This PDF file contains the front matter associated with SPIE Proceedings Volume 7193, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months. In this paper, a few laser and optical elements from NASA Langley Research Center (LaRC) that have been flown on MISSE 6 mission will be discussed. These items were characterized and packed inside a ruggedized Passive Experiment Container (PEC) that resembles a suitcase. The PEC was tested for survivability due to launch conditions. Subsequently, the MISSE 6 PEC was transported by the STS-123 mission to International Space Station (ISS) on March 11, 2008. The astronauts successfully attached the PEC to external handrails and opened the PEC for long term exposure to the space environment. The plan is to retrieve the MISSE 6 PEC by STS-128 mission in August 2009.

NASA Goddard Space Flight Center (GSFC) has been engaging in Earth and planetary science instruments development for many years. With stunning topographic details of the Mars surface to Earth's surface maps and ice sheets dynamics of recent years, NASA GSFC has provided vast amount of scientific data products that gave detailed insights into Earth's and planetary sciences. In this paper we will review the past and present of space-qualified laser programs at GSFC and offer insights into future laser based science instrumentations.

The Lunar Orbiter Laser Altimeter (LOLA) is one of seven instruments aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft with the objectives to determine the global topography of the lunar surface at high resolution, measure landing site slopes and search for polar ices in shadowed regions. The LOLA laser transmitter is a passively Q-switched crossed-Porro resonator. All components used in the laser have space flight heritage. The flight laser bench houses two oscillators (a primary and a cold spare) that are designed to operate sequentially during the mission. If the primary laser can no longer provide adequate scientific data products, the secondary laser will be turned on. The baseline mission calls for LOLA (and LRO) to spend about one year studying the Moon. Since LOLA operates at 28 Hz, the laser system needs to produce approximately one billion pulses during the primary one year mission. To validate that the LOLA laser design is capable of meeting this requirement, the LOLA Engineering Model (EM) laser has been subjected to extended operation testing in vacuum. In this paper we will summarize the longevity validation test effort of the LOLA EM laser.

In the recent past, NASA's space-borne laser missions have been dominated by low repetition rate (<100Hz), Q-switched Nd:YAG lasers pumped by quasi-continuous wave (QCW) 808 nm laser diode arrays (LDA). QCW LDA reliability data is limited and their mechanisms of failure is poorly understood. Our group has been working in gathering statistically significant data on these devices and have developed testing strategies to achieve mission success in a cost-effective manner. In this paper, we present our approach for qualifying the LDAs for the Lunar Orbiter Laser Altimeter (LOLA) instrument scheduled to launch aboard the Lunar Reconnaissance Orbiter (LRO) mission. We describe our strategy to mitigate risk due to LDA failure given cost and schedule constraints. The results from extended testing of multiple LDAs in air and in vacuum are also presented.

The direct side-pumping of Nd:YAG rods with laser diodes has been shown to be a cost effective scheme for scaling to simultaneous high average and high peak power operation. Careful control of the parameters that govern the performance of a multi-spatial mode MOPA system has led to the demonstration of reliable Q-switched average powers of up to 1600 W and peak powers in excess of 18 MW at the 1064 nm fundamental wavelength. The techniques used to refine the properties of an infrared stable resonator in order to optimise intra-cavity second harmonic generation are discussed. Average powers of up to 290 W and peak powers of up to 0.45 MW at 532 nm have been demonstrated from a single cavity. By polarisation multiplexing the outputs of two cavities emitting at 532 nm, we have achieved single-beam average and peak powers of up to 580 W and 0.9 MW respectively and gained flexible control of pulse duration and temporal shape.

Performance data of a gain switched Ti:Sapphire laser operating at a repetition rate of one kilohertz is presented. With one single set of optics the tuning range of the laser exceeds 400 nm. The output power is 4.2 W at 800 nm with an almost diffraction limited beam quality and a pulse duration of 8 ns. The laser control includes two operational modes: Running the laser precisely at a certain wavelength or alternatively scanning the output wavelength continuously throughout a chosen band. Thanks to its high pulse peak power, narrow line width and high beam quality, this laser is well suited for frequency conversion.

We reported all-solid-state double Nd:YLF and Nd:YAG slab laser and their efficient frequency doubling in near field. With two Nd:YLF slabs fundamental laser pulse energy of 24 mJ and 15mJ pulse energy at 523 nm were obtained at a 1.0 kHz repetition rate. The pulse length at 1047nm and 523 nm was 7.1ns and 5.5 ns. The peak power is around 3MW. The corresponding conversion efficiency was 62.3%. With two Nd:YAG slabs average q-switched fundamental output of 169 W at 10 KHz was obtained. 93 W of second harmonic at 10 KHz with a pulse width of 10.7 ns was achieved. The efficiency of SHG was up to 57%.

The PCI technique, a modification of photothermal spectroscopy, has become a powerful tool for testing various low absorptive optical materials and components. The current state of the technique and recent progress in extending its capabilities toward the mid-infrared region is presented. A 3.39 μm probe was used for testing and studying various semiconductor materials, such as p-doped GaAs, that can exhibit non-thermal response to the pump beam in addition to the thermal one. A simple theoretical model of the PCI method is shown to describe adequately the experimental data, making it possible to calibrate the setup without using a calibration standard.

The objective of the Materials International Space Station Experiment (MISSE) is to study the performance of novel materials when subjected to the synergistic effects of the harsh space environment for several months. In this paper, a few laser and optical elements from NASA Langley Research Center (LaRC) that have been flown on MISSE 6 mission will be discussed. These items were characterized and packed inside a ruggedized Passive Experiment Container (PEC) that resembles a suitcase. The PEC was tested for survivability due to launch conditions. Subsequently, the MISSE 6 PEC was transported by the STS-123 mission to International Space Station (ISS) on March 11, 2008. The astronauts successfully attached the PEC to external handrails and opened the PEC for long term exposure to the space environment. The plan is to retrieve the MISSE 6 PEC by STS-128 mission in August 2009.

Fiber-to-fiber coupling between two different fibers is a state of the art technology. Products are available on the market where multimode fibers can be coupled with very low power loss, at very high powers (multi-kilowatt). We have, however, always been forced to accept a certain loss in beam quality, manifesting as an increase in the Beam Parameter Product (BPP). In fundamental-mode fiber-to-fiber coupling no beam quality is lost. We instead expect to have a certain power loss in the coupling. This paper addresses the problems in free-space fundamental-mode fiber-to-fiber coupling, including theoretical estimations of expected power loss, estimated demands on the stability of the optics as well as measured values on a fundamental mode fiber-to-fiber coupler. The theoretical calculations of the sensitivity of the coupling efficiency due to radial misalignment and defocus (longitudinal displacement) have been confirmed experimentally. Experimental results at 100 W laser power include 88% coupling efficiency using a large mode area fiber with mode-field diameter (MFD) of 18 μm and 75 % coupling efficiency using a single-mode fiber with MFD of 6.4 μm.

We present results from diode-pumped cw and semiconductor saturable absorber mirror (SESAM) mode-locked resonators containing multiple bulk Yb:KYW crystals. The dual-crystal resonator generated more than 24W of cw-power at a wavelength of 1042nm in a diffraction limited beam with the maximum power limited by the available pump power. Two mode-locking regimes were explored. From the soliton mode-locked oscillator we obtained Fourier limited pulses with a pulsewidth of 450fs at a repetition rate of 79MHz and with an average power of 14.6W. When operating the same resonator in the positive dispersion regime we achieved an output power of 17W. Using a grating compressor these pulses could be compressed to a pulse width of 470fs. Both mode-locked lasers were self-starting and operated stably and in turn key fashion over days and through varying lab conditions. Regarding the power scaling of this type of laser we anticipate further scalability by once again doubling the number of crystals inside the resonator.

We demonstrated for the first time three-level operation at 981 nm with a Yb:KYW crystal inserted into the cavity of a diode pumped Nd:YVO₄ laser operating at 914 nm. We achieved an output power up to 1.4 W at 981 nm. Moreover we demonstrated that crystal heating favored laser emission at 981 nm rather than emission at higher wavelength.

The Innoslab design, already established for neodymium doped laser materials, was applied to ytterbium doped laser materials. Recent progresses in brightness of high power diode lasers facilitate efficient pumping of quasi-three-level laser materials. A compact diode-pumped Yb:YAG Innoslab fs-oscillator-amplifier system, scalable to the kilowatt range, was realized. Nearly transform and diffraction limited 682 fs pulses at 400W average output power and 76 MHz repetition rate at room temperature and without using CPA technique have been achieved so far.

Recent developments of the micro-pulling down technique lead to efficient laser demonstration with Nd:YAG single crystal fibers. Indeed these media which benefit from the spectroscopic and thermal properties of bulk crystals and from the thin and long shape of glass fibers are ideal candidates for high average and high peak power laser systems. In this work, we investigate the potential of Yb:YAG single crystal fibers. After a careful design taking into account the quasithree level structure of the Yb³⁺ ions, we grew single crystal fibers by the micro-pulling down technique. With a 1 at.% doped and 40 mm long single crystal fiber of 1 mm in diameter, we obtained a power of 50 W in CW operation under 200 W of incident pump power. In the Q-switched regime, we achieved pulses with an energy of 1.8 mJ at 5 kHz and a duration of 13 ns for 120 W of pump power. We measured a M² value below 2.5. We also investigated the thermal management of our system by the use of thermal cartography and Finite Element Analysis, showing a maximum temperature smaller than 120°C reached on the pumped end face for 200 W of pump power. These results are a very promising to design high average power and high peak power laser sources.

We comparatively studied laser performance in the mixed vanadate crystals Nd:Y_xGd_1-xVO₄ with direct and indirect pumping. The maximum CW output power at 1064 nm was measured to be 6.6 W with 12 W direct 880 nm laser diode pumping, and 4.4 W with 8.8 W indirect 808 nm pumping. The optical conversion efficiency depended on the mixture ratio (x), pumping wavelength (direct or indirect), and pumping power. The hightest optical efficiency of 59% and slope efficiency of 74% were achived.

We present for the first time a frequency doubled Nd:GdVO₄ laser operating in continuous wave on the pure three-level laser line at 880 nm. We obtained 300 mW at 440 nm for 23 W of incident pump power at 808 nm. Moreover, an output power of 1.9 W has been obtained at 880 nm.

Nd:YVO₄ is widely and commercially available laser material for diode-pumped lasers. Compared to Nd:YAG, Nd:YVO₄ has a larger stimulated emission cross-section, larger absorption coefficient and broader absorption bandwidth. It has lower threshold and its output power is less sensitive to the drifting of the diode pump wavelength. In this paper a Nd:YVO₄ crystal at 1064nm pumped with a high power diode laser at 808nm is modeled and simulated using LasCAD software tool package. These models investigate the optimum cavity design parameters (length of the cavity, output coupler reflectivity, the beam overlap key parameter and crystal dimensions). The geometry of the cavity is optimized to produce maximum TEM₀₀ laser output, taking into consideration the thermal gradient on the rod structure. The cavity optimum configuration neglecting the insignificant effect of changing rod length was; 66mm in length, 90% of output coupler reflectivity. The pumping beam spot size affects on the laser output and the final optical conversion efficiency. Controlling the pumped spot size (w_g) to be equal the mode spot size (w_g) the maximum beam overlap efficiency and consequently the maximum optical slope efficiency with the highest laser output were achieved. The Nd:YVO4 Crystal with dimension of (1-3mm) diameter and (7-10mm) length with 1% doping concentration (1at.%) is the suitable choice for the DEPSS (Diode End Pumped Solid State ) laser configuration. A final optical conversion efficiency of 52% and a maximum slope efficiency of 54% were obtained.

It is well known that intra-cavity second-harmonic generation (SHG) suppresses mode hopping in solid-state resonators producing single-longitudinal-mode (SLM) output at the second-harmonic frequency (SHF). A simple extension of this concept is to suppress mode hopping in a resonator producing SLM output at the fundamental frequency (through an output-coupling mirror) by inserting an intra-cavity SHG crystal that converts a fraction of the intra-cavity power to the SHF. The beam at the SHF can either be dumped or is available as a second output beam. When combined with a PZT-actuated mirror, it is possible to continuously tune the frequency of the fundamental beam through a significant fraction of the gain bandwidth without mode hopping. SHG also suppresses mode hopping during warm up and during pumppower changes. These features were demonstrated in a unidirectional Nd:YVO₄ ring resonator producing an output beam greater than 25W at 1064nm while generating a few Watts at the SHF of 532nm. Mode hopping is substantially reduced during warm up and mode-hop-free operation can be sustained over many hours. Frequency tuning over several GHz was demonstrated and larger tuning ranges are possible. The PZT-actuated mirror can be used to eliminate frequency drift, to stabilize the output to a frequency standard (such as an atomic-absorption line), or to mitigate cavitylength changes due to acoustic noise.

The orthovanadate crystals YVO₄, GdVO₄, and LuVO₄ attract much attention as promising host materials for the trivalent Yb-ion since such crystals are characterized by large absorption and emission cross sections, broad absorption and emission bands, and higher thermal conductivities than most of the other Yb-doped materials. More interestingly, their laser operation is characterized by optical bistability, apparently a unique feature of Yb-doped vanadates, not found so far in other Yb-lasers or even in other solid-state lasers. The optically "passive" vanadates, YVO₄, GdVO₄, and LuVO4, as well as the stoichiometric YbVO₄ exhibit the same zircon structure and continuous isostructural solid solutions can be expected. The absorption and emission spectra of Yb_0.0054:Y_0.3481Gd_0.6465VO₄, a specific compound in the mixed Yb_t:Y_xGd_1-x-tVO₄ series, inherit the spectroscopic features of both Yb:YVO₄ and Yb:GdVO₄. We found that this Yb-doped solid solution also displays optical bistability in continuous-wave (cw) laser operation. The strongly pronounced bistability extends from P_abs=1.9 W to P_abs=3.4 W while the output power amounts to 0.98 W at the upthreshold. Distinct from the previously reported Yb:LuVO₄ laser, coexistence and switching of the σ and π polarization states occur along with emission wavelength shift in the bistability region upon decreasing the pump power. Increasing the output coupling reduces the bistability region while expanding the coexistence region for the σ and π polarization states.

We describe the design and performance of a high-peak-power, ns-pulsed, tunable OPO/OPA light source. The use of a volume Bragg grating output coupler in a 532-nm-pumped, singly-resonant KTP OPO provides stable, narrow-band (< 2-cm^-1) and frequency-tunable generation of light in the vicinity of 1 micron. Subsequent phase-coherent amplification of the signal-wave pulses in a single-pass, 532-nm-pumped KTP OPA provides >20 dB gain (up to 15 mJ pulse energy and 3 MW peak power). One frequency-doubled unstable-resonator Nd:YAG laser provides pump light for both OPO and OPA. The amplified signal wave is single-pass frequency-doubled to the blue-green in non-critically-phase-matched LBO, and frequency-doubled to the ultraviolet in critically-phase-matched CLBO, with efficiencies exceeding 50% and 25%, respectively.

This paper discusses the realization of an injection-seeded single frequency Q-switched Nd:YAG ring laser with pulse width adjustability from several nanoseconds to 20 ns and an output energy in excess of 100 mJ from a ring cavity slave oscillator. In the cavity configuration under study, the slave ring oscillator was injected by a pulse formed from a CW single frequency non-planar ring oscillator (NPRO) Nd:YAG laser with a Pockels cell modulator. The injected pulse duration is slightly shorter than the emission round trip time inside the slave laser cavity. The use of this injection seeding results in unidirectional Q-switched laser oscillation with suppression of bidirectional Q-switched oscillation that otherwise may be initiated from spontaneous emission. The advantage of these regime is in stable laser operation with no need in adjustment of the seeded light wavelength and the mode of the cavity because there are never two waves of the same polarization existing inside the cavity at the same location and the same time. The cavity contains two Pockels-cells, in which the first cell serves to open the oscillator cavity and the second one performs cavity dumping, generating a pulse with optimized characteristics and enables variation of the duration of the Q-switched output pulse. Proper selection of the pump parameters and Pockels-cell gating enables further operation of the system in a mode when the Q-switched pulse can be formed only under the seeding conditions. It is found that the wavelength of the Q-switched laser radiation matches well to the injected seed NPRO laser longitudinal mode. By using two-stage amplifiers, an output energy better than 300 mJ has been achieved in a MOPA configuration without active control of the cavity.

Single-frequency waveguide lasers are very promising candidate for applications were insensitivity to technical noise and possible integration with other devices are key issue. However for applications such as airbone radar and LIDAR output power of the order of 100 mW at a eye-safe wavelength is required. In this paper we propose a suitable way to build high-power robust single-frequency waveguide lasers at 1.5 micron and we demonstrate up to 80 mW with 40% efficiency in an almost single-frequency operation.

Eye-safe, high power tunable narrow linewidth lasers are important for various applications such as atmospheric propagation measurements. We have investigated two techniques of generating narrow linewidth thulium 2-μm fiber lasers, utilizing a reflective volume Bragg grating (VBG), and a guided mode resonance filter (GMRF) as a cavity end mirror. A stable narrow linewidth (50 pm), tunable (from 2004 nm to 2054 nm) thulium doped fiber laser using a reflective VBGg was demonstrated. A CW power of 17 W was achieved. Using a GMRF as an end mirror we showed a narrow linewidth (~30 pm) laser with an output power of 5.8W, and at a slope efficiency of 44%.

We have developed a self-aligned external cavity laser with a non-dispersive volume holographic grating (VHG) as the output coupler. The resulting external cavity is tunable by rotating the VHG. We have demonstrated tunable single mode longitudinal operation at 405 nm and 785 nm wavelength. The passive alignment of the novel tunable laser is the main driver for achieving low cost manufacturing. The axial symmetry enables the use of axially symmetric components such as TO-can laser packages, lenses and VHGs which further reduces the cost of manufacturing and the laser footprint.

High power compact UV lasers with diffraction limited beam are required for industrial applications such as laser direct imaging, wafer inspection or photo voltaic. By use of a Nd:YVO₄ oscillator with a Saturable Bragg Reflector and a single pass amplifier, 73 W output power in mode-locked operation at 80 MHz have been generated with high peak power. By use of two LBO crystals a third harmonic output power of 35 W at 355 nm was demonstrated with an M² value of <1.2. This corresponds to 48% nonlinear conversion efficiency.

We have developed a 389-nm frequency-doubled nanosecond-pulsed coherent light source with injection seeding for nuclear polarization of ³He atoms with 2³S→3³P and then suggested four kinds of spectroscopic methods with the injection-seeded light source. With this light source, we have conducted saturated absorption spectroscopy of metastable ³He atoms. As a result, an accurate resonance frequency of 770682 GHz and a dip width of 1.7 GHz of metastable ³He atoms are obtained. Therefore, the linewidth of our injection-seeded light source can be estimated at 65 MHz or 1.7 GHz. Our light source has potential for the polarization of ³He due to high-peak power and narrow linewidth of the injection-seeded light source.

An Innoslab based Nd:YV04 MOPA system with pulse energy of 7.25 mJ at 40 kHz repetition rate and pulse duration of 11.4 ns has been used for third harmonics generation in Lithium Triborate (LBO) crystals. We report UV pulses of 8.9 ns duration at pulse energy of 1.65 mJ, which means an average power of 66 W. We have been able to show UV beam qualities (M²) of 1.7/2.4 (stable/instable direction with 90/10 knife edge method), while IR beam quality is 1.8/5.2. A sinc²-shape transversal distribution of beam intensity has been used in instable direction of the Innoslab MOPA system for conversion. Due to high average power and short pulse length at 355 nm the laser meets the demands for high-throughput micro material processing as stereolithography or edge isolation of solar cells. The thermal dependence of the conversion efficiency (due to heating power of the beam) has been investigated theoretically, using a time resolved numerical simulation model for the nonlinear process in both LBO crystals. Scaling effects of the absorption coefficients of LBO and the pulse power on the conversion efficiency are presented in this article.

Intra-cavity harmonic generation in diode-pumped Q-switched Nd:YAG rod lasers is a preferred architecture to generate high output power at 532nm and 355nm in multimode operation. We have developed a side-pumped, dual rod Nd:YAG laser with intra-cavity second harmonic generation using Type II LBO in a double-pass configuration. A maximum 532nm output power of 420 W was achieved at 10 kHz with an M^2 of about 24. The pulse duration was 70 ns with a pulse energy stability of less than 0.7% rms. By incorporating a novel birefringence compensation technique and adding a Type II LBO sum frequency generator, we attained 160W of 355nm output at a repetition rate of 8 kHz with an M^2 of 18 and a pulse duration of 45 ns.

Many applications exist for high performance lasers in the short-wave, mid-infrared spectral regime between 1.9 and 2.5μm - from long-range communications systems through to remote atmospheric gas sensing and pollution monitoring. However, a simple, efficient laser source offering the desired performance characteristics and flexibility has not been available. In the last few years considerable progress has been made in the development of optically-pumped (AlGaIn)(AsSb) quantum well semiconductor disk lasers emitting in the 2.Xμm mid-infrared spectral region - continuous-wave and pulsed-pumped output power levels now exceed 6W and 16W respectively. Furthermore, singlefrequency operation with linewidths <4MHz and broad tunability of up to 170nm have also been demonstrated, all at near-diffraction-limited beam quality. Such performance metrics are only possible through the very best materials growth, a sound understanding of the design principles of these highly multi-layered devices and, importantly, the application of effective thermal management.

Design of optimized semiconductor optically-pumped semiconductor lasers (OPSLs) depends on many ingredients starting from the quantum wells, barrier and cladding layers all the way through to the resonant-periodic gain (RPG) and high reflectivity Bragg mirror (DBR) making up the OPSL active mirror. Accurate growth of the individual layers making up the RPG region is critical if performance degradation due to cavity misalignment is to be avoided. Optimization of the RPG+DBR structure requires knowledge of the heat generation and heating sinking of the active mirror. Nonlinear Control Strategies SimuLase^TM software, based on rigorous many-body calculations of the semiconductor optical response, allows for quantum well and barrier optimization by correlating low intensity photoluminescence spectra computed for the design, with direct experimentally measured wafer-level edge and surface PL spectra. Consequently, an OPSL device optimization procedure ideally requires a direct iterative interaction between designer and grower. In this article, we discuss the application of the many-body microscopic approach to OPSL devices lasing at 850nm, 1040nm and 2μm. The latter device involves and application of the many-body approach to mid-IR OPSLs based on antimonide materials. Finally we will present results on based on structural modifications of the epitaxial structure and/or novel material combinations that offer the potential to extend OPSL technology to new wavelength ranges.

Phase aberrations play an important role in shaping the beam and in determining the losses of laser resonators. An efficient method is presented for modeling arbitrary phase aberrations in a resonator and for computing modes, modal losses and frequencies in the aberrated resonator. The method is then used to assess the effect of thermal phase aberrations in lasers where the active medium is a solid state rod, and in lasers where the active medium is an OPS (Optically Pumped semiconductor). The adverse effect of the thermal aberrations is found to be severe in the case of rod geometries and small and less significant in the case of OPS lasers. The analysis conducted allows one to identify simple design criteria that further minimize the effect of thermal aberrations in the case of OPS lasers.

We report a passively mode-locked optically pumped semiconductor disk laser with emission at 1220 nm. Both the gain and the semiconductor saturable absorber mirrors used to build the laser are based on InGaAsN/GaAs quantum wells fabricated by molecular beam epitaxy. The growth parameters have been optimized to reduce the detrimental effects of nitrogen on the emission efficiency. Using a gain mirror comprising ten GaInNAs quantum wells with a relatively low nitrogen content and a saturable absorber mirror incorporating two GaInNAs quantum wells, we demonstrate generation of pulses with durations of ~5ps and average powers up to 275mW. We describe the fabrication procedure of the semiconductor structures and the results of laser characterization.

We report the first use of a Semiconductor Disk Laser (SDL) as a pump source for ~2μm-emitting Tm³⁺ (,Ho³⁺)-doped dielectric lasers. The ~1213nm GaInNAs/GaAs SDL produces >1W of CW output power, a maximum power transfer net slope efficiency of 18.5%, and a full width half maximum wavelength tuning range of ~24nm. Free-running operation of a Tm³⁺-doped tellurite glass laser under 1213nm SDL pumping generated up to 60mW output power with 22.4% slope efficiency. Wavelength tunable output is also obtained from 1845 to 2043nm. Improved performance with output powers of ~200mW and a slope efficiency of ~35% are achieved by replacing the Tm³⁺-doped glass with a Tm³⁺-doped KYW active medium. Emission of a Tm3+,Ho3+-codoped tellurite glass laser is also reported with maximum output power of ~12mW and a ~7% slope efficiency. Finally, preliminary investigations of 1213nm-pumping of a Tm³⁺,Ho³⁺-codoped silica fibre laser lead to 36mW output power with ~19.3% slope efficiency.

A frequency-converted optically pumped semiconductor laser (OPSL) is described. The 976-nm OPSL is frequency doubled intracavity and is forced to operate in single longitudinal mode. An external resonator, containing a cesium lithium borate crystal is locked to the 488-nm fundamental, generating the second harmonic at 244 nm. Continuous wave output in excess of 200 mW is generated.

Optically-pumped semiconductor lasers provide efficient laser sources in the ultraviolet by intra-cavity nonlinear frequency tripling. A laser combining InGaAs gain media with LBO nonlinear crystals produces hundreds of mW CW at 355 nm. A compact package that combines thermal and opto-mechanical stability is the key to making this laser robust and manufacturable. A temperature controlled, monolithic aluminum base supports opto-mechanical mounts made from low expansion alloys and ceramics to create a resonator that can withstand substantial environmental excursions.

Optically pumped semiconductor lasers are scalable up to several 10ths of Watts of output power, maintaining excellent beam quality and high reliability. A further key advantage of the OPS technology is wavelength flexibility: the accessible wavelength range spans from 915 nm to 1180 nm. Frequency doubling expands this into the blue to yellow spectral range. The current investigation aims at applications (such as Raman spectroscopy) where ultra-narrow bandwidth lasers are required. Results of a single frequency green-yellow OPS laser will be presented.

Compact laser light sources in the visible spectral range emitting several Watts are required for display technology, sensor systems and material processing. Second harmonic generation (SHG) using highly brilliant edge emitting infrared lasers is a promising way to fill the spectral gap of directly emitting semiconductor lasers. Newly developed distributed Bragg reflector (DBR) tapered lasers allow a very efficient SHG due to their extraordinary brightness. On an optical bench more than 1 W power at 488 nm was obtained by directly doubling the laser light with a 5 cm long PPLN crystal. Using hybrid integration on a micro-optical benches we now achieved 0.5 W power at 488 nm with a 2.2 cm long PPLN crystal.

Electrically pumped vertical cavity surface emitting lasers (VCSELs) can produce hundreds of mW's of 976 nm CW output in a TEM00 mode when operated with an external cavity configuration. During pulsed operation (<50ns) a significant increase in the peak power is observed, compared to CW operation. High peak powers makes these lasers very well suited for intra-cavity frequency doubling with a non-linear crystal. We are developing surface emitting lasers in 2D array format and high power pulsed blue laser arrays in a small size. We present results of CW and pulsed operation of such lasers.

Recent achievements in second harmonic generation (SHG) from mid-IR diode lasers have made the realization of compact blue-light sources with high power a reality. Moreover, narrow linewidth control of IR sources based on broad stripe high power devices makes it possible to achieve a wide range of wavelengths throughout the blue region. This paper summarizes recent results utilizing a novel Master Oscillator Power Amplifier configuration for blue light generation.

We review recent results concerning the development of GaSb-based heterostructures for semiconductor disk lasers. We focus on fabrication and design details of gain and semiconductor saturable absorber mirrors used to demonstrate disk lasers exhibiting high output power, broad tunability, and short pulse generation. We demonstrate a 2 μm gain structure with 15 InGaSb quantum wells emitting more than 4 W of output power at 15°C. Almost 1W output power was measured at an elevated temperature of 50°C. A tuning range of more than 150 nm was achieved by employing a gain mirror comprising quantum wells with different widths to provide broadband gain. Ultra-short pulse generation based on synchronous mode-locking and a preliminary demonstration of passively mode-locked semiconductor disk lasers based on GaSb saturable absorber mirrors are also discussed.

Optically pumped VECSELs (vertical external cavity surface emitting lasers) with above 5 μm emission wavelength were fabricated on BaF₂ and Si substrates. The active layer is just 1 - 2 μm thick PbTe or PbSe, and epitaxial PbEuTe/BaF₂ or PbSrTe/EuTe Bragg mirrors are employed. On BaF₂ substrates, output powers up to 260 mW pulsed and 3 mW cw at 100 K are obtained. The VECSEL presently operate up to 175 K with PbTe, and up to 215 K with PbSe active layers. On Si-substrates, maximum output was about 30 mW. There is room for considerable improvement with better adapted designs including improved heat-removal precautions.

Cryogenically-cooled diode-pumped lasers have received significant interest in recent years for their demonstrated orders of magnitude improvement in output radiance using simple laser resonator configurations, with respect to their room temperature counterparts. Here we present a technique that offers the potential for a further order-of-magnitude radiance improvement utilising the in-band pumping hybrid-laser architecture, which employs high-power fiber lasers to excite cryogenically-cooled bulk gain media. The ability to exploit the quasi-four-level nature of a two-level laser system at very cold temperatures enables the operation of very low quantum defect transitions, thus providing reduction in the required thermal dissipation per unit power for the in-band pumped Ho:YAG laser, compared to diode-pumped Yb:YAG. Preliminary results will be discussed for a narrow linewidth Tm:fiber laser system operating in the 100W regime, pumping a cryogenically cooled Ho:YAG gain element, and employing a simple cavity configuration. Low quantum defect operation and power-scaling potential will be discussed.

Eye-safe, high power, tunable, narrow linewidth lasers are key technologies for a number of applications, including atmospheric propagation measurements. Since the atmosphere has narrow line transmission windows it is important to have a tunable linewidth source which can be matched to the transmission window. We have developed a stable narrow-linewidth (0.3 nm), tunable (from 1947 nm to 2108 nm) large mode area thulium doped fiber laser. Using this as a seed source, a master oscillator power amplifier with ~100 W output power will be presented.

We demonstrate, for the first time, room-temperature, 10 W (at 2400 nm), Er-fiber laser pumped, pure CW, thermally diffusion doped, polycrystalline Cr²⁺:ZnS laser. We also show Littrow-grating, single-knob, wavelength tuning of the laser over 1940-2780 nm with the maximum output power of 7.4 W at 2400 nm and above 2 W over 1970-2760 nm wavelength range. The laser performs with 40% real optical efficiency (with 43% slope) and shows no output power roll-off up to the highest available pump of 26 W.

Fe:ZnSe is one of the most promising materials capable of generating broadly tunable laser radiation in the wavelength range from 3.5 to 5 μm. The aim of the work was to test laser properties of the Bridgman-method-grown Fe²⁺:ZnSe crystal activated through the synthesis process as an active medium coherently pumped with the Q-switched Er:YAG laser whose oscillation wavelength (2937 nm) corresponds to the maximum of the Fe²⁺:ZnSe absorption spectrum. The Er:YAG laser generated giant pulses with the duration 160 - 200 ns and energy 20 - 30 mJ. The repetition-rate was set to be 1 Hz. The oscillation properties, such as the pulse length, energy, and generated beam spatial structure, of the Bridgman-method-grown Fe2+:ZnSe crystal used as an active medium of Fe²⁺:ZnSe laser operated at room temperature were investigated. The maximal obtained output energy of room temperature Fe²⁺:ZnSe laser was 580 μJ for the absorbed energy of 5.3 mJ which corresponds to slope efficiency of 38%. The generated pulse waveform was found to follow that of the pump one.

We have studied experimentally and numerically the pulse shaping dynamics of a diode-pumped thin-disk laser oscillator with active multipass cell and large output coupling rates. We demonstrate the generation of high energy subpicosecond pulses with energies of up to 25.9 μJ and durations of 928 fs directly from a thin-disk laser oscillator without further amplification. We have achieved these results by employing a selfimaging active multipass geometry in order to increase the output coupling rate for a suppression of nonlinear optical effects. With this system we have obtained stable single pulse operation in ambient atmosphere with average output powers above 76W at a repetition rate of 2.93 MHz. A semiconductor saturable absorber mirror was used to start and stabilize passive soliton mode locking. The experimentally studied laser pulses show good agreement with numerical simulations including the appearance of Kelly sidebands. We present a modification to the soliton area theorem that is applicable for such a laser oscillator with active multiple pass cell and large output coupling rate. While numerically simulating the laser, we also investigated the intracavity pulse dynamics within one round-trip and limitations for power scaling. Furthermore, we demonstrate the laser's potential for micro machining applications by showing first examples of material processing, such as the determination of ablation thresholds and ablation rates for various materials.

Recent development of optically-pumped semiconductor laser (OPSL) technology provide a Ti:sapphire pump source reducing cost and complexity while maintaining a high standard of performance and reliability. In this paper we report on the performance of a compact (930 x 330 x 170 mm³), cavity-dumped ultrafast Ti:Sapphire laser oscillator pumped by an OPSL and using negative dispersion mirrors. The system generates broadband pulses of more than 45nJ pulse energy from single shot to 2 MHz repetition rate. At higher repetition rates the pulse energy decreases as it is typical for cavity dumped laser systems, but with 10 nJ at 27 MHz (division ratio of 1:2) the pulse energy is at the level of the Mantis in standard configuration (8 nJ). FWHM spectrum of the Mantis is specified >70nm and bandwidth over 100nm could be achieved by fine adjustment of the dispersion with intracavity wedges. Compressed pulse duration down to 12.5fs was measured. The system is based on the standard Coherent Mantis laser with a cavity dumper extension, making the footprint only 350 mm longer. It can be user configured either as standard oscillator or as a cavity dumped oscillator.

We present a new Optical Parametric Oscillator (OPO) based on collinear, quasi phase-matched interaction in a periodically poled crystal (PP-crystal) with an integrated extra-cavity prism compressor delivering Signal pulses with durations as low as 30 fs around 1150 nm center wavelength. The design matching between the Ti:Sapphire pump laser (Coherent Micra-10 or MiraV10), the PP-crystal and the intra-cavity dispersion compensation of the OPO enables stable Signal emission covering a spectral region from 1050 nm to 1250 nm with pulse energies exceeding 4.5nJ. Tunability of the Signal pulses between 1130 nm and 1200 nm is given at reduced bandwidth.

Non-interacting Boson-like properties of light beams imply that superposed light beams by themselves cannot re-organize or re-distribute their energies either in spatial or in the time domain. Yet, we explain short pulse generation by lasers with intra-cavity devices as due to phase locking of the longitudinal modes of the laser cavity, irrespective of whether the lasing material has homogeneously or in-homogeneously broadened spectral characteristics. Most short pulse generating "mode locked" lasers use homogeneously broadened gain media that always tend to run in a single frequency at the gain line center that has the highest gain under CW condition. Can a passive intra-cavity saturable absorber or a Kerr medium switch the spectral characteristics of a homogeneously broadened gain medium into an in-homogeneously broadened gain medium to make the laser run in multiple longitudinal modes? We believe that the lasing medium runs in a single mode (frequency) at the center of the gain medium and the intra-cavity saturable absorber or the Kerr medium simply plays the role of fast time gating (switching). This implies that "transform limited" "mode-locked" laser pulses, in reality, contain only a single carrier frequency. We will present the appropriate mathematical representation for the spectral analysis of such "mode-locked" pulses. We will also discuss models for the physical process that give rise to the generation of short (nanosecond class) pulses even in the absence of multiple longitudinal modes and then use the concepts for generating shorter (picosecond and femtosecond) pulses.

The disk laser concept aggregates high efficiency, excellent beam quality, high average and peak power with moderate cost and high reliability. Therefore it became one major technology in industrial laser material processing. In several large scale installations in the automotive industry, high power cw- systems make already use of the high brightness and high efficiency of disk lasers, e.g. in remote welding [1,2]. Other applications including cutting, drilling, deep welding and hybrid welding are arising. This report highlights the latest results in cw disk laser development. A 1.5 kW source with a beam parameter product (BPP) of 2 mm mrad is described as well as the demonstration of a 14 kW system out of three disks with a BPP of 8 mm mrad. The future prospects regarding increased power and even further improved productivity and economics are presented. A new industrial disk laser series with output powers up to 16 kW and a beam parameter product of 8 mm*mrad will enable both, new applications in the thick sheet area and very cost efficient high productive applications like welding and cutting of thin sheets.

A thin disk regenerative amplifier based on Yb:KLW (potassium lutetium tungstate) is operated in different set-ups, changing the net gain and total amount of nonlinearity during amplification. Spectrum broadening during amplification produces Lorentz-shaped pulses with an autocorrelation width of 190 fs after dispersion compenstaion. Damping of bifurcations is demonstrated by nonlinear spectrum broadening, allowing stable operation with an output energy of of nearly 400 μJ at 50 kHz.

The quasi two-dimensional geometry of the disk laser results in conceptional advantages over other geometries. Fundamentally, the thin disk laser allows true power scaling by increasing the pump spot diameter on the disk while keeping the power density constant. This scaling procedure keeps optical peak intensity, temperature, stress profile, and optical path differences in the disk nearly unchanged. The required pump beam brightness - a main cost driver of DPSSL systems - also remains constant. We present these fundamental concepts and present results in the wide range of multi kW-class CW-sources, high power Q-switched sources and ultrashort pulsed sources.

We present an overview of quenching processes in Yb-doped lasers. Experiments made on Yb:YAG crystals and Yb-doped fiber lasers show that induced losses appear upon UV-irradiation through a charge-transfer process. The valence stability of the Yb ion is believed to be the key issue for the quenching processes in Yb-doped high power laser systems.

A significant reduction of the influence of the thermal lens in thin-disk lasers in high power laser operation mode could be achieved, using dynamically stable resonators. For designing the resonator, investigations of thermally induced phase distortions of thin-disks as well as numerical simulations of the field distribution in the resonator were performed. This characterization was combined with thermo-mechanical computations. On the basis of these studies, about 500 W output power with an averaged M² = 1.55 could be demonstrated, using one disk. Almost 1 kW output power with good beam quality could be extracted, using two disks. For the purpose of further power scaling in nearly fundamental mode operation, experiments using more than two disks are in preparation.

Polycrystalline ceramic laser materials are gaining importance in the development of novel diode-pumped solid-state lasers. Compared to single-crystals, ceramic laser materials offer advantages in terms of ease of fabrication, shape, size, and control of dopant concentrations. Recently, we have developed Neodymium doped Yttria (Nd:Y₂O₃) as a solid-state ceramic laser material. A scalable production method was utilized to make spherical non agglomerated and monodisperse metastable ceramic powders of compositions that were used to fabricate polycrystalline ceramic material components. This processing technique allowed for higher doping concentrations without the segregation problems that are normally encountered in single crystalline growth. We have successfully fabricated undoped and Neodymium doped Yttria material up to 2" in diameter, Ytterbium doped Yttria, and erbium doped Yttria. We are also in the process of developing other sesquioxides such as scandium Oxide (Sc₂O₃) and Lutesium Oxide (Lu₂O₃) doped with Ytterbium, erbium and thulium dopants. In this paper, we present our initial results on the material, optical, and spectroscopic properties of the doped and undoped sesquioxide materials. Polycrystalline ceramic lasers have enormous potential applications including remote sensing, chem.-bio detection, and space exploration research. It is also potentially much less expensive to produce ceramic laser materials compared to their single crystalline counterparts because of the shorter fabrication time and the potential for mass production in large sizes.

For future satellite based water vapour DIAL systems, efficient and rugged laser sources are required preferably around 935 nm. The quasi 4-level transition from R₂ to Z₅ in Nd:YGG is a promising candidate for its direct generation. Q-switch operation at 100 Hz with pulse energies up to 7.7 mJ is reported as well as single frequency operation with an injection seeded system stabilized by ramp-and-fire-method. The pulse energy of a 4.5 mJ oscillator was scaled to 32 mJ with an InnoSlab-based amplifier at nearly diffraction limited beam quality of M² < 1.4. Heterodyne measurements show a line width of less than 28 MHz.

We report on efficient operation of highly doped 2.4 at. % crystalline Czochralski grown Nd:YAG at 1.06μm, 1.3μm and 1.4μm in a diode pumped bounce amplifier configuration under quasi-continuous pumping. At wavelength of 1064nm the linearly polarized pulses with energy of 16.8 mJ in free running regime with repetition rate of 10 Hz (optical to optical efficiency of 44.6 % and slope efficiency of 50%) and 1 mJ in passively Q-switched regime with pulse duration of 6.4 ns were generated.The passively Q switched operation at 1.3μm was also demonstrated.

To reduce the cost of energy obtained from photovoltaic cells, advanced cell design and processes are required for solar cell manufacturing. Many of these designs and processes are enabled by laser processing. As the availability of higher power and high beam quality pulsed solid state lasers increases, lasers are expected to find increased application in solar cell manufacturing. Solar cell processing will benefit further as production worthy lasers with picosecond pulse width become available. Picosecond lasers are well suited for selective removal of dielectrics for front and back metallization applications due to reduced thermal effect on the underlying substrate. We present results on silicon nitride and silicon oxide ablation that may find applications in advanced cell architecture.

Demand for higher precision, clean laser based processes has driven the development of picosecond pulse width lasers that operate at high frequency with high average powers. Industries like microelectronics and LCD manufacturing are gearing up for the next generation of devices that demand tighter densities, better electrical efficiency, higher speed and better quality. We focus here on the differences between processing with nanosecond and picosecond pulses on Silicon and on alumino-borosilicate glass.

In this paper we presented a pulse shaping technique on regular solid-state lasers and the application in semiconductor micromachining. With a conventional Q-switched laser, all of the parameters can be adjusted over only limited ranges, especially the pulse width and pulse shape. However, some laser link processes using traditional laser pulses with pulse widths of a few nanoseconds to a few tens of nanoseconds tend to over-crater in thicker overlying passivation layers and thereby cause IC reliability problems. Use of a laser pulse with a special shape and a fast leading edge, such as tailored pulse, is one technique for controlling link processing. The pulse shaping technique is based on light-loop controlled optical modulation to shape conventional Q-switched solid-state lasers. One advantage of the pulse shaping technique is to provide a tailored pulse shape that can be programmed to have more than one amplitude value. Moreover, it has the capability of providing programmable tailored pulse shapes with discrete amplitude and time duration components. In addition, it provides fast rising and fall time of each pulse at fairly high repetition rate at 355nm with good beam quality. The regular-to-shaped efficiency is up to 50%. We conclude with a discussion of current results for laser processing of semiconductor memory link structures using programmable temporal pulse shapes. The processing experiments showed promising results with shaped pulse.

The combination of high spatial coherence, wide tunability and broad intrinsic bandwidth makes femtosecond optical parametric oscillators (OPOs) uniquely attractive sources for spectroscopy in the visible and infrared. In the mid-infrared the idler pulse bandwidths from such systems can extend over several hundred nanometres, making Fourier-transform spectroscopy possible, and transferring the wavelength calibration and resolution constraints from the OPO to the detection system. Unlike thermal sources of mid-infrared radiation, the spatial coherence of the output from femtosecond OPOs is extremely high, with the potential for spectroscopic measurements to be made over long free-space path lengths, in fiber or at the focus of a microscope objective. Using OPOs based on MgO:PPLN, and pumped by a self-modelocked Ti:sapphire laser, we have shown free-space and photonic-crystal-fiber-based spectroscopy of methane to concentrations as low as 50 ppm. The spectral bandwidth of the idler pulses used for gas sensing exceeds 200 nm, allowing the principal methane absorption lines around 3.3 μm to be acquired without wavelength tuning the OPO. Practical Ti:sapphire and Yb:fiber pumped based OPOs have been demonstrated that offer combinations of flexible tuning, high stability, low-threshold operation and high-energy output pulses.

We describe a modular ultrafast spectroscopy setup based on standard commercially available components that can easily be configured to conduct multi-beam and multi-color multimodal pump-probe ultrafast experiments. Multimodality of the setup is demonstrated on examples of transient absorption and different types of four-wave mixing time resolved experiments in colloidal nanoparticles, neat liquids and solutions.

We report a system for optical trapping, manipulation and imaging of live cells in close to real-time with a wide field of view. A fs-pulsed Ti:Sapphire source was used to trap cells whilst an Ar⁺ laser was used for confocal imaging. A single 10x/0.4NA lens and a dual scanning system enabled independent trapping, imaging and movement of cells over a field of view >1mm². We will present movies of controlled T cell and dendritic cell movement and interaction. This enables the functional study of cell-signalling processes that are fundamental to understanding the behaviour of the immune system and beyond.

We discuss the requirements for laser systems used in Coherent Anti-Stokes Raman Scattering (CARS) microscopy and particularly in its wide-field modification. While such laser parameters as wavelength, spectral width and frequency difference between pump and Stokes beams are similar for all CARS systems, requirements for pulse energy, repetition rate, pulse length and mode structure might be significantly different for scanning and wide-field approaches. We will present results obtained with a wide-field CARS microscope with non-phase matching illumination and compare its performance with other CARS microscopes. Objectives for the design of future laser systems for CARS microscopy will be outlined.

Within the vast range of laser materials processing applications, every type of successful commercial laser has been driven by a major industrial process. For high average power, high peak power, nanosecond pulse duration Nd:YAG DPSS lasers, the enabling process is high speed surface engineering. This includes applications such as thin film patterning and selective coating removal in markets such as the flat panel displays (FPD), solar and automotive industries. Applications such as these tend to require working spots that have uniform intensity distribution using specific shapes and dimensions, so a range of innovative beam delivery systems have been developed that convert the gaussian beam shape produced by the laser into a range of rectangular and/or shaped spots, as required by demands of each project. In this paper the authors will discuss the key parameters of this type of laser and examine why they are important for high speed surface engineering projects, and how they affect the underlying laser-material interaction and the removal mechanism. Several case studies will be considered in the FPD and solar markets, exploring the close link between the application, the key laser characteristics and the beam delivery system that link these together.

Through an optimal combination of crystal shape, cooling and resonator design, INNOSLAB lasers possess special features: short pulse duration and high peak output power, high pulse repetition rate, high beam quality at high average power and flexibility in beam profile, from circular beam profile, through line shaped one dimensional top-hat, to two dimensional top-hat with rectangular cross section. Those open for INNOSLAB laser a variety of unique applications with added value, such glass processing, scribing, and particle imaging velocimetry and pumping of dye lasers.

A multi petawatt high energy power chain is under construction at CEA-CESTA for the PETAL (PETawatt Aquitaine Laser) project within the LIL facility. It requires an Nd: glass high energy Amplifier, with sixteen 757 mm x 402 mm aperture laser slabs to increase the injected chirped pulse (44 mJ) up to 6.4 kJ. To take account of the PETAL project requirements, optical, electrical, mechanical and cooling optimizations have been performed to design this amplifier system, divided into two parts sized approximately 1.2 m x 1.2 m x 8m. The solutions adopted made it possible to control the laser gain over the full aperture, to obtain a 15 μrad mechanical stability for each laser slab with predicted vibratory PSD and approximately a 1 hour period for laser cooling.

It was shown that broadband near infrared fluorescence in recently discovered in Bi-doped glasses is not specific to Biions. Germanate glasses doped with different 6p (Bi, Pb) and 5p (Sn, Sb) ions (co-doped with Al) exhibit similar behavior. The centers can be characterized by 4 peaks in the excitation-emission plots. The decay of fluorescence (excited with short laser pulse at 800 nm and 532 nm) has complex behavior. The components of the decay are in the nsto ms- range and they have different temperature dependences. To our opinion, existing models of optical center suggested earlier should be revised to agree with new data.

A CW operating, high-power, high-efficient diode pumped 2μm laser was based on Tm:YAP (Tm³⁺ doped YAlO₃) active medium. To enhance the output beam quality, laser stability, and compactness, a microchip configuration was used. In this arrangement the resonator mirrors were deposited directly on to the laser crystal faces. Two groups of laser crystals were tested - with doping 3 or 4 at.% of Tm/Y. In each group, laser resonators without and with pumping radiation recuperation were investigated. The first one used 3mm long active medium and output coupler was transparent for pumping radiation. The second one used only 2mm long active medium but the pumping radiation, unabsorbed after first pass, was reflected back by the output coupler. For the generated laser radiation the output coupler reflectivity was 97 %. The diameter of all samples was 3mm and the a-cut (Pbnm) of Tm:YAP was used. For the laser pumping, a fibre coupled laser diode operating at wavelength 0.79 μm was used. The 400 μm fiber was delivering up to 25W of pump power to the coupling optics. All crystals were studied under the same pumping and cooling conditions and results were compared. The best results were obtained for 2mm long Tm:YAP crystal (3mm diameter, 4 at.% Tm³⁺). The output power 6.2W @ 1994nm in linearly polarized close to TEM₀₀ beam was obtained for incident pumping power 20.2W @ 793 nm. The differential efficiency in respect to the incident pump power reached 34% while the maximal attained optical-tooptical efficiency was ~ 31 %.

Disordered crystals combining the advantages of both crystals and glasses are very interesting for applications in tunable, Q-switched, and mode-locked solid-state lasers. Calcium niobium gallium garnet, Ca₃(NbGa)_2-xGa₃O₁₂ (CNGG), has a thermal conductivity of 4.7 Wm^-1K^-1 which is about 40% of that of undoped YAG and much higher than for glasses. It has a number of non-equivalent lattice sites to accommodate trivalent dopant ions, providing an effective mechanism for substantial inhomogeneous line broadening. For the Yb ion, owing to its intrinsic broad absorption and emission spectra, this line broadening effect is not so remarkable as for Nd or Tm but still the main emission band around 1028 nm of Yb:CNGG, with a FWHM of 21 nm is two times wider than the corresponding line (<10 nm) in Yb:YAG. Here, we report efficient laser operation achieved with Yb:CNGG at room temperature in cw as well as Q-switched regimes, revealing interesting characteristics of the laser oscillation. 2.0 W of cw output power were produced at an absorbed pump power of 6.32 W, leading to an optical-to-optical efficiency of 32% and a slope efficiency of 40%. The laser oscillation of the isotropic crystal was actually linearly polarized as a result of the stress-induced birefringence. Two orthogonal polarization states oscillated simultaneously at high pump power levels. Passive Q-switching by a Cr⁴⁺:YAG saturable absorber produced 1.35 W of average output power at 1033 nm at a pulse repetition rate of 16.7 kHz. The laser pulse energy, duration, and peak power were 81 μJ, 25 ns, and 3.24 kW, respectively.

GdCa₄O(BO₃)₃ (GdCOB) is a promising host material for the trivalent Yb-ion with large splitting (>1000 cm^-1) of the ground state (²F_7/2) which facilitates efficient laser operation at room temperature. There have been a number of investigations in the continuous-wave (cw) regime, however, most of the previous studies ignored the issue of crystal orientation. GdCOB is a low symmetry biaxial crystal (point group m) and the absorption and emission spectra of Yb exhibit strong anisotropy. Here we report our experimental results with Yb:GdCOB crystals cut along the three principal optical axes under high-power unpolarized diode pumping in a simple plano-concave cavity. Our study reveals clearly significant anisotropy of the laser performance of Yb:GdCOB. For the y-cut crystal, polarized laser oscillation along the x- or z-axes is feasible, depending on the output coupling (T) utilized; with a specific T = 3% the two orthogonal polarization states exist simultaneously at different emission wavelengths. The laser oscillation obtained with the x- and z-cut crystals is polarized along the z- and x-axes, respectively, independent of T and the power level. Despite its complex output-coupling-dependent nature of laser oscillation, the y-cut crystal turns out to be the most promising for efficient high-power operation. A cw output power of 7.35 W at 1083-1085 nm polarized along the x-axis is obtained at room temperature, with an optical-to-optical efficiency of 63% and slope efficiency as high as 84%.

We developed a compact Yb:YAG ceramic regenerative amplification system. A rectangular glass block is used to elongate the cavity. A pulse to be amplified is propagated in a long distance in the glass block by being reflected repetitively at the end faces of the glass under a condition of total internal reflection. Furthermore, we produced transmission gratings with a diffraction efficiency of more than 95%. The floor area of the entire amplification system is reduced to less than 2,000 cm². In 20-kHz operation, the system generates 1.0-ps compressed pulses of 4.5-W average power, i.e., 0.225-mJ energy.

Successful room-temperature generation of Pr:YAP laser radiation at wavelengths of 747 nm and 662 nm was demonstrated. A flash-lamp pumped Pr:YAP laser was operated in free-running pulsed regime at room temperature. Permanent laser action was reached by means of a special UV color glass plate filter placed directly into the laser cavity. The maximum output energy and pulse length reached at wavelengths of 747 nm and 662 nm were 102 mJ, 92 μs and 6.1 mJ, 47.5 μs, respectively. The laser beam parameter M2 ~ 1.5 was measured when the 662 nm wavelength was generated. In the case of 747 nm wavelength generation, M2 ~ 1.2 was reached with a diaphragm inside the resonator. For different pumped energy values, the line shape and linewidth remained stable for both cases.

An analytical model of a CW pumped passively Q-switched microchip laser in plane wave approximation is presented. The dynamics of such laser can be described by set of rate equation. Our model is based on possibility to express the analytical solution of simplified rate equations with the help of LambertW function. The LambertW function is now commonly available in most of mathematical software and became to be easy to use. Next, the significant simplification of saturable absorber dynamics is made and its presence is described only by its initial and saturated transmission. The analytical form of solution allows to study quickly and transparently the behavior of the laser with a sufficient accuracy. Using this model it is possible to estimate giant pulse parameters, like pulse length and energy density, the pulse repetition rate, and the laser input-output power characteristic. The validity limits of this model were verified using numerical solution of more complicated rate equations model which included nonlinear response of the modulator. The model was also compared with experimental results obtained for passively Q-switched diode pumped Nd:YAG/V:YAG microchip laser operating at 1338nm and good agreement was obtained. Although the described model was designed primary for such kind of compact short cavity laser, the results are useful for any other passively or actively Q-switched laser with a fast-operating modulator.

Resonant pumping by a solid state Er:glass laser was successfully examined for Er:YAG and for the first time also for Er:YAP laser. The maximal incident pumping energy on the wavelength 1535 nm was 640 mJ with a repetition rate of 0.5 Hz; the corresponding pulse length was 1.9 ms (FWHM). The Er:glass laser radiation was focused into the active crystal by a CaF₂ lens with 70 mm focal length. The measured beam diameter in focal plane was ~ 400 μm. The Er:YAG and Er:YAP rods had 10 mm in length and 5 mm in diameter. Various concentrations of Er³⁺ ions were used: 0.5 at.% for YAG and 1 at.% for YAP crystal. The resonator consisted of pumping and output dielectric mirrors. For both cases, the pumping dielectric mirror with high transmittance at pumping wavelength (T > 95 % @ 1532 nm) and maximal reflectance at the oscillating wavelength (around 1640 nm) was used. The output coupler reflectance was 85 % and 90 % for 1532 nm and 1640 nm, respectively. The advantage of resonantly pumped lasers is low thermal load corresponding to low quantum defect, and, therefore, it was not necessary to cool the active crystals. The output generated energy for the Er:YAG laser medium was 45 mJ at 1648 nm for 465 mJ incident pumping energy. For Er:YAP crystal the energy reached was 20 mJ at the lasing wavelength 1623 nm. The incident pumping was 640 mJ. For both resonantly pumped laser systems other characteristics i.e., spatial beam structure, divergence, and efficiency were investigated.

A novel fiber-based Q-switched master-oscillator & power-amplifier system was developed by using non-PM Yb fiber with side pumping by single source. The passive Q-switched system provides for pulse energy up to 110 microjoule at CW 12 W single pump. Duration and repetition rate of generated pulses at 1080 nm can be varied from 280 ns to 1,8 microsecond, and in the range of 45-140 kHz depending on pump power at 980 nm. Design of master oscillator ensures linearly polarized output which remains polarized after passing power amplifier. Maximum stable average output of the system was 5 W and above this value we observed appearance of nonregular giant pulses which were able to initiate supercontinuum generation over 550-1750 nm range in relatively short-length microstructured fibre. For the first time to our knowledge, wideband supercontinuum generation was obtained with microsecond laser system pump. More details and results including applications for materials processing will be presented.

We report methods of fabrication and laser-spectroscopic characterization of mid-IR gain media based on micron size Cr²⁺:ZnSe/ZnS powders, as well as Cr²⁺:ZnSe/ZnS doped fluorocarbon polymer films, and perfluorocarbon liquids. All samples demonstrated strong mid-IR luminescence over 2000-3000nm spectral range under optical 1700nm excitation. The random lasing of the doped liquids and polymer films was realized with pump energy density of 100 and 15mJ/cm2, respectively. Previously we have demonstrated mid-IR electroluminescence of Cr:ZnSe with n-conductivity provided by thermal diffusion of Al and Zn. However, the formation of conductivity was accompanied by compensation of the Cr²⁺ optical centers and relatively weak chromium electroluminescence. In this paper we report study of the Cr²⁺ compensation in the crystals co-doped with donor and acceptor impurities. Optical and electrical characterization of Cr:ZnSe crystals with Ag, Cu, Al, In, and Zn co-dopants were studied to optimize mid-IR electroluminescens of the Cr²⁺ ions. The best results were obtained with p-conductive Ag:Cr:ZnSe samples featuring a low 600 Ωcm resistivity. First mid-IR electroluminescence in presumable p-type Ag:Cr:ZnSe was demonstrated, which could prove valuable for developing laser diodes that function in this spectral region.

We present developed computer-controlled tuneable laser system based on CW narrow-line Ti:Sapphire/Dye laser which is meant for laser-optical characterisation of quantum dot properties. The full set of laser system options allows it to cover a spectral range from 275 to 1100 nm while having the output line width around 0.5-1 GHz. The system includes a built-in high-precision radiation wavelength meter and a system of automatic control over the spectrally selective laser elements, thus providing the possibility to automatically set the output radiation wavelength to the absolute precision of 1 GHz (0.004 meV) and to perform continuous scanning of the output radiation line in a specified spectral range.