The current performance of the high average power CHIRP II excimer laser is described. A power of 430 W at 1100 pps has been achieved on the XeCl excimer. Particular reference is made to the undesirable high pulse repetition frequency (PRF) effects observed in the testbed CHIRP I laser, and successfully avoided in CHIRP II.

A fast risetime, 2 kHz, long-lifetime x-ray preionizer has been developed. The device is intrinsically rugged and simple and a lifetime of 2.5 X 10⁸ shots has been demonstrated with an estimated potential lifetime in excess of 10⁹ shots. The system is based around a highly evolved form of corona plasma (surface discharge) cathode. The life- limiting factors of this type of cathode were identified and overcome in the course of the development program. The device operates at approximately 95 kV and is capable of creating preionization electron densities of > 10⁷ cm^-3 in 1 atm. of Ne after the x rays have traveled 4 - 5 cm and passed through 1 mm of steel and 2 mm of aluminum. Beam uniformity and reproducibility are maintained at 2 kHz. Very homogenous glow discharges at repetition rates up to 1.5 kHz have been obtained in a prototype industrial grade XeCl laser incorporating such a preionizer.

The first 1 kW laser was achieved by SOPRA in August 1992 with high energy per shot (i.e., 10 J X 100 Hz and 13 J X 80 Hz) in short burst mode (typically 1 sec to 10 sec). After this result the SOPRA team focused its work in two directions: (1) Longer burst (typically 1.5 hour) in order to attend thermal equilibrium of the set-up for lower pulse repetition frequency (PRF); and (2) specific applications beam adapting. However most of the customers' applications at the present time require high energy per pulse at low PRF but keep in mind that the laser will be able to work at higher frequency in the near future. So work has been done on the beam shape quality: it is reproductive. It can be either homogeneous in the near field or, with low divergence for far field. Application surface is much larger than with conventional excimer laser or creates an affect not possible with conventional excimer laser.

The progress of the development of an 1 kW, 1 kHz XeCl laser is reported. The laser consists of a low loss gas circulation system, a corona-plasma cathode x-ray pre-ionizer, and a pre- pulse main-pulse excitation circuit generating long optical pulses. The performances of the pre-ionizer and the electrical circuit are described.

We have developed high repetition rate, high average power excimer lasers intended for industrial applications. They operate in the phototriggered mode and have a compact design. The first prototype has been proven to operate continuously up to 700 Hz and delivers more than 500 W average power. A second prototype is intended to work at the same repetition rate. It delivers up to 2 J output energy at low repetition rate.

In this paper, we are reporting for the first time on a spiker-sustainer XeCl laser operating at a PRF of up to 1 kHz. The laser is x-ray pre-ionized in the interest of pre-ionization homogeneity and in order to avoid contamination of the laser gas. A conventional flow loop was employed, having a maximum flow speed of 50 m/s at 3 bar, which translates into a clearing ratio of 2.5 at a PRF of 1 kHz. A pyroelectric energymeter (GenTec ED500) was used to measure single-shot energies. The pulse energy in repetitive mode and the pulse duration were observed with a calibrated vacuum photodiode. The spatial beam profile was recorded on photosensitive Dylux paper. Among the different spiker modes tested, a modification of the overshoot mode gave the best results in terms of efficiency, output energy, and overall laser stability.

Annular gain media offer various advantages to the design of lasers. The advantages comprise efficient laser excitation by internal pumping sources for solid state lasers and large discharge surfaces for diffusion-cooling of high power CO₂-lasers. To benefit from these advantages it is necessary to find a suitable resonator. The presented solution to the resonator problem consists of a hybrid resonator which is stable in radial and unstable in azimuthal direction. Basically, it can be considered as the annular equivalent of the well-known stable-unstable slab resonator. A geometrical model of the resonator indicates that for proper resonator function the mirror shapes must respect certain constraints. A diffraction model of the loaded resonator gives detailed information on the beam properties and extraction efficiencies. To reduce the computational effort for beam propagation an approximate diffraction kernel for annular beams has been used. Experimental data on a 1 kW diffusion-cooled CO₂-laser are reported.

Diamond turning techniques for high power laser optics were developed during the 70s and 80s as the alternative to conventional polishing of optical surfaces. In principle there are two main areas of applications for diamond tooled high power CO₂ laser optics: (1) Aspheric transmissive ZnSe-/Ge-lenses for focussing at very short focal lengths or parabolic Cu- surfaces for laser welding heads. (2) Cu-surfaces for use as extracavity and intracavity beam bending mirrors. In this presentation we concentrate on item two.

A computer simulation is carried out in order to analyze elementary processes in the active medium of a supersonic electro-ionized CO laser operating with Ar-CO and Ar-CO-O₂ gas mixtures. The calculations are based on a homogeneous discharge model. The aim of the work is to study the influence of the ion-molecular and plasma chemical reactions in the laser discharge on ionic and chemical composition of plasma.

For the development of compact high-power CO₂ lasers high input power densities in discharge tubes with sufficiently large cross sections are required. To achieve a uniform distribution of power deposition into the laser gas flowing in tubes with typically circular cross sections an appropriate electrode shaping is necessary. For this reason, experimental and theoretical investigations have been performed in a wide range of input power, starting from values typical for todays CO₂ lasers up to very high levels. Different electrode shapes have been used for optimized stability and homogeneity of the discharge in order to minimize the distortion of the intra-cavity wavefront. The occurrence of filaments limits the range of a stable discharge operation. The homogeneity of the discharge has been assessed by means of spatially resolved small signal gain measurements. Further, the homogeneity of the discharge as a prerequisite for minimal phase distortion has been investigated using an interferometer. A discharge with 17 kW input power at 13.56 MHz in a single tube element is presented showing a flat profile of the small signal gain and a phase distortion of 0.21 micrometers .

CO₂ slab waveguide lasers have gain regions defined by two rectangular, flat electrodes, which are typically separated by approximately 2 mm. These electrode surfaces act to both excite the laser gas and to guide the laser light in a plane perpendicular to the surfaces. The component of the light propagating parallel to the electrode surfaces is acted on only by the resonator mirrors, and hence the complete laser is therefore a hybrid conventional/waveguide laser. These lasers share many of the properties of pure waveguide lasers, including mode selection, coupling losses, etc. It has been observed that CO₂ slab waveguide lasers can exhibit erratic mode/wavelength shifts when broadband optics and non-optimized waveguide structures are used. An improved laser resonator is presented that operates on a single vibrational transition of the CO₂ molecule by simultaneously optimizing the waveguide mode losses and by employing wavelength selective optics.

We report on the development of a 260 mJ 248 nm KrF laser with 98.7% depth of modulation at 1.3 GHz and 77% depth of modulation at 2.6 GHz using a 1.3 GHz microwave source driving a Pockel's cell. Subsequent single-pass amplification of the modulated KrF source to the 1/4-joule level is shown to be straight forward with no noticeable degradation of the modulation depth.

Magnetic-spiker electrical circuits for gas discharge lasers are described. A new modified overshoot mode of magnetic-spiker XeCl laser excitation is presented as a possible circuit for high repetition rate operation. PSPICE computer simulations of a number of magnetic-spiker XeCl laser circuits are compared with experimental results.

A novel discharge configuration has been realized with the XeCl laser IANUS, which has been developed at the ENEA Frascati center as a 1:1 laser head prototype for the 1 kW average output power XeCl system EOLUS (EUREKA EU211 Project). The patented design of the discharge region consists of two active zones which are geometrically in parallel and electrically in series. The obvious advantages of this configuration are, the presence of the intermediate high impedance electrode, suitable for prepulse application, then the absence of current return bars, so improving the recirculating gas flow uniformity, and the automatic synchronization of the two discharges very useful for a compact oscillator-amplifier configuration (POPA). A number of measurements have been done on IANUS, to have an almost complete characterization; based on these results a generalized self-filtering unstable resonator (GSFUR) has been designed and realized on the smaller gap, leaving the other active medium for the high optical quality beam amplification, in the scheme of a POPA system. The GSFUR output beam results are 1.5 times the diffraction limit, with an energy of 9 mJ in a 87 ns FWHM pulse.

Two high-power CO laser installations for industrial applications are being developed now in Russia within the framework of the Eureka Project EU113 (`CO-Eurolaser'). The electron- beam-controlled-discharge (EBCD) method for pumping those lasers is used. The first one, EBCD 10 kW CO laser, operates in continuous wave and `gentle' repetitively pulsed (RP) (peak power 20 kW, laser pulse duration 0.5 - 1 ms, pulse repetition rate 500 - 1,000 Hz) modes. The second laser, EBCD 5 - 10 kW CO laser will operate in `tough' RP mode (peak power 0.2 - 1.0 MW, single pulse energy 100 J, pulse duration 0.1 - 0.5 ms, repetition rate 50 - 100 Hz). A detander-compressor device, the main characteristics of which are reported, will be used for cooling the laser mixture of the second CO laser. Those high-power CO laser installations are supposed to be used for investigation of different laser materials processing methods on 5 micrometers wavelength for deep penetration welding, cutting, and surface treatment and also for comparative materials processing studies on CO and CO₂ laser wavelengths.

On our way to industrial high power lasers up to 40 kW, we have successfully realized the first step, i.e., the development of an extremely compact 12 kW CO₂ laser with a very high beam quality. The laser is capable of high frequency pulsing up to 100 kHz with consistent mode quality over the full power range from 5 - 100%. Detailed beam quality analysis is presented. In its 10 kW version, this laser has a beam quality better than K equals 0.35. This unmatched focusability permits high quality deep penetration welding and ultra high power cutting applications. Current work concentrates on a completely new 20 - 30 kW laser, which should show similar characteristics as the 12 kW laser with regard to spatial and temporal beam quality. Furthermore, with the foot-print of the laser head being only 4.5 m², this system is significantly smaller than those that are currently available, which is a prime consideration for expanded industrial use.

A new series of fast axial flow CO₂ lasers in the power range from 10 kW to 20 kW for applications in industrial production was introduced into the market in 1993. Five different lasers are available equipped with stable or unstable resonator configurations. They deliver a nominal and guaranteed power of 10 kW, 12 kW, 15 kW, 17 kW, and 20 kW. In the following an overview of the techniques used, the technical performance, and typical application data are presented.

Increasing the output power of fast axial flow high power CO₂ lasers requires a proportional growth of mass flow with the laser power for convective cooling of the active laser medium. Besides the demand on increasing output power the demand on small laser beam sources enforces the integration of all laser components in a tight assembly. By using compact turbo blowers it is possible to maintain a large mass flow with small and lightweight blowers within a compact beam source. In addition to experimental work a program for the simulation of closed gas circuits is presented as a tool for analysis and optimization. The structure of a typical flow system and its transfer to the program is presented. Results of calculations on closed loop flow systems and on open flow systems are presented. Varying basic parameters provides estimations on the overall performance of a modified laser system. With a similar approach applied to an open flow system requirements on central components can be listed.

The paper presents the results on investigations and development of multichannel CO₂ lasers with diffusion cooling of active medium excited by discharge of audio-frequency alternating current. Various methods of improving the laser beam quality and energy efficiency have been considered and experimentally tested.

Sealed-off, metal-ceramic pseudospark switches are currently being developed as a replacement for conventional thyratrons in pulsed gas discharge lasers. In this contribution the performance of different type of pseudospark switches at different load conditions typical for pulsed gas discharge lasers is discussed. Experiments were performed at a low inductive 1 (Omega) water pulse line at holdoff voltages of up to 32 kV with a dI/dt of 6 X 10¹¹ A/s (10% - 90%) and a maximum current of 30 kA. Switch parameters were continuously recorded at repetition rates of up to 100 Hz. In a second experiment the long-term behavior of a pseudospark switch in an excimer laser test circuit was investigated. At a repetition rate of 233 Hz and a charging voltage of 22 kV a nearly unipolar current pulse of about 10 kA in amplitude with a length of 170 ns (FWHM) was obtained. Again switch parameters were on- line recorded. Further the power loss to the electrodes could be determined. Performance of those type of pseudospark switches and the application in real laser systems are discussed.

Efficient low voltage operation of a XeCl laser has been achieved setting a reverse-bias unit on the discharge gap of a system working in the auto-prepulse (AP) mode. Efficiencies up to 1.7% with this improved device even at a charging voltage as low as 7 kV for the main storage unit and for the bias are reported. Experimental results are presented and discussed.

The results of experiments on four-wave interaction of electron-beam-controlled discharge (EBCD) pulsed CO₂- and CO- lasers' radiation inside their active medium are presented. Linearly polarized probe CO₂ (CO-) laser beam intersects strong electromagnetic waves counterpropagating through an inverted medium inside the laser resonator. The laser beam reflected from the active medium has been registered both in near-field zone and in far field. The experiments on recovering of optical images in near-field zone and recovering of angular divergency of laser radiation in far-field zone demonstrate that the reflected beam was a phase- conjugated one. The reflectivity of the phase-conjugated beam was up to 2% for CO₂- laser and up to 0.2% for CO- laser. The time-history of phase-conjugation reflectivity and comparison with theoretical results are discussed.

A kinetic model constructed previously is used to describe the pulse passage through the amplifiers and other elements of the iodine photodissociation laser system PERUN. The results of numerical code including the values of pulse energy after each of the four system amplifiers may serve for an optimization of the system performance and its modifications to fit the demands of target experiments.

In this work the method of statistical simulation allowing someone to calculate an interaction of laser pulse with nonlinear absorbing many-level medium when the time duration of pulse is equal to longitudinal characteristic relaxation time is suggested and realized. Two problems were solved by this method. The first problem was the one of laser energy storage on the metastable level of medium atoms. The space and time characteristics of this inverted medium of plane geometry were calculated. The amplification coefficient of forbidden transition versus different parameters of this problem was obtained. The second problem was the calculation of many-steps selective photoionization of the atomic beam. Under specific conditions a superradiance had an effect on output of ions during decay of resonant exciting level into metastable level.

A theoretical model has been developed to study the XeCl phototriggered lasers developed in the frame of the Eureka EU205 program: one of small active volume studied at LPGP, and a larger one at LASERDOT. Over a large range of experimental parameters, a pretty good agreement is obtained for the evolution of the electric parameters and the laser output characteristics -- energy and power. At moderate pressures (2 - 3 bars), and high energy loading (400 - 600 J/l), the temporal evolution of the laser power exhibits the successive emission of several laser pulses. This feature is also predicted by the model, but the calculations largely overestimate the energy included in the later pulses. The physical reasons for this disagreement have been established on the LPGP device, for which optical spectroscopic studies have shown the development of discharge instabilities.

The tantalum and titanium plates were treated by pulsed, high power CO₂ laser in the pressurized atmospheres of N₂ and O₂. Studies performed by the optical microscopy, microhardness measurements, and the auger electron spectroscopy revealed: (1) topographic modification of the surface caused by the temperature field; (2) metal hardening, caused by the laser shock; and (3) alloying/cladding, caused by the chemical reaction between the metal surface and the gaseous atmosphere.

This article reports on a long pulse excimer laser with autopreionization. Laser pulses with energy of 140 mJ and duration of 180 ns were generated using a discharge circuit built on the basis of main and peaking capacitors driven by a thyratron. Pulse duration of 250 ns and single frequency generation were achieved.

The results of investigation of injection-locked KrF laser Raman conversion in deuterium are presented. Photon conversion efficiencies of 23% to the second Stokes order and of 27% to the third Stokes order at deuterium pressure of 35 atm are obtained. The described excimer- Raman laser system may be used for the ozone sounding in stratosphere and troposphere.

The characteristics and potential applications of high power pulsed electron beam controlled discharge (EBCD) N₂O laser are discussed. The influence of pressure, temperature, composition, and components' ratio of laser mixture on the discharge properties, laser gain, and lasing parameters have been studied experimentally. The small signal gain measurements and N₂O laser wavelength tuning were carried out for P- and R- branches of N₂O molecule from P(2) to P(46) and from R(47) to R(2), respectively. The maximum specific output energies were 40 J/l atm (efficiency approximately 10%, free running laser mode), 16 J/l atm (P-branch line P(18), single line selective laser mode), and 12 J/l atm (R-branch line R(20), single line selective laser mode). The relaxation constant of N₂O laser levels and the excitation efficiency in EBCD are estimated.

The concept and results of R&D of high power (up to 10 kW and more) industrial cw CO₂ lasers are presented. Dc-excited fast transverse flow lasers and ac-excited diffusion cooled multi-channel lasers are investigated, developed, and manufactured. These lasers have improved beam quality (divergence -- less than 0.8 mr), reliability, and maintenance. New laser models of modular generator-amplifier scheme are under development.

Iodine laser produced plasma was characterized and used to test linearity of responses of different soft x-ray detectors.

An electric-discharge-pumped XeCl laser using phototriggering by x rays is described. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a 4-l active volume with an efficiency of about 2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A uniformity analysis of the discharge pumping has been made for the XeCl laser.

The spectral, temporal, and spatial influence of a dye-laser-induced preionization for XeCl discharge-pumped lasers has been measured. Positive or negative response of amplified spontaneous emission (ASE) in the laser active medium on an additional preionization is dependent on the pumping power density and HCl concentration. Mechanisms of additional free electrons creation and decay have been discussed for VIS and UV pulsed preionization.

The results of gas lifetime experiments in ArF and KrF avalanche discharge lasers utilizing different laser chamber materials are presented. Utilization of aluminum ceramics protecting laser chamber polymeric walls from UV gas discharge radiation give us the possibility to increase significantly gas lifetime. Two different physical mechanisms restricting gas lifetime were considered. The first one is connected with interaction between fluoride and organic molecules. The second one (unremovable in avalanche discharge lasers) is connected with electrode erosion processes. The numerical evaluations of the gas lifetime limitation value in ArF and KrF lasers are presented. The different ways of further increasing gas lifetime are discussed.

An analytical technique based on a generalization of the Stappaerts method is proposed for discharge electrode designing. It allows one to consider asymmetry elements, such as current return bars, or to approach new laser geometries, e.g., the double-head laser.

Solid-state laser and x-ray laser research activities at the Institute for Solid State Physics of the University of Tokyo are reviewed. A description of the four-beam multi-TW neodymium- doped phosphate glass (Nd:Glass) laser system is given. Advanced laser research, such as the development of a table-top ultra-short pulse TW Nd:Glass system and phase conjugate system, are also reviewed. Studies on recombination pumped soft x-ray lasers with He-like ions are presently underway. Picosecond x-ray spectroscopy of laser produced aluminum plasmas revealed population inversions between the n equals 3 - 2 levels of He-like Al ions. Details on the first observation of amplification in a recombination pumped He-like soft x-ray laser, showing a time-resolved small-signal gain of 3 cm^-1 for the 3¹D - 2¹P transition of He-like N, are also given.

In this talk the affects that determine the beam quality of high power Nd:YAG lasers are discussed. Suggestions are made on how the beam quality can be improved. Experimental results concerning the relationship of output power and beam quality are presented. The different sources of thermo-optical aberrations in rod and slab lasers that influence the beam quality of stable resonators are discussed. Design criteria for rod and slab lasers with improved beam quality are presented and the direction of future work is outlined.

A high average output power of a solid state laser is achieved by means of a temporal multiplexing method. It combines several laser beams and conserves the beam quality of each beam in the combined laser beam. The multiplexing method is demonstrated for three laser beams delivering a total laser power of 3 kW. Two concepts for the laser and multiplexer setup are realized. The first aims at an optimized beam quality whereas the second takes the demands of a flexible work tool into account. Both systems are using optical fibers for the beam delivery to the workstation. The requirements for delivering high power laser beams by optical fibers are discussed. Applications in laser beam welding of aluminum and stainless steel are shown.

An Nd:YAG laser with 1 kW average power, 180 J pulse energy, 60 kW pulse power and with 600 micrometers diameter fiber optic beam delivery has been developed. Applications include 4.8 mm deep seam welding at 50 mm/min and 5 mm thick metal cutting at 400 mm/min. Using pulse superposition of unequal and or delayed pulses provides a simple and effective way of shaping the time profile of the pulse, which can be of advantage for special welding applications. Energy is measured on line by means of a wedged beam sampler, an integrating sphere, an optical fiber and a photodiode. Regarding the beam delivery optics, special care must be taken to minimize reflection losses. Anti-reflection coating of fiber end faces was investigated. Though the peak power density 30 MW/cm² is lower than what has been reported as a routinely achievable damage threshold, the tremendous energy density 90 kJ/cm² poses problems. In view of the relatively small area of the fiber, end face cleaning and surface adhesion are critical. Two high power processing head objectives were developed to image the fiber end face onto the work piece.

Efficient laser emission of flashlamp pumped Nd:YAG and Nd:YAP rods at a wavelength of 1.444 micrometers (1.434 micrometers ) is reported. This wavelength is of particular interest for medical applications due to the high water absorption coefficient of 26 cm^-1. A maximum average output power of 100 W at pulse energies of 5.5 J and overall efficiencies of 1.3% was achieved. The 1.444 micrometers performance as well as the output characteristics at 1.064 micrometers and 1.32 micrometers of Nd:YAG were investigated for different pump cavity reflectance materials and spectral filters as a function of doping concentration and rod diameter. The physical properties of the 1.444 micrometers emission line are discussed.

In this paper, the parameters which influence the output power and beam quality of high power solid state laser are analyzed. The optimized model for multi-rod high power solid state laser is built up. Experiments agree to the optimum resonator. From a two-rod laser system, we get a 400 W laser beam with a 5.6 mrad divergence angle. From a three-rod laser system, we get 860 W output power.

The transmission properties of different types of all-silica fibers are investigated, using a multimode high-power cw Nd:YAG rod laser with 2000 W output power. The dependence of the output upon the input beam parameters, waist diameter and divergence, and the resulting power transmission are given. The upper limits for the maximum beam parameters and maximum laser powers, which can be coupled without loss into fibers with certain numerical apertures, as well as the dependence of the output beam profiles upon the intensity distribution at the fiber input are briefly discussed. An experimental set-up is presented, whereby the beam parameters are chosen and the measuring procedures are performed as suggested by the ISO. The waist diameter at the fiber end face, dependent on the laser power, is observed, so controlling the influence of the spherical aberrations of the fiber coupling lens systems. The end faces of polished and cleaved fibers are compared.

A pulsed single rod Nd:YALO-double-pass-amplifier with phase conjugating SBS-mirror delivered 125 watts with a beam quality near the diffraction limit. The thermal lens of the rod with focal lengths of less than 15 cm was dynamically compensated.

Different unstable resonator schemes are described, taking into account that the laser rod acts like a varying thermal lens. The single rod resonators can be extended to contain two or three rods. With 150 mm X 10 mm Nd:YAG rods, the presented resonator designs were investigated experimentally. Output power and beam parameter products as well as the influence of the thermal lens on the focusability were measured. The sensitivity of output power and beam steering to mirror tilt is presented and the design of the variable reflectivity mirrors is described.

The propagation characteristics of several beam radius definitions have been investigated analytically, numerically, and experimentally with regards to their applicability for high power solid state lasers with stable and unstable resonators and to the measurement with CCD cameras. Only for the second-moment radius a propagation law can be derived, which is valid for arbitrary partially coherent, paraxial beams. The same propagation law can be applied to the more useful power-content radius definition solely in the case of beams with non-varying profile such as produced by stable multi-mode resonators. For beams with varying profiles (such as produced by lasers with unstable resonators) a method is presented that allows the estimation of power-content radii behind cylindrical ABCD systems.

We have generated approximately 100 watts of frequency doubled light from the output of an electro-optically Q-switched, diode-pumped Nd:YAG slab laser oscillator operating at an average power of 200 watts (2.5 kHz repetition rate, 80 mJ/pulse, 25 ns pulsewidth). The Q- switch was a compensated z-axis propagation LiNbO₃ electro-optic modulator, and the frequency conversion crystal was a thin slab of KTP. In addition, Q-switched operation at an average power of approximately 250 watts with 26 ns pulsewidths has been demonstrated.

In this paper we discuss progress toward the development of kilowatt-class diode-pumped lasers with beam quality approaching the diffraction limit. The development of high- efficiency, high-brightness lasers will open new applications for precision laser machining. The design and performance of diode-pumped Nd:YAG lasers with average powers in the kilowatt range are addressed. Fibertek, Inc. is presently developing laser systems at this power level for industrial applications such as drilling, cutting, and welding. This work has a goal of producing 0.5 to 2.5 kW average power with less than four times diffraction-limited beam quality (2.6 mm - mr, D(Theta) /4). Both rod and slab architectures are under development. This talk covers initial results with diode-pumped rod lasers operating at up to 500 W average power.

A diode-pumped Nd:YAG laser for use as a driver for a soft x-ray projection lithography system is described. The laser will output 0.5 to 1 J per pulse with about 5 ns pulse width at up to 1.5 kHz repetition frequency. The design employs microchannel-cooled diode laser arrays for optical pumping, zigzag slab energy storage, and a single frequency oscillator injected regenerative amplifier cavity using phase conjugator beam correction for near diffraction limited beam quality. The design and initial results of this laser's activation experiments are presented.

High average power continuously pumped Nd:YAG Q-switch lasers in rod geometry were investigated. A polarization coupled resonator, intended for use in combination with polarizing switches, offers about 80% of the output power available from the equivalent resonator without a polarizer. Mechanical Q-switching by means of rotating wave plates was realized. Stable acousto-optic Q-switching of unpolarized resonators comprising one, two, or six rods was obtained within a wide range of parameters. The pulse duration varied from 150 to 1500 ns, the maximum average output power was 1.7 kW. The experimental results were well in agreement with theoretical estimations. Laser beam delivery through 600 micrometers fibers for laser materials processing was realized.

Currently flashlamp-pumped Nd:YAG lasers operate at a pulse repetition rate of 10...50 Hz. However, some applications call for increasing pulse repetition rate up to 300...500 Hz. Lasers with high repetition rates may be of practical interest to use in hydrography, lidars, locators, and bathimetric systems. We present the design and the performance of a compact high repetition-rate Nd:YAG oscillator pumped by single flashlamp in electro-optical Q- switched operation with second harmonic generation (SHG).

The spectroscopic properties of F³⁺ ions in tetrahedral sites in garnets, together with the good packing of these sites around the dodecahedral position occupied by rare-earth ions, favor a very efficient energy transfer from Fe³⁺ to TM³⁺. Since Fe³⁺ does not introduce additional losses, this ion is a potential sensitizer for Tm³⁺ laser emission.

A study on Nd:YAG media active laser pumped with millisecond variable pulses in free- running generation and passive Q-switched regime is presented. Different resonator configurations were used: stable plane-plane and spherical-plane resonators usually with reflectivity mirrors or with super-Gaussian variable reflectivity mirrors (VRM) as output couplers and super-Gaussian unstable resonators. In Q-switching operation, laser emission consists in trains of 20 - 50 nanosecond pulses with repetition frequency of 20 - 200 KHz. Peak power pulses of 0.5 - 1 MW were obtained and the laser energy contained in a train of pulses varies from 1 to 8 J depending on the length and energy of the pumping pulse. The beam quality of the Q-switched laser was studied comparatively with free-running laser operation.

In this paper, two types of prism resonators, namely, the resonator with a 90 degree(s) prism and a HR/R-coated plane mirror, and the resonator with a 90 degree(s) prism, a triple prism and HR/R mirror, have been studied in detail including: (1) the polarization properties of the prism resonators used for slab lasers were analyzed by means of the Jones matrix calculus and then confirmed experimentally; and (2) numerical calculations of the diffraction integral were performed, using the fast Fourier transform (FFT) method, to illustrate the resonator mode characteristics.

In this paper the design of two different graded reflectivity mirrors is described. Using the thickness variation of the middle layer of a symmetrical (H L)² H stack, a superGaussian reflectance profile was obtained. The dependence of the superGaussian parameters on the deposition geometry was investigated and the results are discussed by comparison with an other graded reflectivity mirror, for which the thickness of the overall high reflecting coating presents a radial variation. The design of a graded reflectivity mirror with a parabolic reflectance profile is also given. The dependence of the parabola parameter on the deposition geometry was calculated for the same deposition conditions.

The investigation of the possibility to influence the output beam parameters of single-mode lasers by methods of intracavity adaptive optics was carried out. Intracavity adaptive mirrors can compensate static and dynamic aberrations of the resonator optical elements. At the same time such mirrors can allow the spatial configuration of cavity to form with the higher filling of laser medium and lower diffraction losses of the fundamental mode.

It is shown that optical phase conjugation with the great reflectivity of the weak signal wave can be obtained without the conjugate reference waves in schemes based on parametric instability of stimulated Brillouin scattering in the system of intersections of power pump wave and weak signal wave. Consideration of schemes with two and more beam intersections is presented. Both cases of intensive and weak waves with equal and different frequencies, and the case when one or both waves are wideband, are investigated. The parametric instability conditions determining parametric generation are obtained. The depletion of the pump wave is taken into consideration. The reflectivities and thresholds of the weak signal wave as a function of the pump wave intensity are determined. It is shown that for equal frequencies of pump and signal waves (omega) _L1 equals (omega) _L2 an increase of the intersecting number N increases the scheme sensitivity and reflectivity. For (omega) _L1 does not equal (omega) _L2 these parameters weakly depend upon N. It's shown that spontaneous emission noise limits the ultimate sensitivity of these schemes at high pump intensities.

A reduction of the divergence of a laser beam by a factor of 2 - 2.5 was achieved in a multimode regime of laser generation using an intracavity controlled mirror. It was shown that various radiation mode structures may be formed at the laser output and in the far-field zone. The correspondence between the shape of deformed flexible mirror and configuration of generated mode has been detected.

A new configuration of laser resonator is proposed. By the intensified radial and azimuthal optical coupling mechanisms involved the optical inhomogeneity caused by the imperfect quality of the laser rod and the thermal induced effect can be made uniform. This may be a new way to improve the beam quality of high power laser.

The paper discusses the factors affecting the pump quantum efficiency for three-micron stationary emission in concentrated Er systems, driven by the up-conversion processes from the terminal laser level. It is shown that in the stationary regime analytical formulae for the quantum efficiency could be obtained as a function of pump conditions and global efficiency of the cross-relaxation processes. These formulae enable a selection of the active medium and pump conditions in order to obtain high pump efficiency.

As a result of growth parameter's optimization high optical quality lithium niobate single crystals with a diameter of 80 - 85 mm and a cylindrical part length of 110 mm were obtained. Investigations of the optical perfection of crystals were carried out by conoscopic method and light spontaneous parametrical scattering method. Lithium niobate single crystals are characterized by satisfactory optical quality for an application in production of optical elements for near infrared spectral region.

A large volume XeCl discharge pumped laser is studied by using several self-consistent models differing for assumptions regarding vibrational kinetics of HCl in the discharge mixture, volume stability, and microarc formation. Volume stability is studied by modeling the discharge plasma as a parallel resistor network, while a single microarc is introduced as a further network element with zero surface. It is stated that only models including microinstabilities as well as an accurate description of HCl vibrational kinetics could be used for large volume XeCl laser devices.

This paper describes the design, development, and construction of an automated control system for high average power excimer lasers working in an industrial environment. The control system is based on a distributed network of transputers, each dealing with its own area of responsibility. This modular approach was chosen to provide maximum flexibility, allowing the control system to be optimized for particular lasers or special requirements. The development of monitoring and actuating equipment suitable for the unusual demands of an excimer laser is also an essential part of the overall project. Some of the monitoring equipment used is standard, while some has been designed and built at Salford. In particular, a 100 MHz bandwidth optical fiber current sensor has been developed to measure the discharge current. Communications between the sensors and the transputer network are almost entirely optical, with special circuits designed at Salford to convert standard sensor outputs into optical signals. Several different systems are used, according to the response time required.

The paper is dedicated to a supersonic e-beam sustained cw CO laser. An analytical model of such a laser is presented. A comparison of the model with results of experimental testing of a full-scale mock-up of the laser is given. In experiments radiation power of 140 - 200 kW with an electro-optical efficiency of 44 - 49% have been obtained with duration of cw operation up to 1 sec.

NovaTube^TM is the result of many years of extensive material research at Lambda Physik to develop a laser cavity of quasi sealed-off laser performance. As test data demonstrate the operating costs can be cut 10 times using the new tube. Test runs in the laboratory have culminated in 10⁹ shots operation on a single gas fill achieved with a 50 W KrF laser.

This paper reports a systematic evaluation of the effects of a wide range of gaseous contaminants introduced in the lasing gas on initial laser power and on gas fill lifetimes. The impurities studied and their relative concentrations were chosen on the basis of the probability of their occurrence in the lasing gases. These were assessed individually and also in common combinations, such as N₂/O₂ simulating an atmospheric leak. Investigations into using novel buffer gas mixtures have shown that increases in operating efficiencies can be achieved. This has been correlated with lasing gas analysis, which has revealed that the rate of internal impurity generation is dependent on the buffer gas composition.

We report here what is to our knowledge the first demonstration of multikilohertz SBS phase conjugation of copper vapor lasers. SBS reflectivities of 90% have been achieved, discounting the energy lost due to the process transient threshold, and phase conjugation performance has been maintained at 6.5 kHz for several hours. The dependence of the SBS performance on CVL beam quality has been investigated and a significant improvement with improved beam quality is obtained. The ability of the SBS reflection to compensate for CVL aberrations has been demonstrated with a phase conjugate fidelity of 0.97. Results of an investigation into the effects of absorption in the SBS medium have shown that an absorption of approximately 10^-3%cm^-1 is sufficient to degrade the SBS performance. Medium agitation techniques have been used to partially overcome the effects of absorption, and techniques for further improvement are discussed. Methods of improving the efficiency of the SBS process, including the use of multiple cells to reduce the transient threshold and operation with higher pulse energies are discussed.

The performance of a high power gas dynamic laser facility for application in technology in branches of heavy industry using high energy consumption and large scale equipment is described. The design of a supersonic diffuser which allowed us to obtain high pressure recovery is presented. Preliminary results of gas dynamic laser test runs are provided.

The results of investigation of UV ((lambda) equals 271 nm) Cu vapor laser sum frequency ((lambda) 1 equals 510 nm, (lambda) 2 equals 578 nm) generation in crystal DKDP are presented. For interaction type ooe the mean UV power about 0.2 W and conversion efficiency (eta) is congruent to 2.5 divided by 3% are obtained for laser mean power about 7 W. Beam divergence, yellow and green line pulse amplitudes, and relative delay are of key importance for sum frequency generation. Optimization of standard 20 W mean power Cu vapor laser was necessary for efficient frequency conversion. The possibility of creating 5 divided by 10 W source of UV radiation is shown, using Cu vapor laser sum frequency generation in DKDP.