This PDF file contains the front matter associated with SPIE Proceedings Volume 6871, including the Title Page, Copyright information, Table of Contents, Plenary Paper and the Conference Committee listing.

We present a Q-switched microchip laser emitting 1064nm pulses as short as 100ps synchronized to a cavity dumped femtosecond laser emitting 800nm pulses as short as 80fs. The synchronization is achieved by presaturating the saturable absorber of the microchip laser with femtosecond pulses even though both lasers emit at different wavelengths. The mean timing jitter is 40ps and thus considerably shorter than the pulse duration of the microchip laser.

A new instrument design allows the M² beam propagation ratio to be measured in real time at the update rate of a standard CCD camera. This allows lasers from single shot to CW to be measured while the laser cavities are being adjusted. This drastically reduces the test time required for this operation. In this paper we will discuss the theory behind this innovative approach to the M² measurement and the methods for the selection of the proper optical components for use of the system with various laser types and beam shapes. The authors will show results of numerous measurements of different lasers and laser types, including solid state diode and traditional gas lasers with M² values from near 1 to considerably higher values, and show comparisons these results with other measurement methods. The instrument design is based on a method of simultaneous capture of the waist and several Rayleigh ranges, allowing the instantaneous fit of the ISO M² propagation curve. The authors will discuss the important considerations necessary to generate accurate results for different laser configurations.

This paper discusses an novel strategy in development, design and integration of a high efficient Q-switched laser operating on weak transitions of the lasing media. A typical example of such operation is lasing on the 946 nm transition of Nd-doped medium. The proposed approach enables very effective Q-switched operation on this type of weak transitions with the plug-in efficiency better than 10% at a few ns pulse length, as compared to recently reported less than 1% efficiency at pulse length of about 150 ns.

We describe the design and performance of a high-repetition-rate single-frequency passively Q-switched Yb:YAG microlaser operating near 1030 nm. By using short cavity length, an intracavity Brewster polarizer, and an etalon output coupler, we are able to produce ~1-ns-long single-frequency pulses at repetition rates up to 19 kHz without shot-to-shot mode hopping. The laser's output spatial mode is TEM₀₀ and its pulse energy varies between 31 μJ and 47 μJ depending on repetition rate. Its peak optical-to-optical efficiency is 22%.

The optimization of output power and beam quality of a diode pumped solid state laser is a difficult task. In this paper, we present a method to calculate approximate values of the beam quality factor M² and the output power of a laser. Our method is based on the well-known Gauss mode analysis combined with rate equations. As an application we analyze the beam quality of a Q-switched solid state laser.

This paper discusses a novel approach in a seeded Q-switched laser capable in oscillating with no mutual adjustment between cavity resonances and seed emission frequency. The oscillation pulse of such a laser is easy to time-synchronize to external processes. Oscillation of an injection seeded Q-switched Nd:YAG laser module is demonstrated that can laser the pulses from several nsec to about 20 nsec long with the energy level higher than 100 mJ from the slave oscillator and in excess of 200 mJ after a single stage amplification.

The conventional technique for matching and stabilizing the cavity length of seeded Q-switched Nd:YAG lasers is to minimize the pulse build-up time in a lock-in scheme. A disadvantage of this technique is that in order to obtain a robust feedback signal the opening speed of the Q-switch needs to be reduced, which causes timing issues, loss of power, and lengthening the generated pulse. Here an alternative method is presented which mediates these problems. A feedback signal is obtained using microwave frequency range detection of the beating between the longitudinal cavity modes. This novel technique can be implemented with only a minimal modification of the cavity optics and electronics of conventional free-running Nd:YAG lasers.

For spaceborne lidar like the atmospheric backscatter lidar (e.g. ATLID on the ESA EarthCARE mission) highly reliable and efficient laser sources are needed. As pre-development model we realized a Nd:YAG MOPA diode pumped at 100 Hz. With more than 21 % optical-optical efficiency the amplifier based on the InnoSlab design raises the 8 mJ pulse energy from the single frequency rod oscillator to more than 70 mJ. Frequency-tripling leads to more than 25 mJ at 355 nm and a beam quality of M² < 1.7. The total optical-optical efficiency of more than 7.5 % exceeds the efficiency of comparable current lidar transmitter systems at least by a factor of 2. The laser is designed to cope with diode degradation or failure. Moderate pulse intensities in the InnoSlab amplifier offer excellent possibilities to scale the pulse energy to several 100 mJ in a most reliable and efficient way.

We present the final configuration of the space flight laser transmitter as delivered to the LOLA instrument. The laser consists of two oscillators with co-aligned outputs on a single bench, each capable of providing one billion plus shots.

The use of lidars in ground, airborne, and space-based missions can provide earth and planetary science measurements that were previously unavailable. Our approach to the laser transmitters needed for such systems focuses on developing environmentally hardened prototypes whose designs can be validated in fielded ground and airborne remote sensing systems before being used in space-based missions. We are applying this approach to the development of the injection seeded single frequency lasers that will be needed for a number of the next generation of airborne and space-based lidar systems. In this paper we describe our most current version of a single frequency Nd:YAG laser that is designed for use in an unpressurized, high altitude aircraft. It is capable of providing two 20 W 1064 nm output beams at 200 Hz. Temperature controlled ovens that hold the nonlinear crystals needed for frequency doubling and tripling are included in the output path of one of the beams.

We have developed the advanced technology for the frequency stabilization of a nanosecond deep-ultraviolet coherent light source toward manipulating semiconductor atoms by injection locking with a single-frequency Ti:sapphire laser. In order to stabilize injection seeding, we utilized the small change of the build-up time of the slave-laser pulse. The injection-locked laser can acquire significant performances of both narrow linewidth and high peak power. As a result, the fluctuation of the wavelength decreases from 2.1 GHz to 10 MHz due to the injection seeding. The laser performance indicates various potentials useful for manipulating semiconductor atoms.

Within the context of ESA's Living Planet Programme, the European Space Agency has selected three missions embarking lidar instruments: ADM-Aeolus (Atmospheric Dynamics Mission) planed for launch in 2009 with a Doppler Wind Lidar, ALADIN, as unique payload; EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer) planed for launch in 2013 including an ATmospheric backscatter LIDar (ATLID); at last, A-SCOPE (Advanced Space Carbon and Climate Observation of Planet Earth), candidate for the 7^th Earth Explorer, relying on a CO₂ Total Column Differential Absorption Lidar. To mitigate the technical risks for selected missions associated with the different sorts of lidar, ESA has undertaken critical technology developments, from the transmitter to the receiver and covering both components and sub-systems development and characterization. The purpose of this paper is to present the latest results obtained in the area of laser technology that are currently ongoing in support to EarthCARE, A-SCOPE and ADM-Aeolus.

Advanced pulsed thin disk laser sources based on several pulse generation schemes, including regenerative amplification as well as cavity-dumping, will be presented. These sources are able to produce pulse energies in the multi-millijoule range at repetition rates of up to several 100 kHz, resulting in average output powers in excess of 100 W. Also the efficient intra-cavity frequency conversion of these sources will be discussed.

Laser welding has become one of the fastest growing areas for industrial laser applications. The increasing cost effectiveness of the laser process is enabled by the development of new highly efficient laser sources, such as the Disk laser, coupled with decreasing cost per Watt. TRUMPF introduced the Disk laser several years ago, and today it has become the most reliable laser tool on the market. The excellent beam quality and output powers of up to 10 kW enable its application in the automotive industry as well as in the range of thick plate welding, such as heavy construction and ship building. This serves as an overview of the most recent developments on the TRUMPF Disk laser and its industrial applications like cutting, welding, remote welding and hybrid welding, too. The future prospects regarding increased power and even further improved productivity and economics are presented.

In the past decade, the Thin Disk laser design was very successful as a high power laser design for cw lasers with good beam quality and high efficiency. Several numerical models show that the actually demonstrated output powers are far below the scaling limits due to amplified spontaneous emission (ASE). Also pulsed lasers based on Thin Disk amplifiers achieved comparable high average power, but only with medium pulse energies (about 100 mJ). Numerical models show that ASE effects limit the possible pulse energy to values of a few Joule, using the typical high power cw Thin Disk laser design. To evaluate designs for higher pulse energies a time resolved numerical model of pump absorption and ASE was developed and combined with a model of pulse amplification. The evaluation is focused on quasi-cw pumped pulse amplifiers. It includes the analysis of temperature, stress, deformation and thermal lensing, using finite element methods. This numerical model is used to develop thin disk designs for high output energies.

We report on a novel resonantly-pumped, erbium (Er)-based, gas-cooled disk laser (GCDL) scalable to highaverage power (HAP). The GCDL uses edge-pumped composite laser disks known for their near perfect pump uniformity and compact configuration. Edge pumping enables a long path for pump absorption, which permits using low Er concentration and limits upconversion losses. Resonant operation reduces the waste heat load and enables the use of gas rather than liquid for disk cooling. These attributes make it possible to engineer a lightweight and compact laser device operating at eye-safer wavelengths. This paper presents a GCDL concept design and evaluates its performance for several host materials and operating conditions.

This paper highlights unique advantages of the disk laser technology for converting the moderate brilliance of laser diodes into excellent solid state laser beam quality with high efficiency. In contrast to traditional diode pumped solid state lasers, particularly all relevant fluencies remain constant when the power is scaled by increasing the active area of the disk. The state of the art TRUMPF disk laser family is presented, including latest results. Theoretical and practical limits are discussed and an outlook over new disk laser generations including high power cw, q-switched, and amplified systems is given.

In principle, the thin-disk laser concept opens the possibility to demonstrate high power, high efficiency and good beam quality, simultaneously. For this purpose, a very homogeneous pump power distribution on the disk is necessary as well as very low phase distortions of the disk itself. Spatial mode structure and thermal lens effects in an Yb:YAG thin-disk laser have been investigated as function of the pump power in linear and folded resonators. Whereas thermal lens is shown to be very weak due to the thin disk geometry, a strong correlation of the laser mode with respect to the power density distribution of the pump radiation is exhibited. The experimental results are compared with numerical simulations of the field distribution within the resonator as well as in the far field demonstrating the excellent homogeneity of the disk as laser active medium.

Rotary disk laser technology enables high-power nonlinear optics and laser machining. Due to the wavelength dependence of laser-material interaction, the ability to scale laser power across the spectrum is always in great demand in laser processing of materials. Rotary disk laser technology has enabled high-power nonlinear optics by being able to produce in excess of 200 W in single-mode Q-switched laser power at 1 micron. This breakthrough has led to the power scaling of single-mode visible lasers at 515 nm to 88 W and single-mode UV lasers at 343 nm to 53 W which have set power performance record at their respective wavelengths. In this paper, we will present the results of the rotary disk laser sources in the UV, the visible and the infrared. We will also present record-breaking results in dicing and scribing of silicon, single crystal sapphire and PCBs, and in hole drilling of stainless steel.

Resulting from the optimal combination of slab shaped laser crystal, line shaped diode laser beam, large area and one dimensional conduction cooling and hybrid-resonator design, slab lasers unify features: high beam quality, short pulse duration, high pulse energy and high peak power, high pulse repetition rate and average power and scalability at superior performances. In this paper, concepts, features and developments of slab laser oscillators and amplifiers will be presented and discussed.

Neodymium-doped Yttrium Lithium Fluoride (YLF) lasers have traditionally been power-limited by the relatively low tensile strength of the crystal. When power-scaling solid-state lasers, the choice of the gain media geometry, the doping level, and the pumping scheme is dictated by minimizing the impact of thermally induced stress. To date the slab architecture has been the most successful for scaling the average-power of Nd:YLF lasers due to its favorable thermal management. However, for efficient high-radiance laser action it is also necessary to have a good overlap between the cavity mode and the planar gain volume. We present the performance characteristics for an end-pumped slab-laser utilizing a stable low-loss resonator configuration that transforms a circular cavity mode at the output coupler into a very high aspect ratio elliptical beam in the slab gain element to match the pumped volume. The optical arrangement for transforming the beam shape is also suitable for a double-pass slab amplifier configuration. A polarized CW output power of 50W, on the weaker Nd:YLF 1053nm transition was obtained with a single slab gain element and 110W of incident pump power from three spatially multiplexed diode bars. Laser threshold was around 7W and the slope efficiency, with respect to incident power, 46%.

A waveguide with 150 μm core height of 2% Yb:YAG between sapphire claddings is core-pumped at 480W by diode bars coupled into the 13 mm long edge-facet. The pump unit has custom correction of collimation errors and lens aberrations. Using a 6mm width and 7° edge-facet angle, power is limited by competing ASE loss or parasitic oscillation along TIR-trapped internal paths, giving 40 W output for stable and 25 W for unstable resonators. Ray-tracing shows a 20° facet angle is necessary to successfully out-couple ASE from the core. Preliminary operation at 90W and an increased threshold for the parasitic oscillation are obtained.

Several remote sensing applications require pulsed sources in the mid-infrared spectral regime with high average powers and good beam quality. Ho:YAG lasers have a number of attractive features for high power generation at 2.1microns, either for direct applications or as a pump source for parametric conversion to longer infra-red wavelengths. Unfortunately, direct diode pumping of Ho:YAG is not practical, so a two-step process is generally employed in which one or more diode-pumped thulium-doped lasers are used to directly pump (in-band) the Ho:YAG laser. In response, we have investigated a slab-based architecture for scaling the output power of a Tm:YLF laser to the 100W power regime at 1.91microns, corresponding to a strong Ho:YAG absorption line. Multiple slab lasers with moderate beam quality in the plane of the slab can be combined to efficiently end-pump a low-doping concentration Ho:YAG rod in a pump-guided configuration. In a preliminary demonstration, two 2at.% doped Tm:YLF slab lasers with a spatially multiplexed output of 74W were employed to end-pump a 1.5mm diameter, 80mm long, 0.25at.% Ho:YAG barrel-polished rod. A two-mirror plano-concave cavity, with 11% output coupling transmission, produced a CW output of 38W with a slope efficiency of 60% with respect to the incident power. Q-switched operation at a repetition rate of 20Hz with two intra-cavity Brewster plate polarizers and a 60% transmitting output coupler produced 14mJ pulses with a pulse duration (FWHM) of 18ns. This architecture offers an attractive route for future high-power 2micron lasers.

The operation of pulsed diode pumped Nd:GdVO₄ and Nd:YVO₄ slab lasers in a bounce geometry in a free running and a passively mode-locked regime using a semiconductor saturable absorber was demonstrated. Higher efficiency of Nd:GdVO₄ in both regimes was achieved. In the free running regime the optical to optical efficiency of 28.3% was obtained with Nd:YVO₄ and 39.3% with Nd:GdVO₄ crystal in spatial mode close to TEM₀₀. In the passively mode locked regime the Q-switched and mode locked single trains containing 5 pulses were generated for a pump energy of 11 mJ from Nd:YVO₄ while the pump energy for Nd:GdVO₄ was only 5.5 mJ. The pulse duration was 48 ps and 65 ps respectively. Our results clearly demonstrate the advantage of using Nd:GdVO₄ in a pulsed free running and also a passively mode locked diode pumped regime in a bounce geometry.

We summarize the performance of mode-filtered, Yb-doped fiber amplifiers seeded by microchip lasers with nanosecond-duration pulses. These systems offer the advantages of compactness, efficiency, high peak power, diffraction-limited beam quality, and widely variable pulse energy and repetition rate. We review the fundamental limits on pulsed fiber amplifiers imposed by nonlinear processes, with a focus on the specific regime of nanosecond pulses. Different design options for the fiber and the seed laser are discussed, including the effects of pulse duration, wavelength, and linewidth. We show an example of a microchip-seeded, single-stage, single-pass fiber amplifier that produced pulses with 1.1 MW peak power, 0.76 mJ pulse energy, smooth temporal and spectral profiles, diffractionlimited beam quality, and linear polarization.

We report on a hybrid fiber MOPA + solid-state amplifier for frequency conversion and compare a hybrid scheme versus all- fiber MOPA. Using a thoroughly designed master oscillator and optimized fiber amplifiers we were able to achieve 15-30ns long pulses at average powers above 20 W with a good spectral quality and suppressed SBS. Bulk Vanadate amplifiers boosted the 1064nm output power to greater 65W at pulse repetition rates of 300-500 kHz. More than 35 W in green and 20 W of UV light has been obtained at pulse repetition rates above 300 kHz and pulse energies of 30-100 μJ.

Using a hybrid fiber-bulk laser scheme based on Er:YAG, we have achieved ~60 W and ~30 W of continuous-wave output at 1645nm and 1617nm respectively, and Q-switched pulse energies up to ~30 mJ (limited by coating damage). Investigation of various factors influencing laser performance has revealed that energy-transfer-upconversion can have a very detrimental impact on efficiency, even in continuous-wave mode of operation. In this paper we report on the results of this study, discuss various measures for reducing energy-transfer-upconversion and its effect on laser performance, and consider the prospects for further increase in output power and pulse energy.

We designed single-crystal fibers to combine excellent spectroscopic and thermo-mechanical properties of bulk crystals and ability of pump guiding and good heat repartition of doped glass fibers. Such single-crystal fibers of excellent optical quality were grown by the micro-pulling-down technique. A remarkable advantage of this technique is that pump guiding is achieved in the directly grown fiber without additional polishing on the cylinder. We designed 0.2%-Nd doped YAG crystal fibers sample of 50 mm and 1 mm diameter and AR coated on both end faces. It was longitudinally pumped by a fiber-coupled laser diode with a maximum output power of 120 W at 808 nm. Laser emission at 1064 nm was achieved inside a two concave mirrors cavity. We obtained 20 W of laser emission with a M² quality factor of 6, for an incident pump power of 120 W and a slope efficiency of 18% without any thermal management problems. Besides, a power of 16 W with linearly polarized laser emission has been obtained under the same pump power by introducing a thin plate polarizer in the cavity. An acousto-optical modulator was inserted inside the cavity and 360 kW of peak power with 12 ns pulses at 1 kHz repetition rate were achieved under 60 W of pump power. This work shows real improvements of laser performances in directly grown single crystal fibers. A complete thermal study confirms a good heat management and demonstrates scalability to high average power laser sources.

In the present work we present results of studies of hybrid sub-picosecond systems based on a solid-state Yb:KYW laser and a side-pumped fibre ytterbium amplifier manufactured using GTWave technology, which makes it possible to remove completely from the fibre amplification path any discrete optical elements. When the system was pumped with 12 W of CW radiation at 980 nm 0.9-ps output pulses with energy 40 nJ were generated at the repetition frequency of 100 MHz and the average radiation power 4 W. The centre wavelength of the system could be detuned within 1035-1055 nm (pulsed mode) and 1030-1070 nm (CW mode). Details are given of the layout of the femtosecond Yb:KYW laser developed with the use of saturable absorber mirror and chirped mirrors. For the first time gain coefficients of fibre GTWave Yb amplifier were measured within the generation range of the Yb:KYW laser. The developed system is a promising source of controlled super-continuum radiation, since the radiation pulse wavelength may be tuned around the zero dispersion wavelength of standard holey fibres (1040 nm) designed for super-continuum generation when pumped in this spectral range.

We report on recent advances in the performance of GaSb-based optically pumped semiconductor disk lasers (OPSDLs), emitting in the 2.0 - 2.3 μm wavelength range. Both barrier pumped OPSDL (using 980 nm laser diodes as pump source) and in-well pumped OPSDL (using 1.96 μm pump radiation) have been fabricated and characterized. Using alternative SiC or diamond intracavity heatspreader, multiple-watt CW-output powers have been achieved (e.g. >3W at 2.3 μm and >5W at 2.0 μm), with power efficiencies in the range of 18 % - 25 %. For an optimised resonator setup, the beam profile is close to the diffraction limit with M² values around 1.2; and even for the highest power levels, M² is in the range of 2-5.

Optically pumped semiconductor (OPS) vertical-external-cavity surface-emitting lasers (VECSELs) offer the first truly high-brightness high power laser sources with serious power scaling potential to multiple kW levels and flexible spectral coverage from IR to mid-IR. Due to the fact that the semiconductor chip (or subcavity) of a VECSEL serves as both the gain medium and a cavity mirror, the design and optimization of the semiconductor subcavity is key to achieve high power operation and consequently high power extraction via pump area scaling. A fundamental microscopic quantum design approach, allowing for calculating the electro-optical properties of QWs such as the optical gain/absorption and carrier recombination rates, is combined with a coupled optical-thermal-carrier analysis scheme to design and optimize VECSEL chips for wavelengths in the IR. We will describe the design and optimization procedure and present simulation results on VECSEL chips at wavelengths of 980 nm, 1178 nm, and 2 μm.

This presentation will overview the growth of an IMF based VECSEL structure operating at 2 μm with an InGaSb QW active region (a₀ = 6.09 Å) on GaAs/AlGaAs distributed bragg reflectors (DBR) (a₀ = 5.65 Å). The use of the GaAs substrate instead of GaSb results in a significant reduction in the surface defect density while allowing the use of a mature GaAs/AlGaAs DBR technology. We shall provide photoluminescence results from 2 μm IMF based active regions grown on GaAs substrates and compare the results with the same active regions grown on GaSb substrates. We shall also provide extensive transmission electron microscopy, surface morphology and high-resolution x-ray diffraction analysis of the material grown.

This work reports on an optically-pumped vertical external-cavity surface-emitting laser (VECSEL) emitting around 852 nm for Cesium atomic clocks experiments. We describe the design and the characterization of a VECSEL semiconductor structure suitable for these applications. The parameters of the structure have been optimized in order to have a low threshold and a high gain structure emitting around 852 nm. We achieved an output power of 330 mW for 1.1 W of incident pump power. We are able to simulate the laser emission variations with the temperature of the substrate, the pump radius on the semiconductor structure and the losses inside cavity. A compact and robust setup was built to obtain a stable single-frequency emission. We obtained a 17-mW single frequency emission exhibiting broad and fine tunability around the Cesium D₂ line.

Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor QW optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Current practice in amplifier or laser design assumes phenomenological parameterized models for these critical optical properties and has to rely on experimental measurement to extract model fit parameters. In this tutorial, I will present an overview of a powerful and sophisticated first-principles quantum design approach that allows one to extract these critical optical properties without relying on prior experimental measurement. It will be shown that an end device L-I characteristic can be predicted with the only input being intrinsic background losses, extracted from cut-back experiments. We will show that textbook and literature models of semiconductor amplifiers and lasers are seriously flawed.

Semiconductor Disk Lasers (SDLs) are compact lasers suitable for watt to multi-watt direct generation in the 670- 2350nm waveband and frequency-doubled operation in the ultraviolet and visible regions. This is, however, critically dependent on the thermal management strategy used as, in this type of laser, the pump is absorbed over micrometer lengths and the gain and loss are temperature sensitive. In this paper, we compare the two heat dissipation techniques that have been successfully deployed to-date: the "thin device" approach where the semiconductor active mirror is bonded onto a heatsink and its substrate subsequently removed, and the "heatspreader" technique where a high thermal conductivity platelet is directly bonded onto the active part of the unprocessed epilayer. We show that for SDLs emitting at 1060nm with pump spots of ~80µm diameter, the heatspreader approach outperforms the thin-device alternative, with the best results being obtained with a diamond heatspreader. Indeed, the thermal resistances are measured to be 4.9, 10.4 and 13.0 K/W for diamond-bonded, SiC-bonded and flip-chip devices respectively. It is also observed, as expected, that the thermal management strategy indirectly affects the optimum output coupling and thus the overall performance of these lasers.

Ultrashort pulse (USP) Ti:Sapphire oscillators are constantly improving in cost, performance, and reliability. These improvements have been driven in part by improvements in the CW lasers used to pump the Ti:Sapphire gain medium. Recent development of optically-pumped semiconductor (OPS) lasers heralds a USP pump source that reduces cost and complexity while maintaining a high standard of performance and reliability. OPS lasers offer significant advantages with respect to traditional diode-pumped solid state (DPSS) lasers in regards to wavelength flexibility, broad pump tolerance, efficient spectral and spatial brightness conversion and high power scaling. In this paper, we report the performance of different types of ultrashort pulse Ti:Sapphire oscillators pumped by OPS lasers: broad bandwidth (approximately 100 nm) negative dispersion mirror based, broad bandwidth (approximately 100 nm) prism based, and narrower bandwidth (approximately 10 nm) tunable prism based oscillator. We analyze the impact of multimode spatial mode operation of the OPS pump laser on the mode quality, bandwidth and intensity noise of the USP oscillator output. We compare the performance of USP oscillators pumped by multiple transverse mode OPS lasers with traditional single transverse mode Nd:YVO₄ DPSS lasers. We demonstrate excellent regenerative amplifier seeding with the OPS pumped Ti:Sapphire oscillator.

Among enabling key components for mobile laser projection, the green laser plays an outstanding role: We present green laser modules based on frequency doubled optically pumped semiconductor disk lasers. In these lasers with twofold conversion, from 808nm over 1060nm to 530nm, active semiconductor components and second harmonic generation have to be carefully optimized to realize good efficiency at moderate output powers. The concept was developed not only to meet power and efficiency targets, but also to provide simple operation and control by pump diode current. The latest concept targets green output powers of more than 50mW at wall plug efficiencies >7%, limiting total electrical power consumption to less than 1W. Consequent use of micro optical components allows for a package volume of less than 0.5cm³.

We present an air-cooled optically pumped semiconductor laser that provides a cw output power of 1W at 488 nm. This performance was achieved via intracavity frequency doubling at a laser diode pump power of 2.5 Watts. The increased efficiency was realized by optimizing the OPS chip design and improving the heat extraction from the OPS chip. Efficient cooling of the OPS chip and a compact and mechanically stable folded resonator provide maintenance-free long life laser operation with an M² of less than 1.1 and a noise of less than 0.25% rms. The size of the laser head is the same as for the 20 mW commercially available version, namely 125 x 70 x 34 mm.

Optically pumped semiconductor vertical-external-cavity surface-emitting laser (VECSEL) potentially provides an innovative approach to low-cost frequency agile lasers engineered for specific applications in infrared and visible range. In this paper, we report on the development and demonstration of a multi-Watt highly strained InGaAs/ GaAs vertical-external- cavity surface-emitting laser (VECSEL), which can be tuned from 1147 nm to 1197 nm. Based on this tunable InGaAs/GaAs VECSEL and intracavity frequency doubling, we develop multi-Watt frequency-doubled tunable VECSEL in a wide yellow-orange band (579 ~595 nm). This compact high-power yellow-orange laser provides an innovative approach to an affordable guidestar laser (~589.1 nm) solution, and has a lot of important applications in biomedicine.

Owing to their good beam quality and high output power, near-infrared semiconductor disk lasers provide an attractive opportunity for visible light generation via frequency conversion. The typical cavity arrangement of a semiconductor disk laser, consisting of a semiconductor multiple quantum well gain mirror and one or more external mirror, offers a convenient configuration for intracavity frequency doubling. Recent progress in the disk laser development has led to demonstrations of multi-watt green-blue-yellow sources. These achievements have been enabled by the possibility to integrate high performance InGaAs/GaAs gain media and Al(Ga)As/GaAs Bragg reflectors operating in the 940-1160 nm wavelength range. In order to achieve ~620 nm red emission, a laser emitting near the fundamental wavelength of 1240 nm is needed. To achieve this spectral range we have developed GaInNAs/GaAs gain mirrors and we have achieved 1 W of output power at 617 nm by frequency doubling in a BBO crystal. This is to our knowledge the highest power reported to date for intracavity doubled disk laser based on dilute nitride gain material.

We present a CPA-free picosecond laser that will pave the way to cost effective industrial micromachining by operating not only at high pulse energy but also at significantly higher average output power than previously achieved in commercial ultrafast systems. The laser is based on a regenerative amplifier using a state-of-the art thin-disk laser head, and includes an external modulator for user-adjustable pulse energy. 80 W of average power are demonstrated at a repetition rate of 200 kHz and a duration of about 7 ps.

A directly diode pumped Yb:KYW regenerative amplifier is demonstrated to study a novel approach to enhance the gain bandwidth. Two gain spectra are combined by using the crystal directions Nm and Np of Yb:KYW.

We report on the development of a Nd:YVO4 based regenerative amplifier, producing more than 25W of average power at 200kHz, with a pulse length of 10ps at 1064nm. The amplifier is seeded by a low power, mode-locked fiber laser. The amplifier output has been used for the generation of high energy second and third harmonics with up to 80% conversion to 532nm and 40% to 355nm. The average power of the amplifier has been increased further using a single pass linear amplifier to produce 54W at 200kHz.

This paper discusses the hydrothermal synthesis of doped and undoped Sc₂O₃ single crystals as well as Y₂O₃ and Sc₂O₃ nanoparticles as high purity precursors to polycrystalline laser hosts.

Edge-pumping Nd:YAG laser gain media is a convenient method to couple pump power into a laser cavity. A difficulty with this geometry is that for uniformly doped materials, pump power deposited near the edge of the gain medium cannot be efficiently extracted by a diffraction-limited beam. However, ceramic Nd:YAG with smooth changes in neodymium doping level (doping profiles) can now be fabricated to ameliorate this problem. A slab engineered with a doping profile that has a higher concentration of Nd in the center, and less at the edges, would allow more pump power to be efficiently extracted by a diffraction-limited laser beam. Yet this solution poses its own problem because variations in Nd concentration introduce optical path length distortions that can significantly reduce beam quality. The variations in optical path length are predominantly from changes in the refractive index of the host due to Nd doping and spatially varying temperatures. A genetic-algorithm-based approach is presented that balances improvement in mode-overlap between excited state distribution and the signal laser beam against optical path length distortions. A doping profile was found for an edge-pumped, zig-zag slab amplifier that is expected to yield a 39% improvement in extracted power delivered into a diffraction-limited spot compared to a uniformly doped slab.

The lack of blue pump sources for Pr-doped materials has been overcome with the recent progress in optically pumped semiconductor lasers (OPS) operating at 479 nm. The availability of reliable high power OPS pump lasers, makes Pr³⁺-doped crystals ideal gain media for compact and efficient ultraviolet solid-state lasers with output power in the Watt range. We report on the scalability of a 522/261 nm Pr:YLF cw laser that is dual-end-pumped by two OPS lasers at 479 nm. At 9.6 W of incident pump power more than 4 W were obtained at 522 nm with a slope efficiency of 45%. Intracavity frequency doubling of 522 nm resulted in 1 Watt of cw UV output at 261 nm.

Diode lasers provide a high degree of flexibility in signal shaping. Picosecond pulses with repetition rates from single shot to 80 MHz or arbitrary modulation formats with GHz bandwidth can be achieved through appropriate electrical drivers without changing the optical configuration. The limitations, however, of single mode diode lasers are low (mW) power levels and a lack of emission wavelengths between 470 and 630 nm. Optical amplification can extend single mode diode lasers to higher power levels where frequency doubling becomes a suitable option e.g. for producing green light at 530 nm. Ytterbium-doped fiber amplifiers (YDFA) show robust and stable operation at 1064 nm with amplifications of about 20 dB. We present a fiber amplified and frequency doubled diode laser that emits green picosecond pulses at variable repetition frequencies with an average output power of several milliwatts. Compared to existing semiconductor-amplified systems, higher stability at significantly smaller size and lower power consumption is achieved.

In common intra-cavity SHG schemes, the requirement for high(st) level of fundamental frequency power inside the non-linear crystal contradicts with the condition for extracting the maximum power available from the laser active medium. This impedance mismatch problem is removed by using the fundamental frequency power enhancement in two steps, the first one being optimized for maximum power outcoupling while at the second step the circulating inside nonlinear crystal power is further increased for maximum efficiency of SHG process. Experimentally proved this approach allows 3-5 times higher SH output power from DPSS lasers at given pump as compared with traditional schemes.

Optimization of nonlinear coupling and use of aggressive Q-switch clipping on the pulse falling edge has enabled high beam quality, internally frequency-converted, Nd:YAG lasers with output powers greater than 35 W at both green and ultraviolet wavelengths. By retaining more energy in the rod after the pulse, such lasers operate with enhanced gain levels and achieve greater nonlinear conversion. Operation in this gain-enhancement regime has enabled lasers with highly variable pulse-widths. We demonstrate here that gain-enhanced laser operation with variable pulse energy and/or delay between pulses is also possible. This combination of features and flexibility available in gain-enhanced, frequency-converted lasers allows optimization of laser processing for a wide range of candidate materials.

We present what is, to the best of our knowledge, the first experiment of intracavity pumping at 914 nm of an Yb:SFAP crystal emitting at 985 nm on the three-level laser transition. This configuration enabled us to indirectly diode-pump this ytterbium doped crystal, and to obtain 1.4 W output power at 985 nm for 20 W of incident pump power at 808 nm. Intracavity second harmonic generation has also been demonstrated in a KNbO₃ crystal with a total of 120 mW linearly polarized output power at 492.5 nm on two output beams.

We present the diode pumping of a Nd-doped strontium and lanthanum (Nd:ASL) crystal Sr_1-xLa_x-yNd_yMg_xAl_12-xO₁₉ (0.05 ≤ x ≤ 0.5; y = 0.05) for second harmonic generation around 450 nm. In order to fulfill the pumping requirements of this crystal, we have developed a high-brightness pump source based on a tapered amplifier in an extended cavity with a volume Bragg grating for wavelength stabilization. A pump brightness of 110 MW.cm^-2sr^-1 has been obtained with a linewidth lower than 80 pm at 798 nm. This laser source has been used to pump a Nd:ASL crystal to obtain 300 mW at 906 nm and 53 mW at 453 nm by intracavity doubling with a LBO crystal.

The CW diode-pumped alkali laser (DPAL) based on the rubidium resonance transition at 794.8 nm has been investigated. The pump sources for these experiments are commercially available 780 nm fiber-coupled diode modules, incorporating volume holographic gratings for wavelength control. Operating characteristics, pump architecture, power scaling and lifetime limitations have been studied. To date, lasers pumped by single 20 W diode bars have produced over 1 W output at 794.8 nm and 100 mW at the 397.4 nm harmonic. Lasers pumped by two 40 W diodes generate almost 8 W at 794.8 nm.

We present a ring laser system that offers convenient exchange between titanium:sapphire and dye operation. Different approaches reduce the short-term linewidth of the system, such as lock to the side of a fringe of a reference etalon and using a Pound-Drever-Hall scheme, can be used for both configurations and are evaluated. Furthermore, titanium:sapphire and dye versions are compared regarding: efficiency, tuning range, linewidth, single-mode scan range, amplitude-noise and second harmonic generation.

Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser. The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.

Thulium doped vanadates Tm:YVO₄ (5 at.% Tm/Y, grown by the Czochralski technique), Tm:GdVO₄ (2 and 6 at.% Tm/Gd, grown by the floating-zone technique), and Tm:LuVO₄ (3 at.% Tm/Y, grown by the floating-zone technique) were investigated as an active medium for diode pumped tunable laser operating around 1.9 μm. For thulium laser tuning single 1.5mm thick Brewster-angled birefringent quartz plate (Lyot filter) was placed in simple 80mm long linear quasi-hemispherical resonator. For thulium doped vanadates pumping a fibre-coupled (core diameter 400 μm) temperature-tuned laser diode operating in range from 799 up to 810nm was used (max available power 20 W). All tested crystals were investigated under CW and pulsed pumping. Under pulsed pumping (4% duty-cycle, reduced heat generation) lasing and laser tuning was demonstrated with all available samples. Lasers were tunable in following wavelength ranges: Tm:YVO₄ 5 at.% Tm/Y (1841 - 1927 nm), Tm:GdVO₄ 2 at.% Tm/Gd (1830 - 1982 nm), 6 at.% Tm/Gd (1850 - 2010 nm), and Tm:LuVO₄ 3 at.% Tm/Lu (1860 - 1940 nm). Under CW pumping only Tm:GdVO4 crystal was lasing (lasing of Tm:YVO4 and Tm:LuVO₄ was not reached under elevated pumping duty factor). Using Tm:GdVO₄ (2 at.% Tm/Gd) the power up to 2.6W and slope effciency ~ 30% (with respect to absorbed power at 808nm under lasing condition) was obtained at wavelength 1.91 μm. Tunable operation with greater that 1W output and 130nm tuning range (1842 - 1972 nm) was demonstrated for Tm:GdVO₄ (2 at.% Tm/Gd) pumped at 802 nm.

Daylight Solutions is currently developing field deployable, high power, wavelength agile, external cavity quantum cascade lasers (EC-QCLs). These devices are finding uses as IR sources for applications such as remote gas sensing, imaging, and illumination. Progress in three specific areas of development will be discussed: (i) miniaturization of a fast tunable, moderate resolution, pulsed QCL for gas sensing, (ii) demonstration of high power mod hop free tunable CW QCL's for high resolution spectroscopy, and (iii) progress in development of battery powered high efficiency fixed wavelength EC-QCL light sources for molecular imaging and detection.

Highest precision and minimal thermal impact is achieved, using picosecond laser pulses for micromachining. Virtually any material can be processed with outstanding quality. The use of ultraviolet (UV) pulses can provide additional benefits in higher throughput and improved edge quality for materials like metals, glasses, semiconductors or ceramics. The advanced oscillator-amplifier (MOPA) laser design, based on reliable Nd:YVO₄-systems, enables power scaling of IR-pulses, and led to a series of laser systems with a repetition rate as high as 1 MHz and average power levels ranging from 10 W to well above 50 W. Harmonic generation to the visible (532 nm) and the UV (355 nm) reaches efficiencies of 50%, providing powerful beams for cost effective high-speed micromachining with high throughput.

Advanced semiconductor logic devices are increasingly complex, typically composed of multiple layers of dielectric, metal, and semiconductor materials. Laser micromachining is employed on these devices to form cut-outs, microvias, and perform partial material removal, including scribing and dicing operations. The recent development of high average power (> 10 W), < 20 ps, 1064 nm diode-pumped mode-locked solid state lasers, operating at pulse repetition frequencies > 100 KHz, enables an attractive short pulsewidth laser process alternative to existing nanosecond process technologies, particularly for laser micromachining of complex alloy structures. Emerging 45 and 65 nm node logic devices may contain greater than eight metal layers, typically aluminum and copper. They may also contain advanced low K layers which have proven difficult to process using conventional mechanical techniques, such as dicing saws. Efficient operation at 355 nm was readily achieved using extracavity conversion by employing non-critically phasematched LBO for SHG and critically phase-matched LBO for THG. Over 3 W at 355 nm at 100 KHz was achieved with an input of 8.5 W at 1064 nm. Preliminary micromachining results on advanced logic devices containing multiple low k and Cu layers at harmonic wavelengths (532 nm and 355 nm) yielded micromachining rates of > 300 mm/s with good workpiece quality.

It has been shown that micromachining of polymer materials using mode-locked, high repetition rate, 355nm picosecond lasers is more efficient in respect to ablation rates and processing speeds, than using q-switched lasers at the same wavelength and same average power level. In this study we present a systematic comparison of application results obtained with q-switched nanosecond and mode-locked picosecond ultraviolet (UV) lasers. From the results, guidelines are derived as to which laser type to use for best results depending upon material type and thickness. Additionally, recent results obtained using a high power mode-locked UV picosecond laser - the Pantera^TM - are described, along with implications of how scaled-up power can significantly enhance processing efficiency in manufacturing environments.

In this talk we will present a novel glass processing technique using q-swicthed INNOSLAB lasers. The mJ laser beam of some ns pulse length and beam quality of M² < 1,3 from INNOSLAB laser is focused into the glass to a very small spot. Because of the nonlinear absorption at high intensity the laser energy is absorbed near the focus. This leads to micro cracks inside glass or localized ablation, if the focus is on the glass surface. Using this mechanism glass can be proceeded at high precision and speed.

Increased homeland security concerns across the world have generated a strong demand for forgery-proof ID documents. Manufacturers currently employ a variety of high technology techniques to produce documents that are difficult to copy. However, production costs and lead times are still a concern when considering any possible manufacturing technology. Laser marking has already emerged as an important tool in the manufacturer's arsenal, and is currently being utilized to produce a variety of documents, such as plastic ID cards, drivers' licenses, health insurance cards and passports. The marks utilized can range from simple barcodes and text to high resolution, true grayscale images. The technical challenges posed by these marking tasks include delivering adequate mark legibility, minimizing substrate burning or charring, accurately reproducing grayscale data, and supporting the required process throughput. This article covers the advantages and basic requirements on laser marking of cards and reviews how laser output parameters affect marking quality, speed and overall process economics.

Ultra-short-pulse solid-state laser sources have improved contrast within fluorescence imaging and also opened new windows of investigation in biological imaging applications. Additionally, the pulsed illumination enables harmonic scattering microscopy which yields intrinsic structure, symmetry and contrast from viable embryos, cells and tissues. Numerous human diseases are being investigated by the combination of (more) intact dynamic tissue imaging of cellular function with gene-targeted specificity and electrophysiology context. The major limitation to more widespread use of multi-photon microscopy has been the complete system cost and added complexity above and beyond commercial camera and confocal systems. The current status of all-solid-state ultrafast lasers as excitation sources will be reviewed since these lasers offer tremendous potential for affordable, reliable, "turnkey" multiphoton imaging systems. This effort highlights the single box laser systems currently commercially available, with defined suggestions for the ranges for individual laser parameters as derived from a biological and fluorophore limited perspective. The standard two-photon dose is defined by 800nm, 10mW, 200fs, and 80Mhz - at the sample plane for tissue culture cells, i.e. after the full scanning microscope system. Selected application-derived excitation wavelengths are well represented by 700nm, 780nm, ~830nm, ~960nm, 1050nm, and 1250nm. Many of the one-box lasers have fixed or very limited excitation wavelengths available, so the lasers will be lumped near 780nm, 800nm, 900nm, 1050nm, and 1250nm. The following laser parameter ranges are discussed: average power from 200mW to 2W, pulse duration from 70fs to 700fs, pulse repetition rate from 20MHz to 200MHz, with the laser output linearly polarized with an extinction ratio at least 100:1.

Photovoltaic energy conversion devices are on a rapidly accelerating growth path driven by increasing government and societal pressure to use renewable energy as part of an overall strategy to address global warming attributed to greenhouse gas emissions. Initially supported in several countries by generous tax subsidies, solar cell manufacturers are relentlessly pushing the performance/cost ratio of these devices in a quest to reach true cost parity with grid electricity. Clearly this eventual goal will result in further acceleration in the overall market growth. Silicon wafer based solar cells are currently the mainstay of solar end-user installations with a cost up to three times grid electricity. But next-generation technology in the form of thin-film devices promises streamlined, high-volume manufacturing and greatly reduced silicon consumption, resulting in dramatically lower per unit fabrication costs. Notwithstanding the modest conversion efficiency of thin-film devices compared to wafered silicon products (around 6-10% versus 15-20%), this cost reduction is driving existing and start-up solar manufacturers to switch to thin-film production. A key aspect of these devices is patterning large panels to create a monolithic array of series-interconnected cells to form a low current, high voltage module. This patterning is accomplished in three critical scribing processes called P1, P2, and P3. Lasers are the technology of choice for these processes, delivering the desired combination of high throughput and narrow, clean scribes. This paper examines these processes and discusses the optimization of industrial lasers to meet their specific needs.

We report on recent advances in the development of a 1064 nm pulsed master oscillator fiber power amplifier (MOFPA) with integrated modulators enabling programmable temporal pulse shapes and its employment in a tandem photonic amplifier. The MOFPA amplifier chain is seeded by a laser diode operated in the CW regime, yielding very stable spectral characteristics that are independent of the pulse repetition rate and pulse shape. The use of 3 GHz integrated LiNbO3 electro-optic modulators in conjunction with high speed digital electronics results in an excellent pulse shaping capability, a fine pulse amplitude stability and high repetition rate operation (100 kHz-1MHz) with fast rise times (<1ns). Energy per pulse of 8-10 μJ with good beam quality characteristics are obtained using advanced large mode area (LMA) fiber designs in the final power amplifier stage. The output is linearly polarized with a spectral bandwidth of < 0.1 nm. When employed in a tandem amplifier configuration, in which the MOFPA output is input to a single-stage, single-pass Nd:YVO₄ amplifier pumped by a single 30 W fiber-coupled 808 nm diode, a 600 mW average power at 100 KHz signal input from the MOFPA was amplified to 6 W with faithful amplification of the input temporal pulse profile while achieving excellent beam quality (M²<1.1) and pulse amplitude stability (< ±3%, 3σ). A model of tandem amplifier performance shows good agreement with experimental results and indicates prospective performance of advanced tandem photonic amplifier configurations.

High laser power levels combined with increasing beam quality bring optics performance into focus. The subject of optics performance is a hot topic, but lack of a common nomenclature, as well as of proper measurements, makes the situation confusing. This paper will introduce a nomenclature for comparing the performance of different types of optics. Further, the paper will present a test setup for characterizing optics, along with test results for different optics materials and designs. The main influence of high power levels on optics is a focal shift along the optical axis. In industrial applications, this might influence the performance of the process, especially if the focal shift is in the range of the Rayleigh length. In the test setup that is to be presented, the optics are exposed to a high power beam, and a pilot beam is used for measuring the change in focal position. For a proper description of optics performance, the laser beam parameters should not influence the measured results. In the nomenclature that will be presented, the performance is related to the Rayleigh length for a fundamental mode beam. The performance of optics when used with multimode beams will be presented.

Latest advances in femtosecond technology have strongly emphasized the control of ultra-short pulses in many applications where the preservation of the pulse duration is most important. Recently, the delivery of ultra-short pulses through optical fibers has become possible which opens up remarkable chances for simplifying optical setups or reaching inaccessible regions. In this study we report on fiber delivery of 2 nJ and sub 65 fs pulses from a Ti:Sapphire laser through 1.5 m LMA photonic crystal fiber. Application of such a fiber in an all-integrated THz imaging system to obtain contactless information on the doping concentration of semiconductor wafers is shown.

Yttrium and Lutecium garnets (YAG and LuAG) doped by Chromium or Vanadium ions (Cr⁴⁺ or V³⁺) were investigated as saturable absorbers potentially useful for passive Q-switching at wavelengths 1 μm and/or 1.3 μm. For comparison also color center saturable absorber LiF:F^-₂ and Cobalt doped spinel (Co:MALO) were studied. Firstly, low power absorption spectra were recorded for all samples. Next, absorbers transmission in dependence on incident energy/power density was measured using the z-scan method. Crystals Cr:YAG, Cr:LuAG, V:YAG, and LiF:F^-₂ were tested at wavelength 1064 nm. Therefore Alexandrite laser pumped Q-switched Nd:YAG laser was used as a radiation source (pulse length 6.9 ns, energy up to 1.5 mJ). Crystals V:YAG, V:LuAG, and Co:MALO were tested at wavelength 1338 nm. So diode pumped Nd:YAG/V:YAG microchip laser was used as a radiation source (pulse length 6.2 ns, energy up to 0.1 mJ). Using measured data fitting, and by their comparison with numerical model of a "thick" saturable absorber transmission for Q-switched Gaussian laser beam, following parameters were estimated: saturable absorber initial transmission T₀, saturation energy density w_s, ground state absorption cross-section σ_GSA, saturated absorber transmission T_s, excited state absorption cross-section σ_ESA, ratio γ = σ_GSA/σ_ESA, and absorbing ions density. For V:YAG crystal, a polarization dependence of T_s was also investigated. With the help of rate equation numerical solution, an impact of saturable absorber parameters on generated Q-switched pulse properties was studied in plane wave approximation. Selected saturable absorbers were also investigated as a Q-switch and results were compared with the model.

For effective conversion of the energy of the concentrated solar flux of 1 MW Big Solar Furnace of the Scientific and Production Association "Physics-Sun" (Tashkent) with focal spot size of about 40 cm into the coherent laser radiation, the several designs of the multi-element secondary concentrators for various active mediums with different thermal and optical characteristics were considered. For calculations of parameters of secondary concentrators the Ray tracing and Monte-Carlo methods were used and the numerical experiments were performed.

Monoclinic potassium double tungstates are biaxial laser materials characterized by strong anisotropy of the spectroscopic properties. KLu(WO₄)₂ is the most attractive of them in the case of Yb-doping because of the close ionic radii of Yb and Lu. In this work we compare crystals of equal dimensions and doping level but different cuts, under the same pumping conditions. Special emphasis is placed on the polarization behavior. We present substantial power scaling with KLu(WO₄)₂ in the continuous-wave regime by longitudinal fiber-coupled diode laser pumping. Slope efficiency of roughly 80% is achieved while the naturally selected laser polarization is parallel either to the N_p or N_m principal optical axes. A maximum output power of 11.0 W was produced from a 2 mm thick uncoated crystal with N_g-cut, the corresponding optical-to-optical efficiency was 68%.

Recently, fabrication of new laser materials with broadband absorption spectrum by ceramic technology allowed to receive the effective generation of coherent lights at lamp pumping. Due to this has appeared the new perspective opportunities for creation of high-efficient solar pumped lasers on the Nd³⁺:Cr³⁺:YAG ceramics. In this paper the possibility of application of the Nd³⁺:Cr³⁺:YAG ceramics for pumping by concentrated solar flux of the Big Solar Furnace with 1 MW power is considered.

In the present paper it has been demonstrated that the suggested and for the first time experimentally tested method for considerable reduction in long-term radiation frequency drift of CW single-frequency Ti:Sapphire and dye lasers based on a fast high-precision radiation wavelength meter and a digital-analogue feed-back system can present an efficient alternative to conventional methods for long-term frequency stabilisation. Long-term frequency drift of the lasers was improved from ~450 MHz/h in free-running regime to less than 40 MHz/h in the regime of frequency stabilisation. Application of a wavelength meter as a spectral reference allows reduction in the long-term frequency drift down to the level of residual drift inherent in the wavelength meter. An interesting prospective feature of the suggested method is the possibility to use a wavelength meter for periodical operative wavelength correction of more than one laser, which can also be performed remotely when a laser and the wavelength meter are connected with a long optical waveguide and the wavelength value is transmitted though the Internet. The proposed method of stabilisation can be used for single-frequency lasers of any type (solid-state, diode, fibre, dye lasers, etc.), in which continuous controlled radiation frequency detuning is possible.

A passively Q-switched diode-laser pumped ceramic Nd:YAG laser has been constructed and the output characteristics has been investigated. The output efficiency of 36.1 % has been obtained with 1.1 at.% of neodymium concentration in the ceramic YAG. For the case of neodymium concentration of 2.0 at.%, the output power decreases as the pump power increases over 6 W. The output power has rapidly decreased more than 10 W of pumping, and the laser output has finally disappeared at pumping power of 13 W. This phenomenon can be explained by the thermal lens effect in the laser material. Passive Q-switching has been carried out using a Cr:YAG crystal in the resonator. The pulse width is 61.2 ns and the repetition rate is 10.1 kHz at the pump power of 1 W. The beam propagation factor M² has been measured to be 1.2, which shows good beam quality of the Q-switched pulse.

The efficient stimulated Raman scattering conversion in a diode-pumped actively Q-switched Nd:YAG laser was achieved with an undoped YVO₄ crystal as a Raman shifter. With an incident pump power of 16.2 W, 1176-nm first Stokes average output power of 2.97 W was generated at a pulse repetition rate of 50 kHz. The maximum pulse energy is higher than 83 μJ at both 20 kHz and 30 kHz. With mode-locked modulation, the effective pulse width far above threshold is usually below 5 ns. With an incident pump power of 7.62 W, the peak-power of 43.5 kW was demonstrated at 20 kHz.

We report a high-peak-power AlGaInAs 1.36-μm vertical-external-cavity surface-emitting laser (VECSEL) optically pumped by a diode-pumped actively Q-switched Nd:GdVO₄ 1.06-µm laser under room-temperature operation. The gain medium is an AlGaInAs quantum wells (QWs)/barrier structure grown on a Fe-doped InP substrate by metalorganic chemical-vapor deposition. With an average pump power of 1.9 W, an average output power of 340 mW was obtained at a pulse repetition rate of 40 kHz, corresponding to an optical-to-optical conversion efficiency of 18.76%. With a peak pump power of 7.9 kW, the highest peak output power was 1.3 kW at a pulse repetition rate of 10 kHz.

Progress in the development of efficient and reliable diode-pumped ytterbium femtosecond laser systems based on Kerr-lens mode locking effect is reported. Average output power of up to 1 W is demonstrated in a Kerr-lens mode locked Yb:YVO₄ laser with pulse durations as short as 80 fs at a pulse repetition frequency of 79 MHz. Measurements of the nonlinear refractive indexes of the Yb³⁺:YVO₄ crystal, n₂, were performed and were determined to be 39×10^-16 cm²/W and 49×10^-16 cm²/W for E||c and E⊥c polarizations, respectively. These results were found to be in a good agreement with those calculated using both the Kramers-Krönig relation and Boling, Glass and Owyoung formula. Keywords: Mode-locked lasers, diode-pumped lasers 1.

We demonstrate an AlGaInAs saturable absorber with a periodic quantum wells (QWs)/barrier structure that can be used to achieve an efficient high-peak-power and high-pulse-energy passively flashlamp-pumped Q-switched Nd:YAG laser at 1.06 um. The barrier layers are designed to locate the QW groups in the region of the nodes of the lasing standing wave to avoid damage. With an incident pump voltage of 14.5 J, a single pulse was generated with a pulse energy of 14 mJ and a Q-switched pulse width of 13 ns. The maximum peak power was greater than 1.08 MW.

Pulsed tunable diode-pumped Tm:YAP laser was characterized and used for preliminary investigation in eye microsurgery. By means of Lyot filter, the laser emission was tuned between a high (120 cm^-1 @ 1940 nm) and two times lower (50 cm^-1 @ 2040 nm) value of radiation absorption in water. In the interaction experiment, the eye tissue (in vitro) was irradiated with tunable Tm:YAP laser radiation, and the effects of cutting and coagulation depth in wavelength range from 1940 nm up to 2040 nm were investigated. The results were documented by optical microscope.

Sensitive, real-time chirp and spectral phase diagnostics along with full field reconstruction of femtosecond laser pulses are performed using a single rapid-scan interferometric autocorrelator. Single shot diagnostics are possible when the second-harmonic spectrum is available. A novel graphical representation distinguishes between temporal and spectral phase distortions. Examples are presented that illustrate the sensitivity and fidelity of the scheme even with low signal-to- noise.

Pumped by a Q-switched Nd:YAG laser operating at 1064 nm and its frequency-doubled 532 nm, a maximum energy of 2.5 mJ and a tuning range of 1206-1315 nm were obtained experimentally for a forsterite laser at room temperature. A theoretical analysis and calculation including the tunable and output characteristics of this chromium-doped forsterite laser is presented in this paper.

We present LIBS experimental results that demonstrate the use of a newly compact, versatile pulsed laser source in material analysis in view of research aiming at the development of portable LIBS instrumentation. LIBS qualitative analyses were performed on various samples and objects, and spectra were recorded in gated and non-gated modes. The latter is important because of advantages arising from size and cost reduction when using simple, compact spectrograph-CCD detection systems over the standard ICCD-based configurations. The new Nd³⁺:YAG laser source exhibited very reliable performance in terms of laser pulse repeatability, autonomy and interface. Indeed, it can deliver a 45 mJ for 4.5 ns pulse and work at 1 Hz. Having the ability to work in double-pulse mode, it provided versatility in the measurements leading to increased LIBS signal intensities, improved the signal noise ratio and stabilized spectra. The first test results are encouraging and demonstrate that this new laser is suitable for integration in compact, portable and low cost LIBS sensors with a wide spectrum of materials analysis applications.

We report a simple method for fabricating transition metal (TM) doped II-VI powders with average size of about 10- 20μm as well as room temperature mid-infrared (2-3 μm) random lasing based on Cr²⁺-doped ZnSe and ZnS powders prepared without crystal growth stage under optical intra-shell excitation of chromium. Fabrication of Cr²⁺-doped ZnSe and ZnS powders involved two simple stages. At the first stage, pure ZnSe, (ZnS) and CrSe, (CrS) (with a concentration of Cr²⁺ ion 2×10^-19 cm^-3 and 5 × 10^-19 cm^-3 for ZnSe and ZnS respectively) chemicals with an average grain size of 10μm were uniformly mixed by means of a mechanical shaker. At the second stage the obtained ZnSe/CrSe mixture was sealed into evacuated (~10-4 Torr) quartz ampoule and annealed either at 1200°C for 15 minute, or 1000°C for 3 days. In the case of ZnS/CrS mixtures the annealing was performed in evacuated quartz ampoule at 1000 °C for 14 days. After annealing, under 1560 nm excitation, the powders demonstrated room temperature middle-infrared luminescence of Cr²⁺ similar to Cr²⁺ emission in bulk ZnSe and ZnS. Moreover, the output-input characteristic clearly demonstrated the threshold-like behavior of the output signal with the threshold pump energy density of ~44.5 mJ/cm² ~7.46 mJ/cm², and 63.6 mJ/cm² for Cr:ZnSe annealed for 15 min, 3 days, and Cr:ZnS respectively.

The tetragonal double tungstates NaGd(WO₄)₂ and NaY(WO₄)₂ are uniaxial crystals which can be grown from the melt by the Czochralski method and exhibit disordered crystalline structure. The structural disorder leads to additional inhomogeneous broadening of the spectral features of the doping rare-earth ions. We report on passive Q-switching of Yb:NaGd(WO₄)₂ and Yb:NaY(WO₄)₂ lasers operating near 1 μm using a Cr⁴⁺:YAG saturable absorber in a simple, diode end-pumped plano-concave resonator. With both crystals average powers of roughly 2 W were obtained for pulse durations of ≈30 ns and single pulse energy of ≈150 μJ at kilohertz repetition rates (roughly from 1 kHz to above 10 kHz). The maximum slope efficiency achieved in the Q-switched mode of operation was 40%.

The objective of this study is to determine feasibility of ternary Fe:CdMnTe crystals for room temperature lasing in the mid-infrared spectral range. Fe:CdMnTe samples were grown with a modified Bridgman technique. At room temperature, Fe:CdMnTe features wide (2800-6000nm) absorption and emission (3700-6500nm) bands. The kinetics of the photoluminescence were measured over 14K-300K temperature range under 2920nm and 532nm excitation. The low temperature (14K) kinetic of luminescence under 2920nm excitation was a single exponential with a decay time of 75μs. The room temperature emission cross-section was estimated to be 2x10^-18cm².

One of the ways to increase the concentrating ability of solar concentrators used for pumping of lasers is an additional concentration of a sunlight by a secondary concentrator allocated in a focal area of the primary concentrator. Limiting concentrations of those compound systems on the basis of non-imaging optics have been received by Winston. However more detailed calculations on the basis of irradiance integral are necessary for designing and practical realization of such systems. It is especially important for the systems including generally compound of two secondary concentrators. The full design procedure for concentration by systems of type compound parabolic concentrator or Winston concentrator (focon) and a cone concentrator is developed in the work in view of real distribution of brightness on a solar disk and discrepancies of primary concentrator geometry. The generalized dependences of efficiency of compound systems for the maximal and mean concentration in a focal plane of the primary paraboloidal concentrator depending on its disclosing angle U₀ and discrepancies of geometry are received. It is shown, that focon only up to U₀ < 30° is more effective, than the cone and further their efficiencies are identical. It is shown, that secondary concentrator allows to increase the pumping efficiency not less, than 30%.

We experimentally investigate phase synchronization between two detuned response chaotic laser systems coupled to a slightly different drive oscillator. Our result is that phase synchronization can occur between response laser systems when they are electronically driven by correlated (but not identical) inputs from the drive oscillator. We call this phenomenon generalized phase synchronization and clarify its characteristics using temporal behaviors and phase portraits.