-alone electric energy storage devices and electric vehicles. Laser direct patterning of battery materials as well as laser-assisted formation of selforganized conical surface structures enable a rather new technical approach in order to adjust 3D surface architectures and porosity of composite electrode materials such as LiCoO2, LiMn2O4, LiFePO4, Li(NiMnCo)O2, and Silicon. The architecture design, the increase of active surface area, and the porosity of electrodes or separator layers can be controlled by laser processes and it was shown that a huge impact on electrolyte wetting, lithium-ion diffusion kinetics, cell life-time and cycling stability can be achieved. In general ultrafast laser processing can be used for precise surface texturing of battery materials. Nevertheless, regarding cost-efficient production also nanosecond laser material processing can be successfully applied for selected types of energy storage materials. A concept for an advanced battery manufacturing including laser materials processing will be presented. For developing an optimized 3D architecture for high power composite thick film electrodes electrochemical analytics and post mortem analytics using laser-induced breakdown spectroscopy were performed. Based on mapping of the local state of charge of composite electrodes, an analytical approach for studying chemical degradation in structured and unstructured lithium-ion batteries will be presented.

9740-38, Session 8

9740-36, Session 8

Analysis of the hole shape evolution in fspulse percussion drilling with bursts Helena Kämmer, Felix Dreisow, Andreas Tünnermann, Stefan Nolte, Friedrich-Schiller-Univ. Jena (Germany) Ultrashort pulse laser processing is a precise technique for contact-free machining of microstructures with high quality and a negligible thermal effect in various materials, with many applications in research and industry, e.g. the drilling of fuel injection nozzles. Despite of many research activities the precise drilling of deep structures is still challenging. The hole shape in the depth is influenced by the previously excavated hole capillary, resulting in decreased drilling rates with increasing depth. Additionally the shape of the hole is not reproducible, even under identical conditions. In particular, the appearance of bulges, indentations, bendings and/or multiple capillaries with different orientations may vary statistically. In this work, we analyze the use burst trains with pico- to nanosecond pulse separation in order to improve drilling efficiency and quality. Silicon serves as sample material for investigating the influence of laser drilling with 1030 nm bursts consisting of 200 fs pulses separated by a time delay between 1ps and 4ns. The deep drilling process is directly imaged from the side using a standard CCD camera and an illumination at 1064 nm, where the silicon sample is transparent. The results are compared to drilling without bursts for different pulse energies. The efficiency of the drilling process, the hole quality, as well as reproducibility of the hole shape are analyzed.

190

9740-37, Session 8

Ultrafast pulse lasers jump to industrial macro applications Martin Griebel, JENOPTIK Automatisierungstechnik GmbH (Germany) Ultrafast Lasers have been proven for several micro applications, e.g. stent cutting, for many years. Within its development of applications Jenoptik has started to use ultrafast lasers in macro applications in the automotive industry. The JenLas D2.fs-lasers with power output control via AOM is an ideal tool for closed loop controlled material processing. Jenoptik enhanced his well established sensor controlled laser weakening process for airbag covers to a new level. The patented process enables new materials using this kind of technology. One of the most sensitive cover materials is genuine leather. As a natural product it is extremely inhomogeneous and sensitive for any type of thermal load. The combination of femtosecond pulse ablation and closed loop control by multiple sensor array opens the door to a new quality level of defined weakening. Due to the fact, that the beam is directed by scanning equipment the process can be split in multiple cycles additionally reducing the local energy input. The development used the 5W model as well as the latest 10W release of JenLas D2.fs and achieved amazing processing speeds which directly fulfilled the requirements of the automotive industry. Having in mind that the average cycle time of automotive processes is about 60s, trials had been done of processing weakening lines in genuine leather of 1.2mm thickness. Parameters had been about 15 cycles with 300mm/s respectively resulting in an average speed of 20mm/s and a cycle time even below 60s. First samples had already given into functional and aging tests and passed successfully.

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI

9740-39, Session 8

Feinmechanik (Germany)

Picosecond and fs lasers for industrial material processing

In this work, we report on the laser ablation of silicon samples using bursts of 200fs pulses at a wavelength of 1030nm. Two different experimental approaches were used to generate bursts starting with the pristine laser pulses at a repetition rate of 60 kHz. A Michelson interferometer-based set-up enabled the generation of bursts with time separation between subpulses from 510ps to 4080ps, while a different set-up consisting of an array of birefringent crystals allowed shorter separations in the range from 0.5ps to 16ps.

Roland M. Mayerhofer, Jürgen Serbin, Fred-Walter Deeg, Rofin-Baasel Lasertechnik GmbH & Co. KG (Germany) Cold laser materials processing using ultra-short pulsed lasers has become one of the most promising new technologies for high-precision cutting, ablation, drilling and marking of almost all types of material, without causing excessive thermal damage to the part. These characteristics have opened up new application areas and materials for laser processing, allowing previously impossible features to be created and also reducing the amount of post-processing required to an absolute minimum, saving time and cost. However, short pulse widths are only one part of the story for industrial manufacturing processes which focus on total costs and maximum productivity and production yield. Like every other production tool, ultrashort pulse lasers have to provide high quality results with maximum reliability. Robustness and global on-site support are vital factors, as well as easy system integration. The presentation will give an overview on requirements on laser parameters derived from ultrafast laser material processing and conceptual options for ps- and fs-lasers. It will also discuss laser features and services turning USP lasers into industrial solutions.

9740-40, Session 9

Engineering model for ultrafast laser microprocessing Eric Audouard, Eric P. Mottay, Amplitude Systèmes (France) We present a simple engineering model to reproduce and predict laser processing with ultrafast pulses. We aim at reaching a good estimate of porcessing parameters in various technical situations (static or dynamic beams, single or multi-pulses). The modes does not investigate the influence of specific laser-matter interaction mechanisms, for instance electonc and lattice temperature evolution. Assuming a non linear ligarithmic response of the materials to ultrafast pulses, each material can be described by two global parameters. As the response to a Gaussian shaped pulse is an hyperbolic shaped crater, analytical results are derived. Typical ablation data evolution with fluence such as crater depth and volume ablation rate repoduces experimental results on a wide range of fluences. Effects of top-hat and gaussian profiles can be compared. Optimal fluences for various processes are presented. Dynamical processing is considered, taking into account pulse response superpostion. Simple technical assumptions allow to predict the effet of beam velocity and non normal incident beams and to obtain key parameters for laser processing, such as conical shapes or processing time. In particular, we apply the model to percussion and trepanning drilling with non normal incident beams.

9740-41, Session 9

Ablation of silicon with bursts of femtosecond laser pulses Caterina Gaudiuso, Univ. degli Studi di Bari Aldo Moro (Italy) and Istituto di Fotonica e Nanotecnologie (Italy); Helena Kämmer, Felix Dreisow, Friedrich-Schiller-Univ. Jena (Germany); Antonio Ancona, CNR-Istituto di Fotonica e Nanotecnologie (Italy); Andreas Tünnermann, Stefan Nolte, Friedrich-Schiller-Univ. Jena (Germany) and Fraunhofer-Institut für Angewandte Optik und

Return to Contents

The ablation thresholds and craters depth achieved with the burst-mode processing have been measured and compared to results obtained with the unsplit pristine pulses of equivalent total fluence. It was found that while the ablation threshold is reduced with increasing number of sub-pulses, irrespective of the time delay within the burst, the ablation depth per sub-pulse as a function of the laser fluence exhibits a different behavior depending on the time separation between sub-pulses. For sub-pulse delays shorter than 4ps, for a given burst energy, the crater becomes shallower the larger the number of sub-pulses in the burst is. In contrast, for time separations longer than 510ps, the ablation depth increases with the number of pulses in the bursts. This different behavior can be ascribed to a change of the laser radiation effective penetration depth.

9740-42, Session 10

Investigation of the breaking strength of ultrashort pulse laser diced thin Si wafers Matthias Domke, Bernadette Egle, FH Vorarlberg (Austria); Gernot Fasching, Marius Bodea, Elisabeth Schwarz, Infineon Technologies Austria AG (Austria) High power electronic chips are fabricated on 50 µm thin Si wafers to improve heat dissipation. At these chip thicknesses mechanical dicing becomes challenging. Chippings may occur at the cutting edges that reduce the mechanical stability of the die. Thermal load changes could then lead to sudden chip failure. A promising tool to improve the cutting quality are ultrashort pulsed lasers, because thermal side effects can be reduced to a minimum. However, ultrashort pulse laser scribing of Si leads to the formation of periodic holes – also called cone-like protrusions (CLP) - at the trench bottom. These CLPs turn into furrows with a period and depth of about 1 µm at the lower cutting edge, if a thin wafer is cut fully. The goal of this study is to investigate the influence of these defects on the backside breaking strength of the die. For this purpose, an ultrafast laser with a pulse duration of 380 fs was operated at pulse frequency of 200 kHz to cut a wafer into 2.89x3.6 mm? small chips. Wavelength (1040 nm and 520 nm), pulse energy, polarization, scan speed and number of scans was varied. The breaking strength was evaluated using the 3 point bending test. The cutting edges were investigated using confocal microscopy and scanning electron microscopy. The results indicate that the morphology of the defects at the lower cutting edge influences the backside breaking strength. Moreover, the bending test results show that ultrashort pulse laser dicing improves the breaking strength compared to mechanical dicing.

9740-43, Session 11

Influence of plasma-induced self-effects on surface ablation of glass using fs-laser pulses Javier Hernandez Rueda, Univ. of California, Davis (United States); Jasper Clarijs, Univ. of California, Davis (United States) and Utrecht Univ. (Netherlands); Jan Siegel, Javier Solis, Instituto de Óptica “Daza de Valdés” (Spain) and

+1 360 676 3290 · [email protected]

191

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI Consejo Superior de Investigaciones Científicas (Spain); Hao Zhang, Dries van Oosten, Utrecht Univ. (Netherlands); Denise M. Krol, Univ. of California, Davis (United States) Surface ablation of fused silica using single ultrashort laser pulses has been investigated. It is well-known that when an intense fs-laser pulse is focused at the surface of a dielectric its photons may locally ionize the material via non-linear absorption, giving rise to free charge carriers. In the presence of these excited electrons the local dielectric function changes dynamically, as the carrier density rises under the influence of laser photons and decays in its absence. Hence, the optical properties of the material change as the laser pulse impinges on the material surface. We have experimentally and theoretically investigated this complex physical problem from both a static and a dynamical perspective. The theoretical model, used in this work, is based on finite difference time domain (FDTD) method and allows for calculating the self-reflectivity and the temporally resolved surface reflectivity of a dielectric irradiated using fs-laser pulses. We couple the FDTD simulation to a single rate equation that describes the carrier density (driven by multiphoton ionization, avalanche ionization and recombination). Using this carrier density, the transient dielectric constant used in the FDTD simulation (Drude plus Kerr terms included) is dynamically updated. On the experimental side, we have captured images of the pump-beam that is back reflected (self-reflectivity) from the interface and studied the change in reflectivity due to laser-plasma interaction during single shot irradiation of glass. Furthermore, the e--plasma dynamics has been measured using fsmicroscopy, where the transient reflectivity was imaged for several temporal delays using a probe-beam. We discuss the effect of the temporal shape of the laser pulse on the laser energy coupling and its influence on the final surface topography.

9740-44, Session 11

Time resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials Frank Hendricks, Victor V. Matylitsky, Spectra-Physics (Austria); Matthias Domke, FH Vorarlberg (Austria); Heinz P. Huber, Munich Univ. of Applied Sciences (Germany) Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultrashort laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultrashort pulse lasers allow cutting of the chemically strengthened glasses such as Corning® Gorilla® glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics®, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for further improvement of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials on a time scale between one nanosecond to several tens of microseconds. The observed effects include pressure and rarefaction wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have helped us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

192

9740-45, Session 12

Few-cycle pulses for bulk microprocessing of fused silica (Invited Paper) Alexandre Mermillod-Blondin, Benjamin Klessen, Federico J. A. Furch, Marc J. J. Vrakking, Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (Germany) Laser pulse duration is a factor of paramount importance when considering direct laser bulk microprocessing of transparent materials in tight focusing conditions (NA ~ 0.5). Regardless of the chemical composition of the substrate, the existence of two laser-matter interaction types (Type I and Type II) is firmly established [1]. In fused silica, Type I modifications can only be obtained when using a pulse duration below 180 fs and modest pulse energies (0.1 to 0.2 ?J). The shorter the pulse duration, the wider the processing window. For instance, microprocessing with a 40-fs pulse duration results in Type I modifications for pulse energies up to 0.4 ?J.[2] Type I microstructures are characterized by a uniform, smooth refractive index higher than the refractive index of the pristine bulk. Besides, Type I microstructures are produced with no collateral damage (such as cracks or stress around the irradiated region). This combination offers a unique potential for applications such as low-stress laser marking or direct laser writing of photonic structures in thin samples. Our most recent results demonstrate that using few-cycle pulses (pulse duration < 10 fs) enables producing Type I modifications over an extended microprocessing window. The few-cycle laser source [3] is a non-collinear optical parametric amplifier (NOPA) delivering sub-7 fs laser pulses at a repetition rate of 400 kHz with a pulse energy of ~ 10 ?J. The laser pulses are focused with high numerical aperture (0.5), all-reflective optics in the bulk of pure fused silica samples. We study the influence of the irradiation conditions (pulse energy, number of pulses, numerical aperture of the focusing system) on the characteristics of the laser-induced microstructures. The characterization of the photoinduced microstructures (morphology, refractive index change) is performed with a spatial light interference microscopy apparatus. [4] References: [1]: Gross et al., “On the use of the Type I and II scheme for classifying ultrafast laser direct-write photonics” Opt. Express, 23, pp. 7767-7770, (2015). [2]: Taylor et al., “Applications of femtosecond laser induced self-organized planar nanocracks inside fused silica glass” Laser Photon. Rev., 2, pp. 26-46, (2008). [3]: Furch et al., “Improved characteristics of high repetition rate noncollinear optical parametric amplifiers for electron ion-coincidence spectroscopy” Conference on Laser and Electro-Optics, San Jose, CA, paper SF1M.5 (May 2015). [4]: Wang et al., “Spatial light interference microscopy (SLIM)” Opt. Express 19, 1016-1026, (2011).

9740-46, Session 12

Probing temporal and spatial properties of electronic excitation in dielectrics after interaction with temporally shaped femtosecond laser pulses: experiments and simulations Thomas Winkler, Univ. Kassel (Germany); Lasse HaahrLillevang, Aarhus Univ. (Denmark); Cristian Sarpe-Tudoran, Nadine Götte, Bastian Zielinski, Nikolai Jelzow, Arne Senftleben, Thomas Baumert, Univ. Kassel (Germany)

SPIE Photonics West 2016 · www.spie.org/pw

Return to Contents

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI The generation of a free electron plasma is the first step in the laser ablation of high bandgap materials. We have demonstrated that tailored ultrashort laser pulses are suitable for robust manipulation of optical breakdown, increasing the precision of ablation to one order of magnitude below the optical diffraction limit [1]. In this work, laser excitation of dielectrics under ambient conditions is investigated by temporally- and radially-resolved common-path spectral interferometry [2,3]. Besides water, fused silica and sapphire are excited by ultrashort bandwidth-limited and temporally asymmetric shaped femtosecond laser pulses, where the latter start with an intense main pulse followed by a decaying pulse sequence. Spectral interference in an imaging geometry allows measurements of the transient optical properties integrated along the propagation through the sample but radially-resolved with respect to the transverse beam profile. Since the optical properties reflect the dynamics of the free-electron plasma, such measurements reveal the spatial characteristics of the laser excitation. Furthermore, post mortem analysis of ablation structures corresponding to the spectral-interference measurements were performed. We conclude, by comparing the experiments with rate equation simulations, that temporally asymmetric shaped laser pulses are a promising tool for high-precision laser material processing, as they reduce the transverse area of excitation, but increase the excitation inside the material along the beam propagation.

9740-48, Session 12

Investigation of the micro-mechanical properties of femtosecond laser-induced phases in amorphous silica matrix Christos E. Athanasiou, Yves Bellouard, Ecole Polytechnique Fédérale de Lausanne (Switzerland) Due to its unique mechanical, optical and chemical properties fused silica is commonly used in a variety of applications, from optics to biotechnologies and more recently, as a platform of integrated microsystems combining fluidics, optics and mechanics. At the micro- and nano- scale, amorphous silica exhibits unconventional behaviour. More generally, the micromechanics of silica, as well as its polymorphic phases, remain largely unexplored due to the inherent experimental challenges associated with mechanical testing of micron-size specimens. Recently, we reported on the use of a monolithic microscale tensile tester, fabricated by a femtosecond laser, to measure fused silica’s micromechanical properties.

[3] T. Winkler et al., Appl. Surf. Sci., submitted 06/2015

The use of this instrument can be diversified for the investigation of the mechanical properties of silica’s laser-induced composite structures. Here, we will present first results on the mechanical properties of laser affected zones as well as stress relaxation phenomena of femtosecond-laser affected zones.

9740-47, Session 12

9740-49, Session PTue

Plasma dynamics and spectroscopy during fs-laser fabrication of waveguides in glass

The influence of femtosecond laser wavelength on waveguide fabrication inside glasses

[1] L. Englert et al., Opt. Expr. 15, 17855 (2007); JLA 24, 042002 (2012) [2] C. Sarpe et al., NJP 14, 075021 (2012)

Javier Hernandez Rueda, Univ. of California, Davis (United States); Dries van Oosten, Utrecht Univ. (Netherlands); Jonathan J. Witcher, Univ. of California, Davis (United States); Jasper Clarijs, Univ. of California, Davis (United States) and Utrecht Univ. (Netherlands); Denise M. Krol, Univ. of California, Davis (United States) We have studied the dynamics and the spectral dependence of the transient optical properties inside zinc aluminium phosphate glasses and fused silica under conditions of femtosecond (fs) laser waveguide fabrication. We have made use of a fs-resolved pump and probe arrangement, which allows for measuring the transient optical transmission at different wavelengths. Such experimental system has two operation modes, where either spatial (at a particular wavelength) or spectral resolution can be achieved along with temporal resolution. Transient transmission spectroscopy and microscopy together with a simple Drude-like physical model were used for inferring the maximum electron density achieved for bulk processing using tightly focused fslaser pulses. This quantitative method can be utilized for predicting the bounds where smooth or explosive processes occur inside the material. In addition, it allows us to understand the influence of processing parameters of paramount importance, such as pulse duration, polarization state or laser wavelength, on the underlying physical mechanisms. Ultimately, the acquired knowledge from the processing dynamics can be applied for improving the performance of laser-inscribed optical waveguides, i.e. reduce transmission losses or enhance refractive index contrast. In addition to temporally resolved measurements, the use of spatially resolved spectroscopy during waveguide writing was found to be a reliable indicator of the smoothness of the final optical modification. Therefore, such spectral signature, in terms of the central wavelength of the emitted spectrum, was also utilized for optimization of the inscribed waveguides.

Return to Contents

Javier Hernandez Rueda, Jasper Clarijs, Univ. of California, Davis (United States); Charmayne E. Smith, Richard K. Brow, Missouri Univ. of Science and Technology (United States); Denise M. Krol, Univ. of California, Davis (United States) We have investigated the permanent refractive index changes inside fused silica and zinc phosphate glasses after laser inscription of waveguides using ultrashort laser pulses at different wavelengths. The aim of this work is to elucidate the relationship between the laser wavelength and the materials structural changes linked to smooth optical modification. To this end the laser frequency was detuned using an optical parametric amplifier (OPA) combined with a confocal arrangement (for cleaning the laser spatial profile). Afterwards, for laser direct writing a microscope objective (10x, NA = 0.24) was used for focusing the beam inside a glass sample, which was translated along the laser propagation axis by means of a motorized translation stage. The laser-induced structural changes were measured using Raman spectroscopy both for tracks of damage and for good optical waveguides. The structural changes were inferred from peak shifts and relative intensity fluctuations associated with representative Raman bands. In the case of fused silica changes in the 605 cm-1 peak, which is due to 3-membered Si-O ring structures, were monitored while in the case of phosphate glass we focused on the 1209 cm-1 peak, which is linked to Q2-like tetrahedra. The suitability for waveguiding and the refractive index changes were respectively inspected by measuring the near and far field output profiles using a continuous wave laser at 660 nm. Since the photon energy rules the order of the multiphoton absorption in dielectrics, the role of the laser wavelength for waveguide fabrication will be discussed in terms of the influence of the ionization mechanisms on the laser energy coupling and the maximum electron density obtained.

+1 360 676 3290 · [email protected]

193

Conference 9740: Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XVI

9740-50, Session PTue

Pulsewidth dependence of laser-induced periodic surface structure formed on yttria-stabilized zirconia polycrystal Masayuki Kakehata, Hidehiko Yashiro, National Institute of Advanced Industrial Science and Technology (Japan); Ayako Oyane, Nanosystem Research Institute (Japan) and National Institute of Advanced Industrial Science and Technology (Japan); Atsuo Ito, Health Research Ctr., AIST (Japan); Kenji Torizuka, Electronics and Photonics Research Institute (Japan) and National Institute of Advanced Industrial Science and Technology (Japan) The 3-mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), which is one of fine engineering ceramics, offers advantages in application for mechanical components and medical implants due to its high resistance to fracture and flexural strength. The control of surface roughness improves the character of the device in some applications. The laser-induced periodic surface structures (LIPSS) by ultrashort pulse lasers have never been investigated for 3Y-TZP in detail. In this paper, the formation and characteristics of LIPSS formed on 3Y-TZP are reported especially focused on the pulsewidth dependence which shows unique dependence. A laboratory made Ti:sapphire chirped-pulse amplification system, which generates 810nm-centered 80-fs pulses at 570Hz repetition rate, was employed. The 3Y-TZP samples, of which surface were wet-polished to mirror quality, were made from a fine powder (TZ-3YB-E, Tosoh) with sintering temperature at 1350 ºC. The measured ablation threshold peak fluence was ~1.5 J/cm2 and the LIPSS was formed for the peak fluence of 2.7 ~7.7 J/cm2. The lines of the LIPSS was parallel to the direction of the linearly polarized light and the period of LIPSS was comparable or larger than the center wavelength of the laser. The dependence of LIPSS on pulsewidth was investigated by changing the dispersion of the pulses. The period of the LIPSS clearly increased (~860nm-1100nm) with increasing the pulsewidth (80fs - 500fs), while no dependence on the sign of the chirp was observed. These new characteristics are discussed by comparing with the LIPSS for different materials reported.

9740-51, Session PTue

Femtosecond laser waveguide writing in zinc magnesium phosphate glasses Nikolay Skovorodnikov, Javier Hernandez Rueda, Vladimir A. Semenov, Denise M. Krol, Univ. of California, Davis (United States) Femtosecond (fs) pulsed laser inscription was used to fabricate optical waveguides in ternary zinc magnesium phosphate glasses with different compositions. The main goal of this work was to find a reliable dielectric material for fs-laser waveguide writing, which has particular physical properties. The material is to be mechanically robust and chemically durable and is to exhibit positive refractive index change under fs-laser irradiation. Besides, such phosphate glass structures possess an advantageous high solubility of rare-earth ions, which can be potentially exploited for the fabrication of active photonic devices. In order to produce optical changes a fs-laser beam was focused inside the material so a sufficient intensity was reached and permanent structural modification could be induced at the focal volume. The glass samples were translated along the laser beam direction; therefore elongated optical modifications were formed. Whether the written lines were able to guide light was verified by measuring the near-field profile of the output mode of the waveguide at 660 nm. This way, optical guiding was demonstrated for the sample 25MgO 25ZnO 50P2O5 (mole %). Either tracks of damage

194

or negative refractive index changes did not allow demonstrating guiding for other compositions. The laser-induced structural changes within the glass network were studied by means of spatially resolved micro Raman and fluorescence spectroscopy. While slight or no peak shifts, of relevant Raman bands, were found, a strong fluorescence signal was measured and associated with POHC electronic defect formation. These results and corresponding changes of optical properties are discussed in relation with the O/P atomic ratios favorable for waveguide fabrication.

9740-52, Session PTue

Studying ultrafast laser parameters to deter self-focusing for deep tissue ablation Christopher Martin, Murat Yildirim, Adela Ben-Yakar, The Univ. of Texas at Austin (United States) Ultrafast pulsed lasers are a promising tool for precise and noninvasive tissue surgery. The high peak intensity of the pulses allows nonlinear interaction with tissue, causing three-dimensional confined ablation without thermal damage thanks to low pulse energies. However, deep tissue ablation has been limited to a few scattering lengths due to laser beam extinction. As pulse energies are increased to overcome attenuation, unwanted side effects can occur such as surface ablation and self-focusing, where the highly intense pulse alters the refractive index of the material, causing a lensing effect and long filaments of damage before the focus. Here, we examine the optimal laser parameters to overcome extinction and self-focusing for deep tissue ablation. Through histological images, we show that changing the pulse width from the typically used 100-200 femtosecond range to 1-2 picoseconds delays the onset of self-focusing because of the decreased power during the pulse; the pulse energy required to hit the critical power for self-focusing is increased without a corresponding increase in the pulse energy required for ablation. Additionally, we simulate the maximum ablation depth for pulses of different wavelengths, and show that wavelengths of ~1.5 microns can ablate deeply because of reduced scattering in tissue and an increase in the critical power requirement for selffocusing. We discuss other potential solutions to increase ablation depth, including temporal focusing.

9740-53, Session PTue

Analysis of human hairs and nails by femtosecond laser-induced breakdown spectroscopy Sergey S. Golik, Alexey A. Ilyin, Tamara M. Agapova, Michael Y. Babiy, Yuliya S. Biryukova, Alexander Y. Mayor, Nataliya N. Golik, Far Eastern Federal Univ. (Russian Federation) The time-resolved femtosecond laser-induced breakdown spectroscopy (LIBS) was used to analyze human hairs and nails. Spitfire Ti:sapphire amplifier system (Spectra-Physics) was used as a source of femtosecond laser pulses (