An overview of cw lasers emitting in the blue (440nm - 495nm) and in the green wavelength range (505nm - 540nm) is given. Different architectures, including diode-pumped solid state lasers, fiber lasers, and semiconductor lasers, are compared in regards to laser performance, accessible power levels and emission wavelengths, and their use in industrial and scientific applications.

Frequency conversion of near-infrared diode lasers provides an efficient method to generate tunable laser radiation in the near-UV, violet and blue-green spectral range. High-power, coherent fundamental laser sources such as master oscillator-power amplifier (MOPA) configurations are now state of the art and commercially available. A new, highly efficient material for second-harmonic generation (SHG) is Bismuth Triborate ("BiBO", stoichiometry BiB3O6). The material has a high effective non-linearity d_eff, is non-hygroscopic and transparent for wavelengths between 286 nm and 2.5 μm. Compared to other non-linear crystals, "walk-off" effects between fundamental laser radiation and frequency-doubled beam are considerably lower. We used a BiBO crystal in a resonant doubling cavity to convert the output of a 780 nm, 900 mW tapered amplifier system. A maximum UV power of 400 mW (conversion efficiency 44%) was attained. This value is 3-4 times higher than previous results obtained with LBO or BBO crystals and, to the best of our knowledge, represents the highest tunable cw power of a frequency-converted diode laser.

We report a simple and compact all-solid-state laser generating 488 nm light with continuously variable output power in the range from 1 mW to over 120 mW. We frequency double single frequency radiation from an external cavity semiconductor laser in a periodically poled MgO:LiNbO₃ ridge waveguide. The laser maintains a high quality TEM₀₀ circular beam with M² < 1.1 and very low r.m.s. noise of less than 0.06% over the entire range of output power. Less than 0.1% peak-to-peak output power variation was measured during 14 hours of operation. No degradation of the conversion efficiency has been observed for operation at an output power of 70 mW for 3.5 months. The prototype laser has a small footprint of 5x8 cm.

Optically pumped semiconductor material is a complimentary gain medium for rare earth or transition metal doped crystals. The design of several compositions based on GaAs allows the realization of a wavelength range between 710nm and 1180nm. This can be diode pumped and frequency doubled to cover the near UV up to the yellow spectral range. The power is scaleable and we have realized several Watts at 488nm and 460nm. Experimental results will be presented and discussed as well as reliability data to show that this technology has ripened for industrial applications.

We describe a passively mode-locked, diode-pumped Nd:YAG laser that is used for frequency-conversion applications. The laser is based on a Direct-coupled Pump gain element and saturable Bragg reflector. The laser produces a 20-ps pulse with a 100-MHz repetition rate in a compact commercial package. It has typically <0.2% amplitude noise and diffraction-limited output beam. The average power is typically 7-8 W, and peak power is 4 kW which makes it well-suited for efficient frequency conversion. Using 2 stages of LBO for cascaded second-harmonic and sum-frequency generation, we have obtained >1 W at 355 nm. In addition, we have generated super-continuum output in the visible and infrared from micro-structured nonlinear fiber with pumping both at 1064 nm and 532 nm. Current applications for this laser, primarily in the ultraviolet, include flow cytometry, stereolithography, and semiconductor inspection.

In this paper we discuss the design and performance of high-density microlaser devices we have been developing, including a series of compact Nd:Vanadate lasers operating at 1064 and 532 nm, and miniature green lasers producing 1-100 mW single-transverse-mode output at 532 nm. In particular, our miniature green lasers have been designed and tested in both 9 mm and 5.6 mm industry standard modified TO cans. These packages pave the way for mass production of low cost yet reliable green lasers that may eventually substitute for red diode lasers in many consumer-oriented applications.

Diode pumped frequency doubled Nd :YAG microchip lasers should become an alternative to air-cooled argon ion lasers. The main issues to be solved are the long-term stabilization of the single frequency operation and the power control of the multi-frequency operation. These questions are mostly related to the laser dynamics. In this paper, we present an accurate modelling of the laser dynamics, including quenching processes, non uniform pumping, partial overlap of optical signals and excited-state populations, hole burning and type-I frequency doubling. We theoretically predict that even in multimode operation, only one mode is oscillating at a time, with a mode hoping at a rate of about 50 kHz. This behavior, quite different from the well known dynamics of intra-cavity type-II frequency doubled lasers (green noise) is experimentally confirmed. Diode pumped frequency doubled Nd:YAG 473 nm lasers based on a simple linear cavity are built and exhibit high output power (90+ mW) and record slope efficiency (45% with respect to absorbed power). The understanding of its 2-mode operation allowed us to stabilize the average output power. A similar laser was operated on a single frequency. No wavelength drift could be measured and no mode hopping was observed over 24 hours.

Longitudinally diode pumped monolith Nd:YAG laser operating at wavelength 1.34 μm Q-switched by V:YAG saturable absorber was designed. The monolith combine inside undoped YAG crystal, active YAG crystal doped with Nd³⁺ ions and YAG crystal doped with V³⁺ ions as saturable absorber. The pumping radiation is directed through the dichroic resonator mirror to the undoped YAG part which is diffusion bounded to the active Nd:YAG crystal. This configuration ensures the effective heat removal and lower thermal distortion of the active crystal part. V:YAG saturable absorber is diffusion bounded to the un-pumped face of the Nd:YAG section. Thanks to this configuration the effective heat removal from the saturable absorber is accomplished, number of reflecting surfaces and also complete resonator length are reduced. It was proved that this compact monolith system is more stabile, efficient and easy to operate in comparison with classical separated laser configuration.

For years the international laser community has been discussing what the "best" concept for high power solid state lasers might be. With the advent of high power diode lasers of lifetimes in excess of 10,000 hours at long term operational power levels around 50W per diode bar, diode pumped concepts moved into their rightful role as next generation sources. The main reason for this trend is the combination of laser efficiencies in the range of 15 to 25% at powers of several kW with the well known and increasingly applied advantage of fiber coupling. A particularly promising perspective similar to electrical networks is provided by concepts of laser power networks distributing the optical energy on demand in the production environment, especially for large scale production.

We developed the elemental technologies to construct a 1-kW, 10-kHz thin-disk laser. We obtained the wellpolarized CW output of over 900 W without any compensation optics of the birefringence error. The extinction ratio of output was over 1:140. We developed and installed the water-cooled Pockels cell into the CW laser cavity to act as a polarization rotator by applying a DC-voltage to the cell. We confirmed that the cooled cell did not create distinguished birefringence and thermal lensing over 900-W operation. The deforming of thin-disk at high power operation was estimated by using a commercial M² meter. We optimized the cavity configuration from the estimation results to obtain high beam quality. After the optimization, the M² values kept up to 3.5 until the output reached to 400 W. At the 500-W output, the M² in vertical and horizontal plane were 3.65 and 3.02, respectively.

We present the current status of the Lucia laser being built at the LULI laboratory, the national civil facility for intense laser matter interaction in France. This diode pumped laser will deliver a 100 Joules, 10 ns, 10 Hz pulse train from Yb:YAG using 4400 power diode laser bars. We first focus on the amplifier stage by describing the reasons for selecting our extraction architecture. Thermal issues and solutions for both laser and pumping heads are then described. Finally, we emphasize more specifically the need for long-lifetime high-laser-damage-threshold coatings and optics.

We have demonstrated efficient operation of the eyesafe laser transition (⁴I_13/2 -> ⁴I_15/2) in Er:YAG by resonantly pumping with 1470nm diodes. Quasi-cw powers in excess of 30W have been achieved at 10% duty cycle with 47% slope efficiency, 26% conversion efficiency, and beam quality of M²=1.4 x 2.2. In energy storage mode, we have generated near-diffraction-limited 41mJ / 58ns pulses, more than 700kW of peak power, at 10Hz. Storage lifetimes in the range of 5 to 7msec have been measured, and pulses as short as 25ns have been obtained at reduced energy. We believe this to be the first-ever demonstration of a resonantly diode pumped (bulk) erbium laser.

Rare earth doped ternary lead salts are being studied for use as mid-IR laser materials. We summarize progress at the Naval Research Labs on the production and evaluation of this important class of solid-state laser.

For giant pulse generation in the mid-infrared region LiNbO3 crystal with Brewster angle cut faces was inserted inside the Er:YAG laser oscillator and a specially designed driver ensured the precise time of Pockels cell switching. The optimization of the oscillator and Pockels cell driver parameters was performed to obtain the shortest (60 ns) and stable output pulse with maximum energy (60 mJ). It gives 1 MW output peak power. Laser output dependences on the resonator parameters (resonator length and output mirror reflexivity) were also performed and the output laser characteristics well corresponded to the theoretical calculation results.

Spectroscopic and thermo-optic properties of laser crystals are needed for solid-state laser performance modeling. Here we present a brief report on the measurement of key thermo-optic properties: thermal conductivity (κ), coefficient of thermal expansion (α), and thermal coefficient of refractive index (dn/dT). κ was measured using laser-flash method. α was measured using a 632.8-nm He-Ne Michelson laser interferometer. dn/dT was determined at 1064 nm, using measured values of α and the thermal coefficient of the optical path length. An extended paper containing more detailed results will be submitted to the Journal of Applied Physics.

The thermally induced stress of the order of 200 MPa and strain of the order of 2 x 10^-4 in adhesive free bonded (AFB) YAG/sapphire single crystal composites have been determined as functions of crystallographic orientation by stress birefringence measurements using a polariscope and by surface figure measurements using a phase shift Fizeau interferometer, respectively. The deformation of YAG or sapphire end faces of the composite samples into anticlastic surfaces is likely due to thermally induced relative biaxial strain between the YAG and sapphire components during heat-treatment. We have found that the YAG/sapphire composites stay stress- and strain-free when they are heat-treated below a critical temperature. The thermally induced stress and strain increase exponentially with respect to the heat-treat temperature that is above a critical temperature. The magnitudes of thermally induced stress and strain in the heat-treated composite samples allow an estimate of the thermal stress resistance of YAG/sapphire composites. Wright-Patterson Air Force Research Laboratory has supported this work under Phase II Contract F33615-03-C-5442.

In order to develop an efficient eye-safe laser, operating in the 1.53μm region, we have written software that models the performance of a passively Q-switched Er:Yb:glass laser with a divalent cobalt Co²⁺:spinel saturable absorber. At present we have completed a 0D model for which we developed a set of coupled first order differential equations to describe the laser dynamics. These equations represent a two-level Yb³⁺ diode pump scheme, a five-level Er³⁺ gain medium, and a three-level Co²⁺ Q-switch. The model takes into account cooperative upconversion and excited state absorption (ESA) in both the gain and absorber media. Input parameters for the rate equations such as ion concentrations, cross sections, and lifetimes are obtained from experimental and published data. These parameters can be easily varied via a graphical user interface (GUI) that was developed for the model. A study comparing laser characteristics such as pulse energies, peak power, and pulsewidths (FWHM) is carried out between our model and experimental data. Future work will focus on a 1D model which introduces the spatial variation of the pump and laser beam within the cavity.

Dye-laser technology has seen very significant progress over the last 39 years since the first demonstration of this device technology. Dye lasers offer efficient emission in the visible and near-infrared bands by direct generation of laser light. The initial emphasis was on the liquid-phase technology, and is the one very successful liquid laser. More recently the research emphasis has been solid-state versions of this technology and in particular applying diode-laser-pumping techniques to a dye-doped gain medium. In general, dye lasers offer a range of valuable characteristics, as well as significant flexibility, which have been exploited for many applications. Some of these applications are discussed in this paper, along with the fundamentals of dye laser action and its supporting technology.

We present a microcavity solid polymer dye laser based on a single mode planar waveguide. The all-polymer device is self contained in the photo definable polymer SU-8 and may therefore easily be placed on any substrate, and integrated with polymer-based optical or microfluidic systems. As the active medium for the laser we use the commercially available laser dye Rhodamine 6G which is incorporated into the SU-8 polymer matrix. The single mode slab waveguide is formed by a 3-step spin coating deposition: a buffer layer of un-doped SU-8, a core layer of SU-8 doped with Rhodamine, and a cladding layer of un-doped SU-8. The refractive index increases with Rhodamine concentration, and the difference between the un-doped buffer and cladding layers and the doped core layer is fine tuned to 0.001, allowing a large gain volume.

We have demonstrated a laser-pumped, near-infrared solid-state dye laser (SSDL) with a slope efficiency approximately equal to 35%, tunability over approximately equal to 40 nm (from 710 to 750 nm) and M² < 1.3. This device utilizes a folded three-mirror resonator containing a tight focus for the gain medium and a collimated section for the tuning element. The folded cavity is astigmatically compensated through proper choice of sample thickness and cavity fold angle. We achieved low-threshold operation through the tight intracavity focus and by mounting the sample at Brewster’s angle. Two pump lasers were used in this study: (1.) a flashlamp-pumped dye laser (FPDL) with an output wavelength of 630 nm and a pulse duration of approximately equal to 1 microsecond; and (2.) a pulsed red diode laser with an output wavelength of 671 nm and a pulse duration of approximately equal to 200 ns. The gain medium consists of the near-infrared dye Oxazine 725 in the solid host modified PMMA. With the FPDL as the pump source, slope efficiencies up to approximately equal to 35% were measured at the center of the tuning range. A single-plate birefringent filter (BRF) was used to tune the output from approximately equal to 710 to 750 nm with a single output wavelength. The BRF narrowed the spectral output from approximately equal to 15 to approximately equal to 0.8 nm, and provided smooth, continuous tuning over the 40-nm range. Lasing was observed outside this range, but the output consisted of two wavelengths separated by approximately equal to 50 nm (the free spectral range of the BRF). Time-resolved data showed that, for these cases, the laser switches from the shorter to the longer wavelength during the pulse. Input/output curves were generated as a function of resonator feedback for several output wavelengths. Findlay-Clay analyses were used to determine the round-trip cavity loss at each wavelength. The results correlate well with known losses in the resonator, including dye self-absorption losses. Beam-quality measurements were made near the peak of the tuning curve (lambda approximately equal to 727 nm) with a cavity feedback of 95%. At 1.5x threshold, the laser output had an M² value of approximately equal to 1.06. At 7x threshold, the beam quality degraded slightly to M² approximately equal to 1.26. Good temporal tracking was observed between the pump and output pulses, once the SSDL turned on. With design improvements to reduce the threshold, the tunable SSDL was also lased using the diode laser as the pump source. Further characterization of this device under direct diode-pumping is in process.

A number of novel near infrared oxazine laser dyes have been designed, synthesized and purified. The photophysical and lasing properties of these near infrared laser dyes are reported in this paper. The dyes have been found to exhibit moderately high fluorescence quantum efficiencies. Laser testing has been undertaken on the novel oxazine dyes and the results have been compared with those obtained with commercially available near infrared laser dyes.

In this paper we present calculations of the effects on thermal lensing of bonding undoped host crystal to the ends and edges of edge-pumped slab lasers. Using ray tracing and finite element analysis we simulate the distribution of absorbed pump power, 3D temperature, stress, and surface displacements. We numerically calculate the induced lensing due to thermal and stress gradients, and deformation induced end effects. In slabs with undoped material bonded to the edges through which pump light enters, the induced lensing has an "m"-shaped profile while undoped Brewster ends reduce deformation induced lensing.

Design and projected performance of a lightweight, 1064 nm, laser transmitter is described. A 40 mJ, diode side-pumped Nd:YAG zig-zag slab oscillator is configured to operate on either of two Nd:YAG absorption bands (795 nm or 807 nm) to provide stable operation over a 100°C temperature range, using minimal power for diode wavelength stabilization.

Nd:YAG and Nd:YAP slab crystal in the form of triangle with the Brewster-angle-cut polished input faces was used as an active medium for diode-side-pumped laser. A horizontal projection of the active medium form is a triangle with 19.22 mm long base, 5 mm height, and thickness of 4 mm. This active crystal shape is one from the simplest form which makes possible to realise a slab side-pumped configuration with a total internal reflection. Optical pumping was accomplished by a quasi-cw diode ARR18P400 with peak power 400 W closely attached to the active crystal without any coupling optics. Both material were operated for most known Nd³⁺ ion transition ⁴F_3/2→⁴I_11/2 (1 μm) as well as for transition ⁴F_3/2→⁴I_13/2 which leads to the emission at 1.3 μm. The systems were tested in free running and Q switch regime. This system is enough compact to be useful tools for direct medical application.

A novel Nd:YAG micro slab laser amplifier is presented and experimental results for Q-switched operation are discussed. The laser crystals are directly pumped by conduction cooled laser diodes with an ISO/FDIS 17526 extrapolated standard lifetime above 30,000 h. The diffraction limited cw output power of the amplifier is 50 W. In pulsed operation, the laser shows a pulse energy of 4.65 mJ and a pulse length of 12 ns FWHM at a pulse repetition rate of 6 kHz. Beam quality has been measured to be M² = 1.1. The beam pointing stability was 10 μrad and the pulse-to-pulse stability was 1.5% rms in a linear-polarised beam.

In this paper, we will present recent results from the first commercially available rotary disk laser. Rotary disk laser concept introduces physical motion as a new control element in solid state laser designs. Rotary disk lasers have the potential of producing much higher power in single-mode operation than other types of bulk solid state lasers. Rotary disk lasers also have the potential of generating much higher energy pulses than fiber lasers. The Nd-YAG rotary disk laser produced 30.8 W of output power in a single mode at 32.4% optical efficiency. In a preliminary test, 81.9 W was obtained from a single mode Yb-YAG rotary disk laser.

A technique of direct writing of depressed cladding waveguides by a tightly focused, femtosecond laser beam in laser crystals has been developed. A laser based on a depressed cladding waveguide in a Neodimium doped YAG crystal has been demonstrated for the first time.

Initial experiments with pulsed and CW pumping an alexandrite laser rod at 532 nm are presented. This pumping architecture holds promise for the production of scalable diode-pumped, tunable alexandrite laser systems operating in the near infrared (750 nm), and the ultraviolet (375 and 250 nm) spectral regions.

Since its introduction the thin disk laser based on Yb:YAG material has been thoroughly investigated and first industrial systems are now available. Nevertheless, some problems arise when scaling the power up: The pump set-up is becoming complicated and there could be some difficulties in bonding the thin disk on the cooling finger. In this paper, we describe a novel pumping scheme solving those two problems. Instead of pumping from one face or on the side of thin disk we propose to use a combination of both using an additional optical element to guide the pump light to the disk. We show that up to 85 % of pump light can be absorbed by the laser material and the pump distribution can be very homogeneous. FEA calculations show that this configuration is also favourable to a better cooling of disk and reduced deformation in the laser material.

Single-frequency IR and visible lasers are of a great interest in many research and application fields. We present in this paper, what we believe to be, to the best of our knowledge, the first diode-pumped Ytterbium-doped solid-state laser emitting at 1003.4 nm in single-frequency operation and first results obtained in the blue-green region by second harmonic generation (SHG). The laser is based on an diode-pumped Yb:YSO (Yb:Y₂SiO₅) crystal. The choice of an Yb-doped crystal, pumped at 978 nm, involves two main constraints. First, the small difference, between pump and laser wavelengths, prevents the use of suitable standard dichroic mirrors. Secondly, due to the quasi-three level transition, reabsorption is significant around 1 μm and pump-absorption has to be highly saturated all along the crystal length. The pump source is a single-emitter laser diode providing a maximum power of 4 W at 978 nm. The resonator is a six-mirror ring-cavity containing a Faraday rotator to obtain unidirectional operation. A thin Fabry-Perot etalon at Brewster angle is used to maintain linear polarization as well as finely tune the laser wavelength. More than 300 mW of single-frequency radiation at 1003.4 nm has been obtained for 3.2 W of incident pump power. First intracavity SHG results are also presented using a KNbO₃ nonlinear crystal at 76.5 °C to operate in non-critical phase-matching. In this configuration, 300 mW of IR radiation and 14 mW of aquamarine wavelength (501.7 nm) have simultaneously been obtained at room temperature in single-frequency operation.

Results of experimental investigation of diode pumped Nd:YAG laser passively mode locked using either second harmonic nonlinear mirror or semiconductor saturable absorber are reported. As an active element the 10 mm long Nd:YAG rod end pumped by 20 W fiber coupled laser diode was used. The linear folded resonator has on the other end either saturable absorber with single 15 nm thick In 0.25 Ga 0.75 As quantum well layer integrated on the top of Bragg mirror (SESAM) either nonlinear mirror (NLM) consisting of a dichroic dielectric mirror and crystal for second harmonic generation (SHG). With SESAM the 2.5 W of average output power and pulse duration of 21 ps was achieved, using the 3.5 mm long type II KTP crystal we obtained 1.5 W of output power with single pulse duration of 26 ps. Substantial pulse shortening to 9 ps was achieved with a 10 mm long critically phase-matched type I LBO crystal.

Gain-switching of laser diodes might be the most convenient way to generate picosecond laser pulses. The outstanding features of gain-switched laser diodes are a rich choice of wavelength and an easy synchronization to an external trigger source. To broaden the field of applications we pushed the peak power to the 10 W level while maintaining the essential characteristics of the laser source. In a master oscillator power amplifier (MOPA) configuration a tapered amplifier is used to increase the output from 10 mW to 160 mW average power. Second harmonic generation is demonstrated in a single pass setup, which results in 6.5 mW average power at 532 nm with a repetition rate of 80 MHz.

Multimode optical fibers are used for the transmission of high power laser pulses and as phase conjugated mirrors by stimulated Brillouin scattering. Both applications are enhanced by antireflection coatings on the fiber end-faces. Fiber transmissions reach more than 99.5% for pulse energies below the threshold of stimulated Brillouin scattering. Laser-induced damage thresholds of the fibers coated with Ta₂O₅ / SiO₂ were measured at 1064 nm and 24 ns pulse duration. A damage threshold of up to 101 J/cm² could be achieved. The damage morphology was investigated using atomic force microscopy and scanning electron microscopy.

Passive Q-switch modulators of plastic dye sheets ( Kodak 9850 cellulose acetate dye sheets), lithium fluoride crystals containing F₂- color center ( LiF: F₂^-), chromium doped yttrium aluminum garnet crystals (Cr⁴⁺:YAG), ionic color filter glass (Schott RG1000 color filter glass) and the single crystal semiconductor wafers (GaAs, Fe doped InP, Zn doped InP, S doped InP, etc.) have been investigated in our research. Especially in use those of the single crystal semiconductor wafer saturable absorbers, give us idea of developing the semiconductor substrate microchip lasers.

All solid state mode-locked flashlamp pumped Nd:YAG laser system with selectable pulse duration was developed based on the oscillator where a single semiconductor structure containing a multiple-quantum-well was used as a saturable absorber for mode-locking, and energy limiter for passive negative feedback. Single pulse selection from various parts of extended 200 ns long Q-switched pulse train enables the changing of pulse duration before entering into three stages of laser amplifiers. Using of additional acousto-optic mode-locker, stability enhancement of the output pulses was obtained and the amplitude fluctuations were reduced below 5%. The exploitation of the solid state saturable absorber and limiter integrated in the single element improved significantly the long term characteristics of the laser system which can be therefore used for various applications as a satellite laser ranging, spectroscopy, or medicine.

A pulse-train Nd:YAG laser system consisting of repetitively Q-switched Nd:YAG oscillator with Cr⁴⁺:YAG saturable absorber, double pass Nd:YAG amplifier and stimulated Brillouin scattering (SBS) pulse compressor has been demonstrated. Number and energy of the laser pulses were controlled by adjusting width and amplitude of the flash lamp pumping pulses. Efficient SBS compression of Nd:YAG laser pulses was obtained using single-cell compressor.

The function of laser fuzes which are parts of certain weapon systems is to control the blasting height of warheads. Commonly the battle environment these weapon systems are confronted with is very complicated and the tactical demand for them is very rigor, so laser fuzes equipped for them must fulfill some special technical requirements, such as high repetition rate, long ranging scope, etc. Lasers are one of key components which constitute fuze systems. Whether designed lasers are advanced and reasonable will determine whether laser fuzes can be applied in these weapon systems or not. So we adopt the novel technology of diode-pumped solid-state laser (DPSSL) to design lasers applied in fuzes. Nd:YVO4 crystal is accepted as gain material, which has wide absorption band and large absorption efficient for 808nm pumping laser. As warhead's temperature is usually very high, wider absorption band is beneficial to reduce the influence of temperature fluctuation. Passive Q-switching with Cr⁴⁺:YAG is used to reduce the power consumption farthest. Design the end-pumped microchip sandwich-architecture to decrease lasers' size and increase the reliability, further it's advantageous to produce short pulses and increase peak power of lasers. The designed DPSSL features small size and weight, high repetition rate and peak power, robustness, etc. The repetition rate is expected to reach 1 kHz; peak power will exceed 300 kW; pulse width is only 5 ns; and divergence angle of laser beams is less than 5 mrad. So DPSSL is suitable for laser fuzes as an emitter.

It is very difficult to achieve both high-power and low divergence lasing at once in cw or high-repetition rate lasers because thermal effects limit their efficiency. But as these effects are stable over time, a passive correction is conceivable. In this paper we propose a very simple but effective method to compensate the thermal effects in such lasers, using an aspherical phase-plate inside the resonator. The first results are very promising, as we demonstrated a very stable 418 W, M²=5.7 laser for only 2280 W of total optical pumping power (i.e 2050 W of absorbed pump power).

We report on direct, absolute and spatially resolved temperature measurements in various diode-end-pumped laser crystals, using an infrared camera. Our measurement method requires careful calibrations of the camera, to take into account the emissivity of the crystals. We tested the repeatability of the calibration process, and the linearity of calibrations curves was verified to up to 100°C. We obtained good agreement between experimental results and finite elements analysis simulations done with LASCAD. We also studied and compared different types of thermal contacts and to measure the corresponding heat transfer coefficients using an Yb:YAG crystal. Finally we tried to highlight one of the major controversy concerning the comparison of the thermal behaviours of Nd:YVO₄ and Nd:GdVO₄ crystals.

LIBS is one of the best methods of multilayer coatings studying. Special laser technique-scanning sampling-was developed for studying of different kinds of objects (technical and biomedical coatings). The scanning sampling is based on the scanning of analyzed object during the exposition time. The velocity of scanning is defined by the diameter of laser crater and pulse repetition rate. It allows to increase the volume part of a coating substance in a sample. Some special applications of LIBS and scanning sampling with Q-switched Nd:YAG-laser in the field of technics and biomedicine are described. The layer-by-layer elemental analysis of multilayer components was performed for finding-out the probable non-uniformity. That could appear the reason of wrong work of components. Special layer characteristic calculated as a ratio of spectral lines intensities for elements contained in different layers of a coating was defined for estimation non-uniformity. LIBS in investigation of dental tissues allows to define preliminary the nature of pathology. Scanning sampling used for such tissues as debris and odontolith, allows to find out the stage of lesion and to predict carious conditions.

Air can be considered as a nonlinear optical medium for sufficiently high laser intensities. Short pulses of high peak intensity have been seen to create their own waveguide and propagate through the atmosphere while maintaining a diameter of the order of 100 μm over distances far in excess of the Rayleigh range. It is generally believed that the waveguiding results from a balance between self-focusing (Kerr effect) and self-defocusing due to a low desnity electron plasma created by multiphoton ionization of air. This delicate balance is destroyed after a short time because of inverse Bremstrahlung, which leads generally to avalanche ionization. Observation of filaments has therefore been limited to femtosecond pulses. At wavelengths shorter than 306 nm, ionization of oxygen is only a 3 photon process, and therefore the intensity in UV filaments is 20 to 3 orders of magnitude smaller than in the IR. Furthermore, the time required for inverse Bremstrahlung to lead to avalanche ionization is 1000 times longer, i.e. of the order of a nanosecond. As a consequence, it should be possible to channel up to 1 Joule of energy in the UV filaments, as opposed to a few mJ. To create such high energy, we have developed a compact frequency quadrupled Nd:YAG laser oscillator-amplifier, compressed from 3 ns down to 200 ps by stimulated Brillouin scattering in FC75. The oscillator is seeded by a stabilized semiconductor laser to ensure the narrow band operation required for the stimulated Brillouin scattering. Efficient transfer of power from the beam to the filaments is achieved by focusing the larger beam issued from the Brillouin cell in vacuum, onto a supersonic flow of air serving of window between vacuum and atmosphere.

Various solid state lasers such as Cr:LISAF, Yb:YAG, Nd:Vanadate, Ti:sapphire and Nd:YAG have in common a long lifetime of the laser level, which results in a tendency to Q-switching rather than pure mode-locking. These lasers are being used in a linear or ring cavity for intracavity sensing applications (displacements, rotation, electric and magnetic fields), and for applications in spectroscopy. The requirements for these applications are that the pulses be centered at a specific wavelength, and be of a specific pulse duration. Multiple Quantum Wells (MQW) typically used for ultrashort pulse generation have often a high defect concentration which causes losses incompatible with the large number of intracavity elements required by the applications. We have established for all these lasers a composition curve for the MQW, that enables one to tune to a specific wavelength. These saturable absorbers have excellent optical quality both in reflection and transmission. The approach to prevent Q-switching has generally been to use very low loss modulation (single quantum wells). With a large number of intracavity elements, a larger loss modulation is desirable, hence the use of multiple QW (4 to 100). We have successfully demonstrated stable continuous model-locked operation by using passive energy limiters in the cavity. Two-photon generated carriers induce lensing in the cavity, resulting in power dependent losses through an aperture in the cavity. We show that the attenuation is proportional to the square of pulse intensity, resulting in a steep energy limiter. We demonstrate theoretically and experimentally that the presence of two intracavity pulses required for sensor applications can be satisfied with multiple quantum wells appropriately positioned in the cavity. Examples of applications include rotation sensors (ring cavity) or acceleration sensors (linear cavity), magnetic filed sensor, displacement sensors.

In this paper, we report a diode-pumped passively Q-switched Yb:YAG laser that is an excellent candidate for a ladar master oscillator. This microchip laser has 1 ns pulse duration, 68 μJ pulse energy, 700 mW average power, 10 kHz repetition rate, and 29% optical slope efficiency. Additionally, the microchip oscillates in the fundamental TEM₀₀ mode. The peak power was measured as high as 66 kW. We compare the pulse shape and duration, and the beam quality to simulation. We study the effects of Q-switch absorption, output coupler reflectivity, cavity length, and pump power on the laser's pulse duration, pulse energy, average power, and repetition rate.

Fiber laser pumped Er:YAG laser action at 1617 nm was achieved at room temperature. An etalon was utilized for tuning the laser to the 1617 nm line. Room temperature operation was characterized and compared with 1645 nm operation. Output power close to 3 Watts CW was demonstrated at the 1617 nm laser line.

1534 nm Fiber laser pumped Er:YAG laser action at room temperature has been demonstrated with high efficiency. CW power as high as 12 Watts was achieved at 1645 nm from Er:YAG where a single TEC controller was used for thermal management. Active EO Q-switched operation with kHz repetition rate and 27 ns pulse widths was achieved with the same laser resonator.

We developed a computer model for simulating real solid state laser systems, by solving the paraxial wave Eq.s in the multi-physics modeling software FEMLAB. The reflection of the laser on the curved cavity mirror is calculated by an analytical method. This model was verified to be able to give very accurate results, by applying it to empty stable and unstable resonators, and a face pumped Yb:YAG disk stable resonator laser.

The Department of Defense (DoD) Militarily Critical Technologies Program (MCTP) provides a systematic, ongoing assessment and analysis of goods and technologies to determine those that would permit significant advances in the development, production and use of military capabilities of potential adversaries and those that are being developed worldwide that have the potential to significantly enhance or degrade US military capabilities in the future. The program's objective is to characterize the technologies, including quantitative values and parameters, and assess worldwide technology capabilities. The MCTP is composed of two sets of documents, the well known and often referenced one, the MCTL, and a second one, a more recently added list called the Developing Science and Technologies List (DSTL). Both are products of the MCTP process, however, the later is primarily used by DDR&E and other government organizations and agencies to aid in the prioritization and understanding of new technologies being developed worldwide. Technologies are selected for the MCTL and the DSTL through the deliberation and consensus of Technology Working Groups (TWGs). TWGs continually screen technologies and nominate items to be added or removed from the MCTL and the DSTL as appropriate. Working within an informal structure, TWG members are composed of government, industry and academia subject matter experts, who strive to produce precise and objective analyses across each technology areas. This process and details of the current MCTP are outlined in this poster paper. This paper focuses on the solid state laser technology area, using it as an example of the MCTP's product of assessing, identifying, and quantifying militarily critical technology parameters.

A CW Na guidestar excitation source has been constructed and installed on the 3.5-m telescope at the Starfire Optical Range. This device is comprised of injection-locked Nd:YAG ring lasers operating at 1064 nm and 1319 nm and a doubly resonant cavity where sum-frequency generation of these wavelengths in LBO produces a diffraction-limited linearly-polarized 589-nm beam. Up to 50 W of 589-nm light for mesospheric guide-star generation has been produced. The injection-locked Nd:YAG lasers are capable of operating at up to 100 watts at 1064 nm and 60 watts at 1319 nm.

The development of an alumina-rich cobalt-doped spinel saturable absorber for the passive q-switching of 1530-1555 nm lasing is reported1. This optimized composition results in crystals with excellent dopant uniformity that are highly manufacturable. The crystal growth and materials characterization are described as well as initial passive qswitch testing of the material. The single crystals grown and investigated crystallized in the Fd3m space group and have the formula Mg_1-xCo_xAl_yO_z where x is greater than 0 and less than 1, y is greater than 2 and less than about 8, and z is between about 4 and 13. Comparison data of stoichiometric spinel MgAl₂O₄ and alumina-rich non-stoichiometric spinel MgAl₆O₁₀ are presented. The spinel lattice is comprised of octahedral and tetrahedral cationic sites, and in the alumina-rich spinel essentially all of the magnesium and cobalt occupy tetrahedral sites. The alumina-rich cobalt-doped spinel studied exhibited uniform cobalt-dopant distribution throughout the crystal and desirable mechanical and physical properties. Q-switched pulses were produced using the alumina-rich Co²⁺:MgAl₆O₁₀ saturable absorber in a 980 nm diode-pumped Yb:Er:glass solid-state-laser operating at 1543 nm. The q-switching established employed the ⁴T₁ absorption band of the Co²⁺: MgAl₆O₁₀ and with quasi-CW pumping, pulsewidths greater than 20 ns, pulse energies of greater than 250 mJ, and free-running pulse repetition frequencies (PRFs) up to 1.2 kHz were demonstrated.