Day 2 :
Kassel University, Germany
Keynote: III-V nanowire arrays as a platform for photovoltaics, solid state lighting and electronics
Time : 09:05-09:35
Bernd Witzigmann received his PhD degree (with honors) in Technical Sciences from the ETH Zürich, Switzerland, in 2000. He then joined Bell Laboratories, Murray Hill, NJ, as a Member of Technical Staff. In 2004, he was appointed as Assistant Professor at ETH Zurich in Switzerland. Since 2008, he was Professor at University of Kassel, Germany, and Co-Director of the Centre of Interdisciplinary Nanoscience and Technology. He is author/co-author of more than 180 journal and conference publications, Chairman of a SPIE Photonics West conference, and has been Editor of several journals. He is a Senior Member of the IEEE and SPIE and Co-Director of the Nanocenter CINSaT at Kassel University.
In this presentation, the physical principles of semiconductor nanowire arrays are discussed, with a focus on applications for photovoltaics and solid state lighting. Both of these fields are pivotal for green photonics technologies. As analysis tools, specific physics-based numerical models for nanophotonics and nanoelectronics have been developed, which will be discussed. In particular, the three-dimensional nature of a wire array, including the substrate and the free space on top is included in the study. For the optical extraction efficiency of an LED, absorption of electromagnetic energy in the contacts and the active layers themselves, as well as re-emission (photon-recycling) are investigated. The latter is an effect that couples the electronic and the optical system. In addition, the optical density of states is analyzed and its impact on the extraction efficiency is shown. Finally, the total electro-optical efficiency of a nanowire array LED emitting at 400nm is presented and compared to conventional efficient thin-film LEDs. It is shown that the efficiency droop commonly observed in III-nitride based LEDs can be shifted to high operating currents. For the nanowire array solar cell, a detailed electromagnetic and electronic analysis is presented, from which fundamental rules in terms of materials choice and wire geometry will be derived. It shows that low density regular III-V nanowire arrays can reach absorptivities identical to bulk cells, with the advantage of substrate flexibility, low material consumption, and improved strain engineering for multi-junction cells. As outlook, the integration of III-V nanowire arrays for electronic and optical functional devices will be discussed and some applications are shown.
Figure 1: Optical generation rate in an InGaN/GaN core-shell nanowire solar cell
 B Witzigmann, R Veprek, S Steiger, and J Kupec, J. Comp. El., No. 4, Vol. 4, pp. 389-397, 2009, (invited).
 F Yu, D Rümmler, J. Hartmann, L. Caccamo, T. Schimpke, M. Strassburg, A. Gad, A. Bakin, H. Wehmann, B. Witzigmann, H. Wasisto, and A. Waag, Applied Physics Letters, 108, 213503 (2016)
 C. Kölper, M. Sabathil, F. Römer, M. Mandl, M. Strassburg, and B. Witzigmann, Phys. Stat. Sol. A, 1-9, 2012.
 J. Kupec, R. Stoop, and B. Witzigmann, Optics Express, Vol. 18, No. 26, p. 27589-27605, 2010.
 J. Wallentin, N. Anttu, D. Asoli, M. Huffman,I. Åberg, M. Magnusson, G. Siefer, P. Fuss-Kailuweit, F. Dimroth, B. Witzigmann, H. Q. Xu, L. Samuelson, K. Deppert, M. T. Borgström, Science 1 March 2013: Vol. 339 no. 6123 pp. 1057-1060.
Samsung Electronics, South Korea
Keynote: Nanostructured GaN light-emitting diodes on unusual substrates and blue light enhancement by surface plasmon resonance
Time : 09:35-10:05
Jun Hee Choi received his PhD in Materials Science and Engineering from Seoul National University in 2012. He is currently a Research Master and Research Staff Member of the Device and System Research Center at Samsung Advanced Institute of Technology, Samsung Electronics. He has published more than 45 papers in SCI journals, more than 20 conference papers, and more than 50 US patents. His research includes GaN-based optoelectronics on unconventional substrates, and low dimensional electronics based on quantum dots, ZnO nanorods, and graphene.
There have been significant recent developments in the growth of single crystal gallium nitride (GaN) on unconventional templates for large-area blue or green light-emitting diodes (LEDs) which, together with layer transfer onto foreign substrates, can enable flexible and stretchable lighting applications. Here, the heteroepitaxial growth of GaN on amorphous and single-crystal substrates employing various interlayers and nucleation layers is discussed, as well as the use of weak interfaces for layer-transfer onto foreign substrates. Layer-transfer techniques with various interlayers are also discussed. These heteroepitaxial GaN growth and layer-transfer technologies are expected to lead to new lighting and display devices with high efficiency and full-color tunability, which are suitable for large-area, stretchable display and lighting applications. We shall also discuss blue light enhancement in CdS/ZnS quantum dots using surface plasmon resonance to achieve near-unity quantum yield. Finally, nanostructured GaN-based LEDs for white light generation will be reviewed.
Figure 1: Atomic arrangement of various hetero-epitaxial interfaces for different multilayer structures: a) GaN/ZnO (NL)/graphite (IL/SB): (left) GaN/ZnO and (right) ZnO/graphene. b) GaN/AlN (NL)/BN (IL)/sapphire (SB): (left) GaN/AlN, (center) AlN/BN, and (right) BN/sapphire. c) GaN/Ti (IL)/glass (SB): GaN/Ti. d) GaN/AlN (IL)/Si (SB): AlN/Si. e) Interfaces connected by (left) dangling bonds (3D on 3D), (center) van der Waals gap (2D on 2D), and (right) quasi van der Waals gap (2D on dangling-bond passivated 3D).
- J H Choi (2016) Heteroepitaxial growth of GaN on unconventional templates and layer-transfer techniques for large-area, flexible/stretchable light-emitting diodes. Adv. Optical Mater. 4: 505-521.
J H Choi (2014) Fully flexible GaN light‐emitting diodes through nanovoid‐mediated transfer. Adv. Optical Mater. 2: 267-274.
J H Choi (2012) GaN light-emitting diodes on glass substrates with enhanced electroluminescence. Journal of Materials Chemistry 22: 22942-22948.
- J H Choi (2011) Nearly single-crystalline GaN light-emitting diodes on amorphous glass substrates. Nature Photonics 5: 763-769.
National Taiwan University of Science and Technology, Taiwan
Time : 10:50-11:20
Shien-Kuei Liaw received Double Doctorate from National Chiao-Tung University in Photonics Engineering and from National Taiwan University in Mechanical Engineering, respectively. He joined the Chunghua Telecommunication, Taiwan, in 1993. Since then, he has been working on Optical Communication and Fiber Based Technologies. He joined the Department of Electronic Engineering, National Taiwan University of Science and Technology (NTUST) in 2000. He has ever been Director of the Optoelectronics Research Center and the Technology Transfer Center, NTUST. He was a Visiting Researcher at Bellcore (now Telcordia), USA for six months in 1996 and a Visiting Professor at University of Oxford, UK for three months in 2011. He owned six US patents, and authored or coauthored for 250 journal articles and international conference presentations. He earned many domestic honors and international honors. He has been actively contributing for numerous conferences as a conference chair, technical program chair, organizing committee chair, steering committee and/or keynote speaker. He serves as an Associate Editor for Fiber and Integrated Optics. Currently, he is a Distinguished Professor of National Taiwan University of Science and Technology (NTUST), Vice President of the Optical Society (OSA) Taiwan Chapter and Secretary-General of Taiwan Photonic Society. His research interests are in Optical Sensing, Optical Communication and Reliability Testing
In this talk, several types of single-longitudinal mode (SLM) linear cavity tunable fiber lasers will be reviewed and discussed. Integrating a partial reflectance fiber Bragg grating (FBG) as the front cavity end, the rear cavity end elements may be a loopback optical circulator (OC), a broadband fiber mirror, a Faraday rotator mirror or a 2x2 fiber coupler. For SLM selection, using multiple subring cavities based on the Vernier effect, a piece of gain fiber saturable absorber as modes filter or their hybrid type. For wide-tuning range fiber laser, the wavelength tuning mechanism may be tunable FBGs, a 3-point bending device or a four-lamina composite device to facilitate wavelength tuning of FBGs, a large tuning range cover C+L band with good resolution of 0.1 nm was achieved. Laser characteristics such as output power, optical signal-to-noise ratio, laser linewidth, threshold pump power and pumping slope efficiency are measured. An example characteristic of 1 MHz, 59 dB, 13% and 0.1 dB for linewidth, side-mode suppression ratio, quantum efficiency and power variation of whole tuning range, respectively, are obtained. The pumping power efficiency may be 10% improved by recycling the residual pump power to the gain medium and has the advantages of simple structure, large pump slope efficiency and short cavity. The proposed fiber lasers may find various potential applications
NASA Goddard Space Flight Center, USA
Keynote: A portable laser heterodyne radiometer for measurements of CH4 and CO2 in the atmospheric column
Time : 10:55-11:25
Emily Wilson specializes in Instrument Development for measurement of atmospheric trace gases. She joined NASA in 2005 after working there as an NRC Postdoc. She leads two instrument developments: a laser heterodyne radiometer for column measurements of CO2, CH4, and H2O, and a miniaturized gas correlation radiometer for measurements of CH4, CH2O, H2O, and CO2 in the Martian atmosphere.
Laser heterodyne radiometry is a technique based on radio receiver technology that has been in use since the 1970s for measuring trace gases in the atmosphere such as ozone, water vapor, methane, ammonia, and chlorine monoxide. Earlier iterations of this technique featured large, high-powered lasers that limited widespread use and the potential for commericalization. With the relatively recent availability of distributive feedback (DFB) lasers, it has become possible to make this technique low-cost, low-power, and portable. The miniaturized laser heterodyne radiometer (mini-LHR) is a passive variation of this technology developed at NASA Goddard Space Flight Center that measures methane (CH4) and carbon dioxide (CO2) in the atmospheric column by mixing sunlight and DFB laser light in the infrared. The entire instrument fits on a backpack and operates on a fold-out 35 watt solar panel. Over the course of its development, the mini-LHR has been field tested in a range of locations and conditions including urban locations in Washington, DC and Los Angeles, a high-altitude site at Mauna Loa observatory in Hawaii, a rural location in upper Wisconsin, and a dairy farm in California. Recently, the mini-LHR was used to monitor CH4 and CO2 over varying thawing permafrost terrains. In the image, the mini-LHR (right) is shown in a collapse scar bog next to an eddy flux tower (left) at a field site near Fairbanks, Alaska. The mini-LHR operates in tandem with AERONET - a global network of more than 500 sensors that measure aerosol optical depth. The benefit of this partnership is that the mini-LHR could be readily deployed into this global network and provide validation for satellite missions as well as a long-term stand alone data product.
1.Wilson E L et al. (2017) A 4 U laser heterodyne radiometer for methane (CH4) and carbon dioxide (CO2) measurements from an occultation-viewing CubeSat, Measurement Science and Technology 28: 035902.
2.Melroy H R et al. (2015) Autonomous field measurements of CO2 in the atmospheric column with the miniaturized laser heterodyne radiometer (Mini‑LHR). Applied Physics B 120: 609-615.
3.Wilson E L et al. (2014) Miniaturized laser heterodyne radiometer for measurements of CO2 in the atmospheric column. Applied Physics B: Lasers & Optics 114, 385-393, doi:10.1007/s00340-013-5531-1.
4.Clarke G B, Wilson E L, Miller J H, Melroy H R (2014) Uncertainty analysis for the miniaturized laser heterodyne radiometer (mini-LHR). Measurement Science and Technology 25: 055204-055209.
5.Sinclair J A, Irwin P G J, Calcutt S B Calcutt, Wilson E L (2015) On the detectability of trace chemical species in the martian atmosphere using gas correlation filter radiometry.
Holon Institute of Technology, Israel
Keynote: Design of 1xN MMI power and wavelength splitters/couplers based on slot silicon waveguide structures
Time : 11:25-11:55
Dror Malka received his BSc and MSc degrees in Electrical Engineering from Holon Institute of Technology (HIT), Israel in 2008 and 2010, respectively. He has also completed a BSc degree in Applied Mathematics at HIT in 2008 and received his PhD degree in Electrical Engineering from Bar-Ilan University (BIU) in 2015, Israel. Currently, he is a Lecturer in the Faculty of Engineering at HIT. His major fields of research are Nanophotonics, Super-resolution, Silicon Photonics and Fiber Optics. He has published around 21 refereed journal papers, 20 conference proceeding papers, and 2 book chapters.
A slot-waveguide is a unique structure that enables light to be strongly confined and guided inside a narrow nanometer-scale region of low index material that is surrounded by two layers with high index material. Using this unique structure leads to a variety of advantages such as small beat length of the guided light and strong confinement in the slot region that results in extremely low losses. Choosing a slot material with lower-index value leads to a stronger confinement inside the slot region. However, a multimode interference (MMI) demultiplexer component with closer spacing between ports is very sensitive to the variation of the optical signals in the C-band (1530-1565 nm), which can influence the MMI coupler size and the performance. To overcome this problem, we choose Gallium nitride (GaN) as the slot material. GaN has a low-index value compared to Si material and is also high-index value compared to alumina or silica. Thus, the MMI demultiplexer component based silicon (Si)-GaN slot waveguide is not very sensitive to the variation of the effective refractive index that lead, the ability to separate closer wavelengths in the C-band inside the MMI coupler with good performances. We propose a novel 8-channel wavelength MMI demultiplexer in slot waveguide structures that operate at 1530 nm, 1535 nm, 1540 nm, 1545 nm, 1550 nm, 1555 nm, 1560 nm and 1565 nm. Gallium nitride (GaN) surrounded by silicon (Si) was found to be a suitable material for the slot-waveguide structures. The proposed device was designed by seven 1x2 MMI couplers, fourteen S-band and one input taper. Simulation results show that the proposed device can transmit 8-channel that works in the whole C-band (1530-1565 nm) with low crosstalk ((-19.97)-(-13.77) dB) and bandwidth (1.8-3.6 nm). Thus, the device can be very useful in optical networking systems that work on dense wavelength division multiplexing technology.
Figure 1: Normalized power as function of the operated wavelengths.
- G Je, D Malka, H Kim, S Hong, B Shin (2017) A study on micro wave of 355 nm UV-pulsed laser. Applied Surface Science.417:244-249.
- D Malka, A Peled (2017) Power splitting of 1x16 in multicore photonic crystal fibers. Applied Surface Science. 417:34-39.
- A Vegerhof, E Barnoy, M Motiei, D Malka, Y Dannan, Z Zalevsky, R Popovtzer (2016) Targeted magnetic nanoparticles for mechanical lysis of tumor cells by low-amplitude alternating magnetic field. Materials. 9(11):1-12.
- B B Ben-Zaken, T Zanzury, D Malka (2016) An 8-channel wavelength MMI demultiplexer in slot waveguide Structures. Materials. 9(11):881.
- A Vegerhof, M Motei, A Rudinzky, D Malka, R Popovtzer, Z Zalevsky (2016) Thermal therapy with magnetic nanoparticles for cell destruction. Biomedical Optics Express. 7(11):4581-4594.
Dalian University of Technology, China
Time : 11:55-12:25
Mingshan Zhao received his PhD degree in Electronic Engineering from Ghent University, Belgium, in 2003. He is a Professor in the School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian, China. He leads the Photonics Research Center at DUT, which focuses on new concepts for microwave photonic components and systems, polymer-based photonic components, and circuits for optical communication and optical sensing.
Microwave photonics (MWP) provides a unique way to synthesize, deliver and process radio frequency (RF) signal. Thanks to its numerous advantages like low transmission loss, immunity to electromagnetic interference and high bandwidth handling capacity, it is being rapidly applied into radar, satellite communication and metrology. Herein, we would like to introduce some new progresses of our research, which basically includes signal transmission, processing and detection. We proposed some methods to improve the spurious-free dynamic range of microwave photonic link (MPL), such as destructive combination of nonlinear distortions in a balanced photodiode, optical carrier band processing achieved by Stimulated Brillouin Scattering (SBS) processing and Sagnac interferometer-assisted dynamic range improvement strategy. These methods can greatly enhance the fidelity of microwave signal transmitted via an optical link, enabling realization of higher capacity with lower distortion signal transmission. We also developed some photonic techniques to eliminate in-band self-interference exists in Full-Duplex wireless communication system. We have developed a technique of optical RF self-interference cancellation by using the inherent out of phase property between the left and right sidebands of phase-modulated signal, matching their phase and amplitude to achieve self-interference cancellation. Another technique is based on a compact Dual-Parallel Mach-Zehnder Modulator (DPMZM), by detuning the electrical delay line and three bias voltage of DPMZM, the self-interference in received signal can be greatly suppressed. This work offers the possibility to achieve reliable full-duplex communications. Another work we have done is detection of low-power RF signal. It is based on a tunable optoelectronic oscillator (OEO), which can provide gain to the weak RF signals that match the oscillation frequency by tuning the wavelength of the laser. Throughout this work, it is just part of our work on MWP, further research still need to be done in the future.
- Kang Z, Gu Y, Zhu W, et al. (2016) Linearization of microwave photonic link based on nonlinearity of distributed feedback laser [J]. Optical Engineering. 55(2): 026115-026115.
- Zhu W, Hu J, Gu Y, et al. (2016) Dynamic range improvement of a microwave photonic link based on brillouin processing [J]. IEEE Photonics Technology Letters. 28(23): 2681-2684.
- Zhu W, Zhao M, Fan F, et al. (2017) Sagnac interferometer-assisted microwave photonic link with improved dynamic range [J]. IEEE Photonics Journal. 9(2): 1-9.
- Fan F, Hu J, Zhu W, et al. (2017) Dual-loop optoelectronic oscillator based on a compact balanced detection scheme [J]. Optical Engineering 56(2): 026107-026107.
- Gu Y, Zhao J, Hu J, et al. (2016) All optical up-converted signal generation with high dispersion tolerance using frequency quadrupling technique for radio over fiber system [J]. Optics & Laser Technology 79: 153-157.
National Cheng Kung University, Taiwan
Time : 12:25-12:55
Shu-Chun Chu received her PhD degree from the Institute of Electro-Optical Engineering, National Chiao Tung Univisity. She currently serves as a Professor in Department of Physics, National Cheng Kung University. She has her expertise in designing laser cavity and finding approaches for generating various structure beams in solid-state lasers. She also has expertise in designing non-imaging optical systems, such as solar concentrators, LED illuminators, backlight modules, etc.
Helmholtz–Gauss beams (HGBs), nearly non-diffraction beams that can propagate a long distance without significant divergence, have attracted considerable attention for their potential applications in science and technology. Mathieu-Gauss beams (MGBs) are one kind of Helmholtz–Gauss beams, which are the ideal non-diffraction Mathieu beams apodized by Gaussian transmittance. Unlike the ideal non-diffracting Mathieu beams, MGBs can be realized experimentally for the reason that MGBs carry a reasonable finite power. The nearly non-diffraction properties of MGM show their potential to lots of practical applications, such as: optical interconnections, laser machining, collimation and measurement, optical manipulation, etc. Alvarez-Elizondo et al. first generated MGBs in an axicon-based stable resonator in a real CO2 laser by slightly breaking the symmetry of the cavity in 2008. Later, Tokunaga et al., adopted special micro-grain Nd:YAG laser crystals, they also achieved spontaneous MGMs oscillation in end-pumped solid-state lasers. A general approach for the selectively excitation of any specified MGM in a laser system is necessary for the development of future MGBs’ applications. This study investigated in finding a way to selectively excite any specified MGM in an end-pumped solid-state laser system with an intra-cavity spatial light modulator. We drafted codes to simulate the lasing operation of the laser system to explore the selectively exciting a specified MGM in end-pumped solid-state lasers using numerical simulation. This study proposed a systematic approach to the selective excitations of all Mathieu-Gauss modes (MGMs) in end-pumped solid-state lasers with a SLM-based stable laser resonator.
Figure 1: It shows propagation of amplitude profile along plane (x, z) or plane (y, z) of an even MGB from the simulated laser resonator with mode order m=2 and ellipticity parameter q=5.
1.K F Tsai and S C Chu (2016) Characteristic matrix operation for finding global solution of one-time ray-tracing optimization method. Opt. Express 24(19): 21340-21352.
2. S C Chu, H L Yang, Y H Liao, H Y Wu, and C Wang (2014) One-time ray-tracing optimization method and its application to the design of an illuminator for a tube photo-bioreactor. Opt. Express 22(5): 5357-5374.
3.C F Kuo and S C Chu (2013) Numerical study of the properties of optical vortex array laser tweezers. Opt. Express 21(22): 26418-26431.
4.H Y Wu and S C Chu (2013) Ray-leakage-free sawtooth-shaped planar lightguide solar concentrators. Opt. Express 21(17): 20073-20089.
5.K Otsuka and S C Chu (2013) Microchip solid-state cylindrical vector lasers with orthogonally polarized dual laser-diode end pumping. Opt. Lett. 38: 1434-1436.
- Lasers Types | Laser Application | Solid-State Lasers
Lap Van Dao
Swinburne University of Technology, Australia
University of Ottawa, Canada
P N Lebedev Physical Institute, Russia
Andrei Kotkov has his expertise in Laser Physics. He received his MS degree from the Moscow Physical-Technical Institute (State University) in 1982 and his PhD degree from the P N Lebedev Physical Institute (LPI) in 2001. He is Associate Professor focusing on Laser Physics at the LPI.
In mid-IR range molecular gas lasers can simultaneously emit dozens or hundreds of spectral lines. The spectral lines of gas lasers are quite narrow, but they are located relatively rare. A carbon dioxide CO2 laser can emit dozens spectral lines in the wavelength range from 9 to 11 microns. A carbon monoxide (CO) laser operating on fundamental and first-overtone vibrational transitions has an extremely broad emission spectrum consisting of more than a thousand spectral lines in the wavelength range from 2.5 to 8.2 microns. However, all laser lines do not cover entirely specified spectral ranges. To enrich and expand the laser spectra, it is worth to apply the frequency conversion in nonlinear crystals. To enrich CO laser spectrum, frequency conversion in ZnGeP2 (ZGP) crystal was applied. Hundreds of new spectral lines were obtained due to sum-frequency generation (SFG) as the first stage and difference-frequency generation (DFG) as the second stage of two-stage frequency conversion. The ZGP crystal is a very efficient nonlinear crystal but it is transparent only up to 12 mm. Then for mixing CO and CO2 laser light we used AgGaSe2 (AGSe), GaSe, and PbIn6Te10 (PIT) crystals. Application of AGSe crystal as a frequency converter of CO and CO2 laser radiation resulted in 16.6 mm DFG. The conversion efficiency of DFG under mixing CO and CO2 laser light in AGSe appeared to be 20 times that of GaSe, which probably is related to high birefringence of the latter resulting in high spatial walk-off effect. We believe that the developed laser system can be a prototype for the development of IR laser systems and would be useful in a variety of researches and applications.
Xiaoyi Bao is the Canada Research Chair Professor (Tier I) in Fiber Optics and Photonics in Center for Research in Photonics, Physics Department, University of Ottawa, Canada. Her research interests range from study of nonlinear effects in fibers to make fiber device, lasers and sensors. She has co-authored over 260 refereed journals and 210 conference proceeding papers, 9 book chapters, and 6 IPs/patents from her group have been transferred to industries. She is a Fellow of Royal Society of Canada (RSC), OSA and SPIE.
Random fiber lasers (RFLs) with unique frequency and phase properties have attracted much attention. Comparing with the fixed cavity length lasers, RFLs rely on a scattering medium, where multiple scattering lights due to spatial inhomogeneity is captured by the fiber waveguide and amplified through different gain media leading to one-dimensional lasers with good directionality. The frequency, phase and intensity noises of RFLs have strong dependency on the free mean length (Δl) of the scattering medium. Through our experiments, we observed three different cases relative to the fiber length L, wavelength λ: (1) when Δl>λ, the frequency jitter is the highest, although relative intensity noises (RIN) and the linewidth (<5 kHz) is comparable to the phase locked laser. The random feedback can be realized by writing random grating at sub-mm spacing; (2) when Δl~λ; the linewidth can be <100 Hz with long fiber (L≥5 km), RIN is increased due to large number of the random modes, while the frequency noise is reduced; (3) Δl<λ, the RIN and frequency noise are the lowest, and the linewidth is ~10 Hz, which can be used as reference for laser linewidth characterization. The gains of the RFLs are: Er-doped fiber (EDF), Brillouin and Raman amplification and SOA. The high RIN in RFLs can be used for the random number generators (RNGs) at high speed (MHz to GHz). The distributed feedback allows multiple wavelengths operation in the laser without phase matching condition of 2 πm (m is integer) constraint in the wavelength selection, and hence it can be used as tunable microwave generator. For the Brillouin scattering, the random mode injection acts as the mode selection element, which allows single mode operation and high order Brillouin frequencies with the high contrast and narrow linewidth (1 kHz). The random gratings can be used as random feedback and sensing head to achieve high sensitivity thanks to the lasing gain for large dynamic range. The temperature, strain and refractive index and ultrasound sensing has been demonstrated.
Etsuji Ohmura is a Professor of the Osaka University, Japan. His main field of research is intelligent laser processing systems, especially theoretical analysis and computer simulation to gain deeper understanding of the complicated physical phenomena in laser material processing, influence of laser optics, and nonlinear optical phenomena.
The purpose of this study is elucidation of the process mechanism in the microprocessing of glass by an ultrashort pulse laser. In order to achieve this purpose, the plasma behavior due to femtosecond laser irradiation was observed by a high-speed camera, and laser absorption by plasma was investigated. In the experiments, pulse duration was 290 fs@1028 nm, repetition frequency was 20 kHz, traveling speed was 3 mm/s, and pulse energy was 3.8 µJ, 4.5 µJ and 5.4 µJ. The experimental results showed that there are three patterns of the plasma behavior depending on the pulse energy. Plasma is generated and disappears periodically when the pulse energy is 3.8 µJ. For pulse energy 4.5 µJ, plasma exists always and the lower part of plasma vibrates little by little. When the pulse energy is 5.4 µJ, the plasma is divided, rises to a constant depth, and then the top lump of plasma disappears. These processes are repeated periodically during several tens of pulses. The threshold fluence of laser absorption by plasma was estimated comparing rising of plasma with change of the laser fluence on the optical axis. Then the relationship between rising velocity of plasma and fluence on the optical axis was investigated. Absorption energy increases as the fluence on the optical axis becomes large and the rising velocity of plasma increases. From these series of observation of plasma behavior and investigation of plasma absorption, a simple laser absorption model by the plasma was proposed. This absorption model was applied to the plasma behavior observed, and the energy absorbed in each of divided plasma was estimated. The estimated absorptance was compared with the absorptance measured in the internal processing experiment. For different pulse energy, the estimated absorptances agreed comparatively well with the experimental values, and the validity of the proposed absorption model was confirmed.
Figure 1: Schematic chart of one period of plasma behavior obtained by high-speed video analysis (upper), and estimated energy which is absorbed by each plasma (lower). E(z) is laser energy at the depth z and Ea(x) is energy absorbed by each plasma at the traveling distance x.
Lap Van Dao is a Professor and Leader of Ultrafast Laser Science Group at Centre for Quantum and Optical Science, Swinburne University of Technology. His research activities are the development and application of ultrafast and high power laser for imaging and ultrafast time-resolved laser spectroscopy in semiconductor quantum structures and biological systems
The high-order harmonic generation process provides methods to produce short pulses of coherent radiation in the extreme ultraviolet and soft X-ray region. Soft x-ray light sources will provide new nonlinear spectroscopic tools that can be used to reveal core-level electronic resonances and their interactions, and permit the creation of no stationary electronic wave-packets and monitoring their dynamics. We investigate the creations of coherent extreme ultraviolet sources with phase-matched generation, wave-mixing and amplification process where two multiple-cycle pulses with incommensurate frequencies (at 1400 nm and 800 nm) are used. A 800 nm, 10 mJ, 30 fs, 1 kHz repetition rate laser beam is split into two beams, with pulse energies of 6 mJ and 4 mJ. The 6 mJ beam is used to pump a three-stage optical parametric amplifier (OPA) system to generate an infrared (IR) pulse at 1400 nm with energy ~2 mJ and duration 40 fs. The 4 mJ beam (800 nm) is used to mix with the 1400 nm field. The high intensity pulse (1400 nm or 800 nm) is used for phase-matched generation of XUV pulses and the other pulse (800 nm or 1400 nm respectively), which is used to control the HHG output and for generation of mixing fields or amplification, is aligned collinear or at a very small angle (<100) to the direction of the high intensity beam by a dichroic mirror. The time delay between the two pulses is controlled by a motorized delay stage with 0.1 fs resolution. The spectrum and intensity of the XUV radiation generated by the first pulse varies markedly with the influence of the second pulse. The coherence of free electron wave-packet can be obtained by time evolution of mixing fields.
Shanghai Institute of Optics and Fine Mechanics - CAS, China
Jianlang Li is a Professor at Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences, and his research is in the field of Laser Sciences. He has the interest in the development of high-power vector and vortex laser. As a pioneer, he developed the first radially polarized fiber laser, and thereafter extended it to the high-power and pulsed operation. Until now, he has been playing a leading role in the field of Vector Fiber Laser. He also revealed the efficient and high-power excitation of both radial and azimuthal polarizations in solid-state laser by combining the end-pumped microchip laser geometry with the photonic crystal grating mirror. In recent years, he developed highly efficient vector and vortex solid-state laser. Most recently, He invented the maglev and optically-driven rotary disk laser.
Statement of the Problem: The Laguerre- Gaussian (LG) beam is known as doughnut-shaped cross section and spiral phase wavefront. The exponential term exp(−imφ) in its amplitude expression grants an orbit angular momentum to the beam photon, and such the vortex beam on LG modes becomes valuable for numerous applications such as optical manipulation, super-resolution microscopy, quantum communication, gravitational-wave detection, etc. Presently Ti-doped sapphire laser is one of the most common types of solid-state laser, which can generate femtosecond pulses with high peak power up to terawatt or petawatt level and be used in the fields of plasma physics, ion acceleration, etc. A new and interesting line for this laser is to generate vortex laser emission, which would be undoubtedly much more valuable for various kinds of applications in fields like the strong-field laser physics, etc. Nevertheless, the concern on vortex Ti: sapphire laser is much inferior to those in Nd: YAG and Yb: YAG lasers.
Methodology & Theoretical Orientation: We fabricated several spot defect spatial filters (SDSFs) with different sizes (i.e. diameters), then inserted them into an ever-built Ti: sapphire laser. The SDSF was antireflection coated glass plate containing a laser-treated opaque region of a circular shape. By inserting the SDSF into the laser cavity, the effect of the sizes of SDSF on the transverse laser mode and laser power was analyzed.
Findings: The Ti: sapphire laser emitted vortex LG01 mode at proper size of SDSF and pump power. When applying a spot defect with 140-mm diameter, the power of vortex LG01 mode reached 135 mW and the slope efficiency of the laser was 17.7%.
Conclusion & Significance: In summary, this study reported the first vortex LG01-mode Ti: sapphire laser. By using SDSF as intracavity mode selector, we demonstrated a vortex Ti: sapphire laser that emitted 800-nm and LG01-mode vortex light. The next investigation will focus on the mode-locked operation of the vortex Ti: sapphire laser by applying intracavity spot defect for spatial filtering.
Jianqiang Zhu is working as a Senior Professor of Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS). He has been devoted to the long-term study in the fields of high-power laser system. This includes laser device design, optical engineering, optical beam propagation and control etc. As a Chief Scientist, he was responsible for several major projects such as Shenguang-II (SG-II) laser facility, SG-II multifunction high-energy laser systems, upgrading SG-II laser device, 3ps petawatt and 30fs multi-petawatt laser facilities, which has contributed immensely to the establishment and development of high-power laser system for ICF study in China. “SG-II multifunction high-energy laser systems” has won the National Science and Technology Progress Award in 2013. He has published 320 papers on international journals and holds 50 patents where including 4 patents in USA and Japan. And more than 50 Doctoral theses were completed under his supervision.
National Laboratory on High Power Laser and Physics (CAS) has long been committed to the researches on high-power laser system and high-energy density physics. The SG-II facility in the lab is of great importance in advancing national strategic high-tech innovation, basic science and innovation at the frontiers of interdisciplinary science. High power laser device is an ultra-precision optical system running under the condition of high flux, which contains thousands of large-aperture optical components. Optical component performance will directly or indirectly affect the overall performance of the laser system. To ensure stable operation of the system, a set of optical component technical specifications are established, including laser characteristics, wavefront characteristics, loss characteristics and characteristics of the damage. In this presentation, we analyses the character for high power laser optics components, and give the technique to manufacture. We provide a reference for improving the surface defect standard and optimizing the design of high-power laser system.
- Exhibitor Session
CHINESE LASER PRESS, China