Proceedings Volume 6100

Solid State Lasers XV: Technology and Devices

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Proceedings Volume 6100

Solid State Lasers XV: Technology and Devices

View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 22 February 2006
Contents: 11 Sessions, 62 Papers, 0 Presentations
Conference: Lasers and Applications in Science and Engineering 2006
Volume Number: 6100

Table of Contents

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Table of Contents

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  • Compact Lasers and Harmonics
  • Microchip Lasers and Systems
  • Eye-Safe and Mid-infrared Lasers (joint session)
  • Mode Locked and ULF Lasers
  • Tunable Lasers
  • Laser Materials and Components
  • High Power Lasers
  • Harmonic Power Scaling
  • Frequency Converted Lasers (Joint Session)
  • Laser Systems Designs, Modeling, and Applications
  • Special Session: Space Qualified Laser Components and Systems I
Compact Lasers and Harmonics
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Size-scaling of TEM00 mode optically pumped semiconductor lasers
Lukas E. Hunziker, Chris Ihli, Daniel S. Steingrube, et al.
The use of a dynamically stable telescopic cavity to compress the cavity length of intra-cavity doubled, TEM00 mode, optically-pumped semiconductor lasers (OPSL's) is evaluated. We find that the cavity length may be adjusted (approximately) between the Rayleigh lengths of the mode sizes on the end mirrors without sacrificing output power or dynamic stability. Consequently, for a 10 W OPSL, the length may be scaled between about 1 and 100 cm. In addition, we calculate that in all respects, the cavity stability range and misalignment sensitivity maintain practical values to about 1 cm cavity length. These results are applied to demonstrate OPSL's producing TEM00 mode outputs of 11.5 and 7.3 W at 531 and 486 nm with resonator footprints as small as 15 mm.
Optically pumped semiconductor lasers at 505 nm in the power range above 100 mW
Wolf Seelert, Stefan Kubasiak, Johannes Negendank, et al.
Lasers based on optically pumped semiconductors (OPS) offer unique capabilities in both wavelength tailoring and power scaling compared to traditional solid-state lasers. In particular, these lasers can be designed in wavelength to realize for instance 505nm, which enables excitation of two fluorescent dye chemistry sets originally established by 488 and 514 nm legacy argon lasers. Highly efficient intra cavity frequency doubling of an 1010nm OPS yields over 100 mW of output power at 505 nm. In this paper we will present a brief background on OPS technology. We will then discuss specifics of the 505 nm laser and present both performance and reliability data for this laser.
Continuous-wave visible laser by intracavity-doubled fiber laser
Tatsuya Shinozaki, Yushi Kaneda, Yoshiharu Urata, et al.
A novel continuous-wave blue-green laser was developed by the second-harmonic generation of the emission from Yb doped gain fiber. The laser cavity consists of a fiber Bragg grating (FBG), a gain fiber, an aspheric lens, a dichroic mirror for output coupling of second harmonic, a periodically-poled LiNbO3 (PPLN), and a high reflector. The intracavity-doubled fiber laser was pumped by a 580-mW, fiber pigtailed laser diode at 974 nm through the FBG. The Yb laser emission from the fiber end was focused onto the high reflector, providing optical feedback and forming the resonator. The PPLN was placed near the flat end mirror, where the waist is formed, in order to increase the fundamental intensity. The emission wavelength can be selected by changing the FBG within the bandwidth of the gain fiber. An FBGs for 1017.6 nm was selected for the experiment. Circulating power of the fundamental wave in the cavity was measured to be approximately 1500 mW when a 5% output coupler was placed instead of high-reflecting mirror. Stable output in excess of 30 mW at 508.8 nm was obtained. The optical-optical efficiency from the pump power to the visible output was about 5%. The fluctuation of the laser output power was less than 0.5% for more than 2 hours without a power feedback loop. The M2 value was measured to be 1.2. Wavelength-selectable lasers will be useful for applications including fluorescent microscopy, biological imaging, flow cytometry and spectroscopic analysis.
Microchip Lasers and Systems
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Ceramic Yb:YAG microchip laser
Eric P. Ostby, Richard A. Ackerman, Jean C. Huie, et al.
An efficient microchip laser utilizing domestically fabricated ceramic Yb:YAG is presented. In continuous-wave (cw) and Q-switched operation, the laser maintains linear polarization with 22 dB extinction and oscillates in the fundamental TEM00 mode. In cw mode, the ceramic laser has an output power of 2.25 W and a slope efficiency of 66%. When passively Q-switched at 11.4 kHz repetition rate using Cr:YAG, the 1.9 ns pulse has an average power of 0.72 W and a slope efficiency of 46%. To our knowledge, this is currently the highest reported power from a ceramic Yb:YAG laser. The laser performance of the 5-at.% ceramic is compared to a 10-at.% single crystal, and we discuss how the scattering loss and storage efficiency of the ceramic medium affect its laser characteristics.
Microchip laser operating at 1338 nm
Q-switched microchip laser emitting radiation at wavelength 1338 nm was designed and realized. This laser was based on monolith crystal which combines in one piece a cooling undoped part (undoped YAG crystal, 4 mm long), active laser part (YAG crystal doped with Nd3+ ions, 12 mm long) and saturable absorber (YAG crystal doped with V3+ ions, 0.7 mm long). The diameter of the diffusion bounded monolith was 5 mm. The initial transmission of the V:YAG part was 85 %. The microchip resonator consists of dielectric mirrors directly deposited on the monolith surfaces. The pump mirror (HT for pump radiation, HR for generated radiation) was placed on the undoped YAG part. The output coupler with reflection 90 % for the generated wavelength was placed on the V3+-doped part. Q-switched microchip laser was tested under pulsed, and CW diode pumping. The pulse length it was the same for all regimes equal to 6.2 ns. The wavelength of linearly polarized laser emission was fixed to 1338 nm. The pulse energy depends on the mean pump power. For pulsed pumping the output pulse energy was stable up to mean pump power 1 W and it was equal to 135 μJ, which corresponds to peak power 22 kW. In CW regime for pumping up to 14 W the pulse energy was stabilized to 37 μJ (peak power 6 kW). The mean output power increased up to 0.4 W only by increase of the generated pulse repetition rate (11 kHz for mean pump power 14 W).
Subnanosecond tunable dye laser pumped by a Nd:YAG microchip laser
Adam M. Jones, Orven F. Swenson
We have demonstrated a narrowband Littman configuration dye laser longitudinally pumped by the second harmonic of a 250 Hz pulse repetition frequency microchip laser with up to 50 microjoule pulse energies at 532 nm. Rhodamine 6Gd ye in methanol with a 5 cm cavity length produced 9 microjoule pulses with a slope efficiency of 20% at the peak intensity. The dye laser can be tuned from 550 to 575 nm. A 532 nm pump threshold below 4 microjoules was observed. Adding tunability to compact, economical microchip lasers with a spectrally narrow pulsed dye laser provides ideal characteristics for biotechnological applications.
Highly efficient ultra-low threshold miniature cerium fluoride lasers generating sub-nanosecond pulses at 287nm and 311nm
Hua Liu, David J. Spence, David W. Coutts
Ultraviolet (UV) miniature cerium fluoride lasers have been demonstrated using a low cost, frequency-quadrupled microchip Nd:YVO4 pump laser. The concept of miniature configuration of the cavities was shown to improve the laser performance in the low pump power region. Using a 10 μJ, 266nm pump pulse, we have obtained output energies of 3.5μJ at 287nm and 0.65 μJ at 311nm. The slope efficiencies were 45% and 35%, and the pump thresholds 2 μJ and 0.8 μJ respectively. Tunable operation of these lasers provides a simple compact wavelength converter from 266 nm to 282-333 nm.
Low-cost 7 mW CW 355-nm diode-pumped intracavity frequency-tripled microchip laser
Nicolas Aubert, Thierry Georges, Corinne Chauzat, et al.
Low noise CW milliWatt scale UV lasers are needed for many analysis applications in the semiconductor and the biological fields. Intracavity tripling has been widely used to improve the UV output power of Q-switched or modelocked lasers, but no efficient diode-pumped CW UV laser was ever reported. One of the key to success is the use of a monolithic laser structure which both eliminates the birefringence interference issue and facilitates the single frequency operation. The monolithic structure is obtained by optically contacting crystals. It does not require any alignment, reduces the manufacturing cost and improves reliability. The optimization of the amplifying medium and doubling and tripling crystals involves as many parameters as pump absorption, thermal lens, cavity length, 1064 nm mode size, walk-off, acceptance angles, polarizations, phases... The interplay between these parameters will be discussed. Finally, several amplifying media (Nd:YAG and Nd:YVO4), doubling crystals (KTP, KNbO3, BBO, BiBO and LBO) and tripling crystals (BBO, BiBO, LBO) were tested. With a 2.4W 808 nm diode pump, several configurations have led to low noise 355 nm single frequency operation exceeding 5 mW. We believe that this power can still be improved.
Eye-Safe and Mid-infrared Lasers (joint session)
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High-power fiber-bulk hybrid lasers
We report on recent progress in power scaling of cladding-pumped Er,Yb and Tm-doped silica fiber lasers in the ~1.5μm and ~2μm spectral regimes respectively, and also on some recent developments in fiber-bulk hybrid lasers based Er:YAG and Ho:YAG operating at ~1.6μm and ~2.1μm respectively. A cladding-pumped Tm-doped silica fiber laser pumped by a beam-shaped diode-stack at 790nm and with core composition optimized for efficient 'two-for-one' cross-relaxation yielded 66W of continuous-wave output at ~2μm for 117W of launched pump power. The corresponding slope efficiency with respect to launched pump power was 61%. An Er,Yb fibre laser, cladding-pumped by two spatially-multiplexed diode-stacks at 976nm and with core composition optimized for efficient energy-transfer from Yb3+ to Er3+, yielded up to 188W of continuous-wave output at 1570nm with an average slope efficiency with respect to launched pump power of 41%. The prospects for a further increase in output power from Tm and Er,Yb fiber lasers are considered. Efficient operation of hybrid Er:YAG and Ho:YAG lasers, pumped in-band by Er,Yb and Tm doped fibre lasers operating at 1532nm and 1907nm respectively has been demonstrated. Both lasers, when operated in continuous-wave mode, had slope efficiencies with respect to incident pump power of ~80%. The Er:YAG laser produced ~60W of continuous-wave output at 1645.3nm for 82 W of incident pump power, and, in Q-switched mode, produced pulses of energy, ~5.5mJ and duration, ~81ns (FWHM) corresponding to a peak power of ~67kW at a repetition rate of 500Hz for an incident pump power limited by the onset damage to 16.8W. The prospects for further improvement in continuous-wave and Q-switched performance are discussed.
100-megawatt power Q-switched Er-glass laser
John Taboada, John M. Taboada, David J. Stolarski, et al.
A very high energy Q-switched Er-glass laser is reported. We incorporated a rotating, resonant mirror/Porro-cavity reflector optical arrangement to achieve very high shutter speeds on the cavity Q of a laser designed for energetic, flashlamp-pumped, 600-μs, 1540-nm pulses. Reproducible 3.75-J, 35-ns, 1533-nm laser pulses were obtained at a repetition rate less than 1 minute. Our work shows that reliable, very high energy, Q-switched, Er-glass laser pulses at 1533 nm can be generated mechanically with no apparent damage to laser cavity components. We demonstrate the applications of this "eye safe" wavelength to energetic processes such as LIBS and materials processing. The laser could also serve as a new tool for bioeffects studies and targeting applications.
Power scaling of 1617-nm Er:YAG laser operation using a narrow bandwidth output coupler
We demonstrate Er:YAG laser operation at 1617nm with 6W output power and good beam quality (M-squared = 1.5) using a Volume Bragg Grating (VBG) as a wavelength selective output coupler. The low quantum defect operation of 5% is achieved by resonant pumping with a 1534nm fiber pump laser. The thermal loads of the crystal under 1617nm laser operation, under 1645nm laser operation, and under a no lasing condition are determined.
Saturable absorbed Er:YAG Q-switched laser with short pulse
We demonstrate passively Q switched 2% doped Er:YAG laser operation in the eyesafe region with sub 5 nsec pulse widths using Cr2+:ZnSe as a saturable absorber. A rod geometry operating in the burst mode and a micro slab geometry operating continuously are described. The micro slab geometry generates 6nsec passively Q switched pulses with over 1.5 Watt of output power and with multi kilohertz pulse repetition rates. The lasers are resonantly pumped with a 1534nm fiber laser.
3.9-4.8μm gain-switched lasing of Fe:ZnSe at room temperature
J. Kernal, V. V. Fedorov, A. Gallian, et al.
Absorption and luminescence properties of Fe:ZnSe and Fe:Cr:ZnSe crystals in the middle infrared spectral range were studied at room and low temperatures. Room temperature emission cross section of 5T2->5E transmission of iron ions was estimated from spectroscopic measurements. Middle infrared emission of Fe2+ in ZnSe was studied under three different regimes of excitation: direct optical (2.92 μm) excitation of 5T2 first excited state of Fe2+, excitation via 5E level of Cr co-dopant (1.56 μm), and excitation via photo-ionization transition of Fe2+ (0.532 μm). For the first time the energy transfer from Cr2+ (5E level) to Fe2+ (5T2 level) under 1.56 μm wavelength excitation was observed and resulted in simultaneous room temperature emission of Fe:Cr:ZnSe crystal over ultra-broadband spectral range of 2-3 and 3.5-5 μm. We also report the first observation of middle infrared emission at 4.5 μm induced by 2+->3+->2+ ionization transitions of iron ions in Fe2+:ZnSe. The first room temperature gain-switched lasing of Fe:ZnSe crystal at 4.4 μm wavelength was demonstrated. Room temperature tunable oscillation of Fe:ZnSe crystal over 3.9-4.8 μm spectral range was realized.
Mid-infrared (3-5 μm) emission from rare earth doped KPb2Br5
Solid-state lasers operating in the mid-infrared (MIR) wavelength region (3-5 μm) are of significant current interest for laser remote sensing of chemical and biological agents as well as for military countermeasures. The development of MIR solid-state lasers based on oxide and fluoride laser hosts is limited by non-radiative decay through multi-phonon relaxations. Rare earth doped crystals with low maximum phonon energies can exhibit efficient MIR emission at room temperature. In this paper, we present results of the material synthesis and optical properties of rare earth (Pr, Nd, Dy, Er) doped KPb2Br5, which has a maximum phonon energy of only ~140 cm-1.
Mode Locked and ULF Lasers
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Future trends and applications of ultrafast laser technology
Jason M. Eichenholz, Mingwei Li, Ian Read, et al.
In this talk we will present an overview of recent development of ultrafast lasers sources and their applications. This talk will highlight some recent state of the art ultrafast pulse results from Ti:Sapphire and Ytterbium based laser systems. There are significant advantages in being able to directly diode pump Ytterbium materials resulting in more compact bulk solid state and fiber based laser systems. Several newly emerging technologies such as Optical Parametric Chirped Pulse Amplification, and Supercontinuum Generation have generated great excitement in recent years. The evolution of more compact and user friendly ultrafast laser systems has enabled completely new fields that take advantage of the extremely high peak powers and very short time duration of ultrafast laser pulses. Recent results in the fields of multiphoton microscopy, micromachining, 3-D fabrication, and spectroscopy will be discussed.
High energy 40 fs compact diode-pumped femtosecond laser for nanostructuring applications
High peak power femtosecond oscillators exhibit great potential for many applications such as micro- and nanomachining and structuring, waveguide writing in glass, nonlinear frequency conversion or seeding of ultrafast fiber and bulk amplifiers. Ultrashort pulse durations below 50 fs are routinely produced by Ti:sapphire lasers. However, due to the need for a green pump laser, Ti:Sapphire lasers suffer from a greater complexity. Diode-pumped Ytterbium femtosecond lasers on the other hand are compact and reliable lasers, but, because of the limited amplification bandwidth, typically exhibit pulse duration greater than 60 fs. We present a directly diode-pumped 40-fs laser source with pulse energies higher than 120 nJ, more than 2 MW peak power, and a pulse repetition rate of 9 MHz. The laser setup is compact and fits in a 60 x 40 cm footprint. The laser source consists of a passively mode-locked femtosecond oscillator and fiber-based post-compression module. The oscillator operates at 9 MHz pulse repetition rate and produces pulse energies up to 300 nJ at 370 fs pulse duration. The oscillator is then focused into a standard single mode fiber in order to broaden the pulse spectrum to about 60 nm bandwidth. Owing to the high initial pulse energy the used fiber is as short as 15 mm. After collimation it was sufficient to reflect the beam 8 times on 2 parallel chirped mirrors having 250 fs2 each. The overall transmission of this pulse compression module was about 80% resulting in 120 nJ transmitted pulse energy in 40-fs pulses.
Generation of 47-fs pulses from a diode-pumped Yb3+:CaGdAlO4 femtosecond laser
Yoann Zaouter, Justine Boudeile, Frederic Druon, et al.
The demonstration of a directly diode-pumped mode-locked femtosecond oscillator based on an ytterbium-doped CaGdAlO4 single crystal is reported. The 2-at.% Yb3+-doped, 2.5-mm-thick sample is directly diode-pumped by a high-brightness 5W fiber-coupled laser diode and the mode-locked regime is achieved by use of a SEmiconductor Saturable Absorber Mirror (SESAM). This configuration allows the generation of pulses as short as 47 fs at the central wavelength of 1050 nm, which are to our knowledge the shortest laser pulses ever obtained from a bulk ytterbium-doped laser. The average power is 38 mW and the repetition rate is 109 MHz. In a preliminary test, we built a three mirror folded cavity in which we inserted a single SF10 prism and obtained a very large and smooth cw tunability that spanned from 1013 nm to 1059 nm.
Generation of 13.5-fs pulses from a diode-pumped Kerr-lens mode-locked prismless Cr:LiSGaF laser
The self-amplitude modulation of Kerr-lens mode-locked colquiriite lasers was maximized by pumping scheme, resonator geometry and group-delay dispersion. The realized compact, maintenance-free and battery-powered Cr:LiSGaF laser achieves 13.5fs pulse-width and 102mW output power.
Cryogenically cooled Ti:sapphire amplifiers
Alan Fry, Steve Fournier, Jean-Marc Heritier, et al.
Power scaling in laser systems is fundamentally constrained by detrimental effects of absorbed heat in the lasing medium. Cryogenic cooling is a well known technique for improving thermal performance in solid state laser materials. In particular the dramatic improvement in the thermal properties of Ti:sapphire at cryogenic temperatures has enabled a new class of commercial high-average-power femtosecond Ti:sapphire amplifiers. We review recent developments in this technology.
Cryogenic Faraday isolator for high average power lasers
D. S. Zheleznov, A. V. Voitovich, I. B. Mukhin, et al.
It is experimentally demonstrated that cooling Faraday isolators to liquid nitrogen temperature considerably decreases thermally induced depolarization and thermal lens. This allows a 30 times increase in maximum average power of laser radiation going through the isolator at the same isolation ratio. It is shown that traditional Faraday isolators under such cooling conditions can operate at powers up to 10 kW, and Faraday isolators with compensation of depolarization and thermal lens - at powers up to 100 kW.
Acousto-optically Q-switched and mode-locked diode-pumped Nd:YVO4 laser
The compact picosecond, high power lasers are demanded in several areas e.g. micromachining, ophthalmology etc. One of the promising methods enabling generation of picosecond pulses trains with energies of a few μJ each in a simple resonator is the simultaneous Q-Switching and Mode Locking (QML) regime. We have demonstrated the efficient QML regime applying acousto-optic modulator in double role as an active Q-switch and mode locker. The pumping beam, emitted by 20-W laser diode bar with beam shaper forms the caustics of 0.8-mm width inside the 0.3 at.% Nd3+ doped 10-mm-long YVO4 crystal located in the close vicinity to the rear flat mirror of first arm of Z-type resonator. The acousto-optic Q-switch with 40.7 MHz radio-frequency was located near flat output coupler. The two folding mirrors were mounted on the translation stages to enable matching the resonance frequency of the cavity to the modulation frequency of acousto-optic cell. Due to weak prelassing at 40.7 MHz frequency, the Q-switched pulse train has started to build up from ordered mode locked radiation. The QML pulses with envelope durations of 100-150 ns and near 100% modulation depth were observed for wide range of pump powers and repetition rates. Above 3 W of output average power, 0.130 mJ of the envelope energy having approximately 5-8 mode locked pulses were achieved. The maximum energy of mode locked pulse was about 0.03 mJ with pulse durations much less than 1 ns.
Optimization of a femtosecond Ti:Sapphire amplifier using an acousto-optic programmable dispersive filter and a genetic algorithm
Oleg J. Korovyanko, Roberto Rey-de-Castro, Christopher G. Elles, et al.
The temporal output of a Ti:Sapphire laser system has been optimized using an acousto-optic programmable dispersive filter and a genetic algorithm. In-situ recording the evolution of spectral phase, amplitude and temporal pulse profile for each iteration of the algorithm using SPIDER shows that we are able to lock the spectral phase of the laser pulse within a narrow margin. By using the second harmonic of the CPA laser as feedback for the genetic algorithm, it has been demonstrated that severe mismatch between the compressor and stretcher can be compensated for in a short period of time.
Tunable Lasers
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High performance widely tunable Ti:sapphire laser with nanosecond pulses
Design, theoretical modeling, and experimental characterization of a widely tunable Ti:Sapphire laser with nanosecond pulses and high pulse peak power is presented. The laser provides a continuous tuning range of from 675 nm to 1025 nm with no exchange of optics required. At a pulse rate of one kilohertz it delivers pulse energies of up to 2.5 mJ, pulse durations of around 20 ns, a spectral bandwidth of 10GHz and an almost diffraction-limited beam quality of M2<1.2 with a smooth characteristic of these parameters over the full wavelength range. This clearly exceeds the performance data published so far with our previous designs. Effects, which tent to provoke spectral gaps in the past, are totally understood and definitely suppressed by a modified resonator design. The presentation contains a detailed description and discussion of performance determining design aspects, i.e. pump scheme and pump beam shaping, resonator design and the comparison of different tuning elements. As a main prerequisite of an appropriate resonator design thermal lensing in Ti:Sapphire crystals is discussed on the basis of experimental and theoretical results. This includes the wavelength dependency of the focal length, the astigmatism in end-pumped Ti:Sapphire crystals with Brewster-cut end faces, the influence of the pump-light distribution and different cooling schemes.
Power scaling and extended tunability of mode-locked titanium-doped sapphire lasers
Stefan Marzenell, Richard D. Boggy, Ian A. Read, et al.
In this talk we first review the historical development of commercial mode-locked lasers based on titanium doped sapphire, including experimental and theoretical data highlighting the limits of these lasers, especially average output power and tuning range. Commercially available one-box systems are rapidly approaching these limits, with the latest systems offering an average power of more than 2.9W at 800nm, corresponding to more than 350kW peak power. In addition, systems are now becoming available with an extremely wide tuning range, extending from just under 700nm to over 1020nm, using only a single set of optics. These achievements enable further advancements of applications, such as micromachining, which require the highest peak power with increased throughput rates, and multi-photon microscopy where increased tunability and higher average power are of particular benefit. Some of the remaining challenges and the innovative techniques used to address them will also be discussed during the presentation.
High-efficiency CW green-pumped alexandrite lasers
J. W. Kuper, D. C. Brown
High power, CW and pulsed alexandrite lasers were produced by pumping the laser rod with a high quality diode pumped 532 nm laser sources. This pumping architecture provides stable performance with output power > 1.4 W at 767nm in the free running mode and 0.78W at 1000 Hz. An output of 80 mW at 375.5 nm was achieved at 500 Hz. This approach holds promise for the production of a scalable diode-pumped, tunable alexandrite laser systems operating in the near infrared (750 nm), and the ultraviolet (375 and 250 nm) spectral regions.
Characterization of cobalt-doped ZnSe and ZnS crystals as saturable absorbers for alexandrite lasers
Robert A. Sims, John Kernal, Vladimir V. Fedorov, et al.
Cobalt doped ZnSe and ZnS crystals have been studied to determine their effectiveness for passive Q-switching for 700-800nm spectral range (Alexandrite laser). Samples were prepared using Bridgeman technique for single-step growth of Co doped crystals as well as after growth thermal diffusion of Co in undoped crystals. ZnS:Co:Cr crystals, which have been produced using the Bridgeman technique, show maximum initial absorption coefficients of 17 cm-1 at 725nm. Experimental results are reported on effective thermal diffusion of Co2+ in ZnSe and ZnS polycrystals and thermal diffusion constants of cobalt ions in ZnSe and ZnS are estimated. The nonlinear saturation properties of cobalt doped ZnSe and ZnS crystals have been investigated experimentally. The induced transparency measurements were performed using electro-optically Q-switched, alexandrite laser radiation at 731, 741, and 778 nm with a pulse duration of about 70 ns. The induced transmission measurements were analyzed using a four-level absorber model and the absorption cross sections have been estimated at both 731nm and 741nm to be 9.5 × 10-18 cm2 and 8.2 × 10-18 cm2, respectively. Absorption cross sections calculated from saturation measurements at 4A24T1(4P) transition are in agreement with results earlier reported for mid-infrared spectral region 4A24T2 of Co2+ ions. The described Co-doped crystals are very promising as passive Q-switches for alexandrite laser resonators. Co2+ centers feature high cross section of saturation and their absorption bands are nicely matched to the spectral emission of the tunable alexandrite laser. An efficient ZnS:Co:Cr passive Q-switching of the alexandrite laser cavity was realized with output energy of 15 mJ and 50 ns pulse duration.
Construction and characterization of a titanium:sapphire CW laser system with kHz linewidth
S. Hädrich, P. Jauernik, L. McCrumb
Tunable, frequency stabilized lasers are essential for numerous precision measurements and experiments such as laser cooling. We report the construction of a titanium:sapphire laser system (called Matisse) that is designed to have a frequency bandwidth stability of 10-8 in 1 sec averaging. This level of accuracy is achieved by the use of unique mechanical features, careful choice of optical components and state-of-the-art active control. The system is comprised of a ring cavity, an intracavity electro-optic modulator, a digital signal-processor-based control unit and a reference cavity. Optionally, the output can be frequency doubled to extend the accessible wavelength range. We present data of the output energy achieved, tuning curves, beam parameters doubling efficiency, amplitude noise and spectral noise.
Laser Materials and Components
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Fluoride laser crystals: old and new
Hans P. Jenssen, Arlete Cassanho
The development of oxide and fluoride materials as gain materials of choice for solid state lasers ranges from early materials such as Calcium Fluoride and Calcium Tungstate crystals to the now ubiquitous Nd hosts YLF, YAG and Vanadate. Among Tunable laser materials, MgF2 - an early favorite, gave way to superior oxides such as Alexandrite and Ti:Sapphire only to be followed by development of still newer tunable fluoride media, notably, fluoride colquiriites such as Cr-doped LiSAF and LiCaF. Newer fluoride crystals, such as Barium Yttrium Fluoride BaY2 F8 (BYF), KY3F10 (KYF) and the tunable Cr doped LiCaGaF6 are attractive laser materials, but their growth has not been optimized. Key advantages of two of these new crystals are discussed. Crystal growth results for BYF and Cr:LiCaGaF6 as well as some material characterization are presented.
Modeling of time-dependent thermal effects in Cr2+-doped zinc selenide thin disks
We used finite element software to model the time dependence of thermal lensing and temperature rise in a Cr2+-doped zinc selenide thin disk for pulsed pumping. Two cases, chopped cw and Q-switched pumping, were considered. The model agrees well with experimental results for the chopped pumping case but does not directly agree with Q-switched pumping because the time delay between absorption and heat transfer to the host material is not accounted for in our model.
Middle-infrared electroluminescence of n-type Cr-doped ZnSe crystals
Lawrence Luke, Vladimir V. Fedorov, Igor Moskalev, et al.
We report the study of middle-infrared electroluminescence of n-type, Cr doped bulk ZnSe crystals. n-type, Cr-doped ZnSe samples were prepared in three stages. At the first stage, the undoped polycrystalline ZnSe samples were grown by chemical vapor deposition. During the second stage, the doping of 1 mm thick ZnSe polycrystalline wafers was performed by post-growth thermal diffusion of Cr. Finally, Cr:ZnSe wafers were annealed with Al2Se3 and ZnSe powders in sealed vacuumed ampoules at 950°C for 96 hours. Comparison of the absorption spectra of the crystals before and after thermal diffusion with Aluminum indicates the preservation of the desired Cr2+ ions. Ohmic contacts for electrical measurements were formed by polishing the facets and wetting the surface of the crystals with In. The best crystals demonstrated conductivity of up to 10-100 ohm*cm. The electroluminescence measurements were taken using synchronous detection methods with an InSb detector. A pulse generator output (100V) at 5 kHz and a lock-in amplifier were used to distinguish luminescence signals from other possible noise sources. We report the observation of middleinfrared (2-3μm and 8μm) and visible (~600 nm) electroluminescence of n-type Cr doped bulk ZnSe crystals.
Lasing properties of new Nd3+-doped tungstate, molybdate, and fluoride materials under selective optical pumping
The purpose of this work was to determine the relative efficiencies of new Nd3+-doped laser active/Raman - tungstate, molybdate, and fluoride - materials (SrWO4, PbWO4, BaWO4, SrMoO4, PbMoO4, SrF2, and LaF3) under selective longitudinal optical pumping by the alexandrite (~750nm), or diode (~800nm) laser. Crystals with various length, orientations and active ions concentrations were tested. To optimize the output of the tested lasers a set of input dichroic and output dielectric mirrors with different reflectivities were used. For realized lasers operating at pulsed free-running regime, threshold energy, slope efficiency, emission wavelength, and radiation polarization were determined. For each crystal, fluorescence lifetime and absorption coefficient under given pumping were established. The slope efficiency in case of Nd3+:PbMoO4 laser at wavelength 1054nm was measured to be 54.3% with total efficiency of 46% which is the best result obtained for all new tested crystals. For Nd3+ doped SrWO4, PbWO4, and BaWO4 crystals simultaneous laser and self-Raman emission were demonstrated in Q-switched regime. Thus newly proposed laser Raman crystals demonstrate high efficiency for Nd3+ laser oscillations comparable with well known and widely used Nd:KGW crystal. Further improvement in the quality of tungstate and molybdate type crystals should result in further increase in lasing efficiency at 1.06μm wavelength. Self Raman frequency conversion of Nd3+-laser oscillations in these crystals should result in high efficient pulse shortening, high peak power and new wavelengths in 1.2-1.5μm wavelength region.
Enhancement of blue thulium emission on Nd:Yb:Tm-doped YLF crystals
Lilia C. Courrol, Izilda M. Ranieri, Ricardo E. Samad, et al.
In this paper we present the spectroscopic properties of YLF:Yb:Tm:Nd system identifying the most important processes that lead to the thulium blue up conversion emission, under excitation around 792 nm. Analysis of the 475 nm emission for the samples with different concentrations of Nd3+ ions showed that energy transfer between Nd3+ and Yb3+ is the main mechanism and responsible for an enhancement in up conversion.
Spatial mapping of fluorescence and Raman spectra across grain boundaries in a transparent Nd-YAG ceramic laser material
Sang-Ho Lee, Joseph P. Stitt, William B. White, et al.
We present spatial mapping of fluorescence and Raman spectra across grains and grain boundaries in a transparent Nd-YAG laser material with 5 at% Nd- doping using confocal scanning optical microscopy. These signals do not show any significant spectral shifts, indicating exceptional compositional uniformity in the bulk and grain boundaries. Changes in the intensity of Raman and fluorescent signals between grains and grain boundaries are observed, arising primarily from scattering at the grain boundaries both in the interior and the surface of the ceramic.
Development of solid-state ceramic laser material using Nd:yttria
Narasimha S. Prasad, Sudhir B Trivedi, Susan Kutcher, et al.
In this paper, recent progress made towards the development of transparent Nd doped ceramic yttria is presented. Using 99.99% pure raw materials and with improved material processing techniques, Nd doped ceramic yttria test samples greater than 99% transmission at 2000nm wavelength and bandedge <250nm have been produced. The test samples were >1" x 1" x 10mm in dimensions. Nd ions were successfully incorporated into undoped ceramic yttria material through diffusion process.
Laser properties of mixed Nd:Y1-xGdx VO4 with different crystal compositions
Y. Tang, X. Wang, S. Tang, et al.
With Gd ions replacing a fraction of Y ions in Nd:YVO4 crystal, a new class of mixed gadolinium yttrium vanadate crystals Nd:Y1-xGdxVO4 is formed with adjustable laser parameters. As a result, a new laser crystal may be produced with optimized stimulated cross-section and fluorescence lifetime. In this paper, important laser parameters, such as material thermal properties, laser slope efficiency, and overall optical-to-optical efficiency, of new mixed vanadate crystals Nd:Y1-xGdxVO4 were investigated with different Nd doping levels as well as different yttrium and gadolinium composition ratios. Comparative studies will be presented in reference to better known laser crystals like Nd:YVO4 and Nd:GdVO4 crystals.
Compositional influence on spectroscopic properties of Yb3+-doped tellurite glasses
Márcio A. R. C. Alencar, Rogério F. Souza, Marcos V. D. Vermelho, et al.
Spectroscopic properties of ytterbium-doped tellurite glasses with different compositions are reported. Results of linear refractive index, absorption and emission spectra, and fluorescence lifetimes are presented. The studied samples present high refractive index (~2.0) and large transmission window (380-6000nm). Absorption and emission cross-sections are calculated as well as the minimum pump laser intensity. The results are compared with the values of other laser materials, in order to investigate applications as laser media in the infrared region.
High Power Lasers
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MOPA with kW average power and multi MW peak power: experimental results, theoretical modeling, and scaling limits
A Master-Oscillator-Power-Amplifier (MOPA) design combining rod and slab laser technology for high pulse energy, high average power and near diffraction limited beam quality for industrial use has been developed. To achieve the good beam quality at high average and high pulse power, an advanced birefringence compensation scheme, which ensures a high mode overlap while simultaneously minimizing the power densities on optical surfaces, has been developed and applied. The prototypes deliver an average power of up to 860 W with M2 < 2 or 1.3 kW with M2 < 12 at 10 kHz repetition rate and 5-16 ns pulse duration. At 1 kHz up to 420 mJ pulse energy can be achieved. The prototypes are fully computer controlled and can be operated from 0 to 100 % output power and from single shot to 10 kHz. They are currently operated for plasma generation in a laboratory surrounding and have run for more than one thousand hours without failure up to now. An analytical solution of the thermally induced refractive index profile in dependency of a radially symmetric pump light distribution including the effect of thermally induced birefringence, temperature dependency of the thermal conductivity and the second derivative of the refractive index with the temperature (d2n/dT2) has been derived. This allows a fast calculation of thermally induced aberrations without the use of FEA. Experimental results are compared to predictions from analytical and FEA modelling. Based on experimental and theoretical results, scaling limits of rod based MOPAs are predicted.
Improving the beam quality of a high-power Yb:YAG rod laser
An investigation has been made of improving beam quality of a high power diode pumped solid state rod laser. It was determined that the beam quality is limited by aberrations present in the medium, which may be due to mode-medium effects in the Yb:YAG laser. A diffractive optics propagation model was developed to predict the phase distortions present on the laser wavefront at the resonator mirror. Resonator mirrors were then fabricated with the proper correction applied to correct the distorted wavefront. The beam quality improved from M2 = 2.0 to M2 =1.4.
Harmonic Power Scaling
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High-power Q-switched TEM00 mode diode-pumped solid state lasers with > 30W output power at 355nm
Charles X. Wang, Gary Y. Wang, Acle V. Hicks, et al.
Since their first commercial introduction in 1997, diode-pumped Q-switched vanadate and YAG lasers with 355nm output have advanced in power level and reliability and are now qualified in many industrial processes, such as via hole drilling, stereo lithography, wafer scribing and dicing. At present, average output power of up to 20W at 355nm are commercially available with pulse energies of several hundred micro-Joules and pulse repetition rates of up to 150 kHz. In this paper, we report high power UV generation with TEM00 mode output powers in excess of 30W in Q-switched, end-pumped Nd:YVO4 and side-pumped Nd:YAG lasers using extra-cavity sum frequency generation in LBO. With a side-pumped dual-rod Nd:YAG rod oscillator and extra-cavity tripling, 32W output power at 355nm have been achieved at a repetition rate of 50 kHz. With an end-pumped vanadate MOPA configuration, UV average power of 36W with TEM00 mode was realized at repetition rates around 100 kHz. Lifetest results are presented and the scaling to higher UV power of more than 60W is discussed.
Advances in high-power harmonic generation: Q-switched lasers with electronically adjustable pulse width
Loren A. Eyres, James J. Morehead, Jeffrey Gregg, et al.
We demonstrate a variable pulse width, internally-frequency-converted, near-diffraction-limited Nd:YAG laser with output power up to 40 Watts at 532 nm and pulse widths electronically adjustable over a 40-300 ns range. The variable pulse width is achieved by clipping the pulse decaying edge with the Q-switch in a laser cavity optimized for post-pulse gain insensitivity. This approach makes possible frequency converted lasers with pulse width and output power substantially independent of repetition rate.
Frequency Converted Lasers (Joint Session)
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Generation of THz and IR radiation in DAST crystals
A. Schneider, M. Stillhart, P. Günter
Short THz pulses are commonly generated through the optical rectification of ultrashort laser pulses in nonlinear optical crystals. Our purpose is to discuss the controllability of the THz spectrum emitted from the polar organic salt DAST (4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate) and also the efficiency of the THz generation. It does not only depend on different experimental parameters such as duration of the laser pulse and crystal thickness, but is also affected by absorption and dispersion caused by several resonances of the crystal in the THz range.
200 Terawatt femtosecond laser based on optical parametric amplification in DKDP crystal
V. V. Lozhkarev, V. N. Ginzburg, G. I. Freidman, et al.
200 TW (pulse duration 45 fs at energy 9 J) peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.
New wavelengths generated by BaWO4 or KGW intracavity Raman laser
The paper deals with the generation of new infrared laser wavelengths (1.175 μm, 1.196 μm, and 1.199 μm) based on the intracavity Raman conversion of the Nd:YAP laser radiation (1.0796 μm). Barium tungstate (BaWO4) and potassium gadolinium tungstate (KGW) crystals were used as solid state Raman converters. The laser was based on three-mirror linear cavity forming resonator for fundamental (resonator lengths 126 mm) and Raman (resonator lengths 35 mm) radiation generation. As an active laser crystal Nd:YAP in the form of Brewster angle trigonal slab was used. This shape of the active medium enables constructing the simple linear laser cavity. For pumping of this crystal the QCW fast-axis collimated laser diode was used. To obtain high peak power in fundamental radiation, the Cr4+:YAG crystal was used for Q-switching. The Raman laser was optimized for maximal output energy at the first Stokes wavelength. A stable output was reached for both Raman crystals. In the case of BaWO4 crystal the output pulse (energy ~165 μJ, length of pulse 1.7 ns) with a wavelength of 1.199 μm was generated. The Raman generated wavelengths in the case of KGW crystal were 1.1756 μm and 1.1957 μm, depending on the orientation of the crystal inside the resonator. The output energy in the generated pulse with a length of ~1 ns (FWHM) was ~90 μJ for both orientations. The beam output structure was close to the fundamental mode with the divergence ~ 3-4 mrad. The efficient second harmonic generation giving possibility of new wavelengths generation in visible region was demonstrated.
Characterization of RbTiOPO4 crystal for non-linear and electro-optic applications
H. Albrecht, C. Bonnin, Y. Gromfeld, et al.
The aim of this work is to introduce the RTP material and point out its main fields of application for solid-state lasers, both in non-linear optics and electro-optics. The paper reviews the performance of the RTP crystals for visible and infrared frequency conversion. This review ends by covering the properties of RTP for electro-optics.
Mode locked Nd:YVO4 laser with intracavity synchronously pumped optical parametric oscillator
The motivation of this work is the development of laser sensor and gyroscope based on short pulse solid state ring laser. In comparison with regular ring laser containing the gain medium and saturable absorber, where counterpropagating pulses overlap, a ring synchronously pumped optical parametric oscillator, in which the pulse crossing point is controlled externally by the time of arrival of the pump pulses, is the ideal source for short pulse laser sensor. The optimum configuration is a synchronously pumped parametric oscillator inserted inside the optical resonator of the diode pumped mode-locked solid state laser. We are developing a such system, as a first step we have demonstrated operation of a diode pumped Nd:YVO4 passively mode-locked laser using semiconductor saturable absorber with synchronously pumped intracavity optical parametric oscillator in linear configuration. The repetition rate of the pump laser was 132 MHz and the pulse duration of 15 ps. Parametric oscillator was based on 20 mm long Brewster cut single grating (with poling periode of 30.3 μm) periodically poled magnesium doped lithium niobate (MgO:PPLN) crystal. The temperature tuning of parametric luminescence from the crystal with peak wavelength at 1537 nm - 1550 nm for temperature variation from 30 °C to 57 °C was observed.
Laser Systems Designs, Modeling, and Applications
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High-power solid-state sodium guidestar laser for the Gemini North Observatory
We report on the first successful installation of a commercial solid-state sodium guidestar laser system (GLS). The GLS developed at LMCT was delivered to Gemini North Observatory in February of 2005. The laser is a single beacon system that implements a novel laser architecture and represents a critical step towards addressing the need of the astronomy and military adaptive optics (AO) communities for a robust turn-key commercial GLS. The laser was installed on the center section of the 8 m Gemini North telescope, with the output beam relayed to a laser launch telescope located behind the 1 m diameter secondary mirror. The laser went through a three week performance evaluation between November and December 2005 wherein it consistently generated 12 W average power with measured M2 < 1.1 while locked to the D2 line at +/- 100 MHz. The system was required to perform during a 12-hour test period during three runs of 4-6 consecutive nights each. The laser architecture is based on continuous wave (CW) mode-locked solid-state lasers. The mode-locked format enables more efficient SFG conversion, and dispenses with complex resonant intensity enhancement systems and injection-locking electronics. The linearly-polarized, near-diffraction-limited, modelocked 1319 nm and 1064 nm pulses are generated in separate dual-head diode-pumped resonators. The two IR pulses are input into a single-stage, 30 mm PPSLT sum-frequency generation (SFG) crystal provided by Physical Science, Inc. Visible (589 nm) power of >16 W have been generated, representing a conversion efficiency of 40%.
Optical extraction from Nd:YAG lasers with ASE gain depumping losses
Optical extraction characteristics of steady-state solid-state Nd:YAG lasers with amplified spontaneous emission (ASE) gain depumping losses are discussed. The gain model includes gain depumping losses by ASE and assumes that the medium is homogeneously-broadened. The rate equations describing the spatial growth of the intracavity intensities for a stable optical resonator are summarized, the threshold lasing condition is derived, and the coupled equations solved for the optical extraction efficiency using both first-order perturbation theory and a new numerical method in which the two-point boundary value problem is recast as an integral equation to be solved for the geometric mean of the forward and backward intensities at the optic axis. Solutions are determined for the optical extraction efficiency for medium parameters appropriate to high gain Nd:YAG lasers. Comparisons with the simple, uniform intracavity intensity model show the latter is not always a good approximation. The well-established empirical critera that the gain-length product satisfy gℓ < 2-4 to limit ASE power losses is shown to be a consequence of a constraint arising to ensure the validity of a perturbation solution of the stable resonator model and its upper limit is shown to be determined by the spectroscopic and lifetime parameters of the gain media.
Modeling a diode pumped Nd: YAG rod laser
Hong Shu, Ying Chen, Michael Bass, et al.
We evaluate the performance potential of a diode pumped Nd: YAG rod laser by finding the absorbed pump distribution using ASAP, pump induced thermal lensing, gain medium surface distortion and stresses using FEMLAB and depolarization losses using MATLAB. Beam propagation in the optically distorted Nd:YAG rod and the free space part of the cavity, and the output laser beam were determined with a computational scheme we developed which employs the beam propagation method combined with sparse matrix technology. We propose a special cavity design that can select the spatial eigen mode shape of the laser and simultaneously compensate for pump induced thermal lensing, gain medium surface distortion and birefringence. The converged solutions calculated this special cavity design give both high extraction efficiency and good output beam quality. Sensitivity of the output beam to mirror tilt, thermal induced mirror distortion, and errors in the cavity length or the optical distortions in the rod were also calculated.
Comparative performance of passively Q-switched diode-pumped Yb:GGG, Yb:YAG, and Yb-doped tungstates lasers using Cr4+ -doped garnets
Y. Kalisky, O. Kalisky, U. Rachum, et al.
We investigated the CW free-running and repetitive modulation in the kHz frequency domain of a passively Q-switched, diode-pumped Yb:YAG, Yb:GGG and Yb:KYW lasers, by using Cr4+:YAG as a saturable absorber. The results presented here are focused towards the design of a passively Q-switched Yb doped garnets or Yb doped tungstates microlaser. The free-running performance of Yb:YAG, Yb:GGG, Yb:KGW and Yb:KYW were characterized, and experimental parameters such as gain and loss were evaluated. We carried out a fit between our experimental results and an existing numerical model, which relates the experimental and the physical parameters of the ytterbium diode-pumped system to the minimal threshold pumping power. The best performance among the laser crystals was obtained for Yb:YAG laser. A maximum peak power of ≈4.5-kW, at an average output power of 1.32-W, were extracted with of ≈25 % extraction efficiency.
Side-pumped neodymium slab lasers Q-switched by V:YAG on 1.3μm
Nd:YAG and Nd:YAP crystals in form of triangle which makes possible to realize a slab side-pumped configuration with one total internal reflection were tested as an active media for diode-pumped laser. The resonator arrangements for Q-switched regime were prepared for the emission corresponding to Nd3+ ion transition 4F3/24I13/2 referring to each crystal (λ= 1318 nm Nd:YAG and λ= 1342 nm Nd:YAP). Optical pumping was accomplished by a fast axis collimated quasi-CW diode DILAS E7Y1-808.3-600Q-H175V with peak power 600 W. Pumping radiation was focused by two plan-convex lenses into an active medium. The parameters of the pumping radiation were: wavelength 806nm, maximum pumping energy was 150mJ, pulse length 250μs, repetition rate up to 14 Hz. In free running regime the maximum reached energy was 24 mJ and 27.5 mJ for Nd:YAG and Nd:YAP, respectively. The corresponding obtained slope efficiency was 19.9 % and 23.7 % for Nd:YAG and Nd:YAP laser oscillator, respectively. Proper Q-switching for 1.3 μm was realized with saturable absorber V:YAG which initial transmission was optimized for shortest possible pulse length. For that obtained pulses were 6 ns with the energies 740 μJ and 432 μJ for Nd:YAG and Nd:YAP, respectively. This results correspond to peak power reached 125 kW (Nd:YAG), and 77 kW (Nd:YAP) in fundamental TEM00 mode which allows this laser to be used as an efficient source for further nonlinear conversion or other applications.
High-power Q-switched rotary disk lasers
Santanu Basu, Bryan Norton
Rotary disk laser has a very efficient thermal management approach that uses physical motion of the gain medium in a diode-pumped solid state laser. The benefits of rotary disk lasers over conventional bulk solid state lasers are high efficiency, power scalability and high peak power pulsed operation in a single-mode output beam. We have generated 72.8 W of TEM00 Qswitched output power at 50% slope efficiency in a crystalline Yb-YAG rotary disk laser.
Tailoring the performance of q-switched solid state lasers: why and how
Stephan Geiger
Diode-pumped, solid state, q-switched lasers now enable a very diverse array of precision materials-processing applications. An important key to ongoing market growth and applications diversification is the development of lasers whose performance is optimally tailored to meet the needs of specific applications. For example, long output pulses are preferable for soft wafer marking, whereas short pulses are desirable for solar cell scribing and creating gray-scale pictures for passports and other personal identity applications. The pulsewidth and overall output power are interdependent performance characteristics determined by laser design parameters such as resonator length, repetition rate, and pumping intensity. This interdependence leads to trade-offs when optimizing the laser performance, meaning that no single resonator configuration can simultaneously meet the needs of all applications. This paper reviews the basics of q-switched, diode-pumped laser operation, and examines some of their most important applications in terms of performance requirements. We then present a modular laser design approach that enables niche markets and prototype applications to be serviced with optimum performance, without incurring significant costs for custom laser development.
Diode-end-pumped actively and passively Q-switched Nd:GdVO4 lasers at 1.34 μm
Chenlin Du, Shuangchen Ruan, Huaijin Zhang, et al.
With an acousto-optical Q-switch and Co:LaMgAl11O19(Co:LMA) crystal as the saturable absorber, diode-end-pumped actively and passively Q-switched Nd:GdVO4 lasers at 1.34 μm were demonstrated, respectively. For acousto-optical Q-switched operation, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 4.54 W, 223 μJ, 19 ns and 11.75 kW, respectively. For passively Q-switched operation with a 0.3-mm-long Co:LMA crystal as the saturable absorber, the maximum average output power, the highest pulse energy, the shortest pulse width and the highest peak power were obtained to be 1.43 W, 112 μJ, 55 ns and 1.95 kW, respectively.
Novel laser range finding algorithms
Junewen Chen, Mau-Shiun Yeh
Novel laser range finding algorithms and a single element laser range finder transceiver modular component have been developed and put in practical use. The laser range finder measure up to 60 m maximum and with resolution of 1 to 3 mm. Multi-modulation frequencies high resolution ranging algorithms first use only a lower or medium frequency to obtain the non-ambiguity range (NAR), and then by using higher relative frequency with locked phase, we can obtain high resolution ranging results.
Extractable energy from ytterbium-doped high-energy pulsed fiber amplifiers and lasers
Yoav Sintov, Ori Katz, Yaakov Glick, et al.
An analytic model is developed for evaluating the extractable energy from high energy pulsed Ytterbium doped fiber amplifiers and lasers. The energy extraction capabilities under the limitation of spurious lasing, due to amplified spontaneous emission (ASE), are mapped for various numerical apertures, single and multi transverse mode evolution and operating wavelengths. The calculation results of the analytic model show good match with experimental results carried out for various double clad fiber amplifiers. The model provides an accurate assessment for the maximum pulse energy that can be extracted from a given Ytterbium doped fiber. In addition, for a specific pump power, the model can be used to determine the minimum repetition rate and optimal length, under which the laser source can be operated before spurious lasing occurs.
Special Session: Space Qualified Laser Components and Systems I
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Review of solid-state lasers for space applications (Tutorial)
Robert S. Afzal
Solid-state lasers have been in use for space applications since the early days of the space program. To date most of the lasers have been pulsed Nd:YAG lasers and with the development of diode laser technology as pump sources, performance improvements in lifetime, weight and efficiency have been the key drivers to enable space missions. This paper will review the lasers used on various missions and discuss their designs and performance in light of their mission requirements.
Qualification and issues with space flight laser systems and components
The art of flight quality solid-state laser development is still relatively young, and much is still unknown regarding the best procedures, components, and packaging required for achieving the maximum possible lifetime and reliability when deployed in the harsh space environment. One of the most important issues is the limited and unstable supply of quality, high power diode arrays with significant technological heritage and market lifetime. Since Spectra Diode Labs Inc. ended their involvement in the pulsed array business in the late 1990's, there has been a flurry of activity from other manufacturers, but little effort focused on flight quality production. This forces NASA, inevitably, to examine the use of commercial parts to enable space flight laser designs. System-level issues such as power cycling, operational derating, duty cycle, and contamination risks to other laser components are some of the more significant unknown, if unquantifiable, parameters that directly effect transmitter reliability. Designs and processes can be formulated for the system and the components (including thorough modeling) to mitigate risk based on the known failures modes as well as lessons learned that GSFC has collected over the past ten years of space flight operation of lasers. In addition, knowledge of the potential failure modes related to the system and the components themselves can allow the qualification testing to be done in an efficient yet, effective manner. Careful test plan development coupled with physics of failure knowledge will enable cost effect qualification of commercial technology. Presented here will be lessons learned from space flight experience, brief synopsis of known potential failure modes, mitigation techniques, and options for testing from the system level to the component level.
Space qualification issues in acousto optic tunable filter (AOTF) based spectrometers
Sudhir Trivedi, Jolanta Rosemeier, Feng Jin, et al.
AOTF spectrometers have found useful role in space exploration due to their ruggedness, tunability and absence of moving parts. We discuss their space qualification issues.
Qualification of the laser transmitter for the CALIPSO aerosol lidar mission
Space-based missions impose a unique set of requirements on laser designs. The development of the CALIPSO Laser Transmitter Subsystem (LTS) began with a successful lifetime test using the Risk Reduction Laser (RRL), followed with an intensive design validation phase using prototype flight hardware, and completed with formal qualification of the flight hardware. We will describe this process in more detail and review the issues encountered and lessons learned. From this experience we developed a set of guidelines for designing and building future space-based lasers.
Overview of qualification protocol of fiber lasers for space applications
Sami Hendow, Suzzanne Falvey, Burke Nelson, et al.
There are many applications where fibers are employed in space, such as fiber gyros and fiber sensors. Fiber lasers are becoming increasingly attractive for space for similar reasons, which are lightweight, small size and low power consumption. The majority of components used in such systems are commercial off-the-shelf parts that have been developed using technologies similar to those used in the development of parts for the fiber telecom market. Space however has environmental conditions that require further hardening of these parts. Accordingly, a generic qualification protocol is suggested for qualifying generic parts for space flight. This protocol is based on merging the qualification requirements for telecom, such as those by Telcordia, with the qualification for spaceflight, such as by NASA. A set of components (at 1064 nm) is chosen for testing the protocol. These include doped fibers, combiners, sources, pumps, isolators and fiber Bragg gratings. The scope of the vibration, thermal and radiation tests used to validate the protocol is limited to the environmental conditions of lower Earth orbit satellites, 100 to 1000km orbital altitude and up to 60 degrees inclination. Also presented in this paper is a summary of a thorough survey conducted for publications related to space qualification of fibers and lasers for space.
Performance of the GLAS laser transmitter
Robert S. Afzal
The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results and in-flight performance for this space-based remote sensing instrument is summarized and presented.
High efficiency passively Q-switched Nd:YAG MOPA for spaceborne laser-altimetry
Dietmar Kracht, Sven Hahn, Rafael Huß, et al.
For the spaceborne laser-altimeter (BELA) of ESA's BepiColombo mission a master-oscillator-power-amplifier system (MOPA) is presented. The specified system-requirement is a pulsed laser source with a nearly diffraction limited beam (M2 < 1.6) that combines high pulse energy of about 50 mJ at less than 10 ns pulsewidth and up to 20 Hz pulse repetition rate with the stringent environmental conditions at space missions. A low-mass (< 1.3 kg) and high optical-to-optical efficiency (> 15 %) laser setup is required. Stable operation at a temperature range of at least 25 K for the MOPA system and 15 K for the pump diodes has to be guaranteed. Both oscillator and amplifiers are longitudinally pumped by fiber coupled QCW laser diodes. The performance of a longitudinal pumped system is, because of the longer absorption path, less sensitive to pump wavelength variations due to temperature changes of the laser pump diodes. The pump-pulse duration of 200 μs represents as a trade-off between output energy and efficiency of the whole system. The Nd:YAG oscillator was passively Q-switched with Cr4+:YAG crystal as a saturable absorber. With 100 W of peak pump power a nearly diffraction limited (M2≈ 1.2) laser pulse with a duration of 2.8 ns and a pulse energy of 2.4 mJ was generated. The output beam of the oscillator was amplified in a two stage amplifier. A maximum of 62 mJ pulse energy was achieved by pumping each crystal with a peak pump power of 600 W.