8th Intl Symp on Gas Flow and Chemical Lasers

Characteristics of amplification of ultrashort laser pulses in excimer media

Fumihiko Kannari, Minoru Obara

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Energy extraction in XeCl amplifier is theoretically studied for 0.16- and 3-ps initial laser pulse durations. Since an amplification gain is defined by the degree of matching between a gain spectrum and a propagating laser pulse spectrum, when a laser pulse is amplified by a gain medium with a multilined and inhomogeneously broadened spectrum, the saturation behavior of the amplified energy depends on characteristics of change in the laser spectrum during the amplification. Therefore, a saturation energy cannot be simply defined as a unique value for certain initial laser pulsewidth, and depends on amplification history of the pulse, amplified laser energy level, and initial carrier freqency. When a laser pulse is amplified to extremely high energy level ( > 5 mJ/cm2 ), the laser pulse spectrum, which is filtered by the gain spectrum in small-signal amplification regime, is nonlinearly distorted and tends to shift its peak to the red spectrum side.

Study of the interaction of a high-power laser radiation and a transparent liquid

Anne-Patricia B. Alloncle, Jacques Viernes, Daniel Dufresne, et al.

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This paper is concerned with a basic study of vapor bubbles induced by a high power laser beam. It described preliminary studies which should lead to the validation of a laser/ matter interaction code and an hydrodynamic code by optical cavitation experiments. In a first time the experimental arrangements for the generation of a centimeter bubble and for the diagnosis are presented. Visualisations of shock waves and bubbles, pressure and energy mesurements leading to determine a distribution of energy are shown. Then a moderation of the energy depositing and its insertion in a laser/ matter interaction calculation code is presented. A version of the hydrodynamic calculation code PISCES adapted to the study of vapor bubble dynamic and propagation of pressure waves generated during the breakdown and during the collapses is then described (utilization of a multiphase equation of state adapted to the problem).

Measurements of atmospheric transmittance of CO2 laser radiation

Vladimir N. Aref'ev

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The field measurement of transmission of 12C16O2 , 12C18O2 and 13C16O2 laser at 62 wavelenghts in the 9.2-11.2 ?m spectral range are presented. The measurements were made on a 0.2-2.0 km horizontal path using a tunable CO2 laser. The results were compared with the computed molecular absorptions. Rather a good agreement has been found. Under sufficient visibility (disregarding aerosol attenuation) atmospheric water vapour is the main extinction component within 10-13 ?m and in the range of 8-10 ?m other small constituents are importent.

Theoretical study of the high-power pulsed vibrational overtone HF chemical laser

Shu-ichi Ashidate, Toshiaki Takashima, Fumihiko Kannari, et al.

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We have theoretically investigated the output performance of the pulsed discharge initiated H2/SF2 nonchain and H2/F2 chain first vibrational overtone HF chemical lasers.

Spectroscopic measurements of plasmas temperature and density during high-energy pulsed laser-materials interaction processes

Dominique Astic, Patrick Vigliano, Michel L. Autric, et al.

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This paper concerns the characterization of a plasma by spectroscopic method. The study uses a spectrograph coupled to a gated optical multichannel analyzer (O.M.A) in order to obtain temporally and spatially resolved optical emission spectra of laser-induced aluminum and carbon plasmas. Laser-produced plasmas are described with Local Thermodynamic Equilibrium (L.T.E) assumption. Electron temperature and density informations are evaluated from spectroscopic records. Absorption coefficients have been estimated for CO2 and visible radiations

Boiling process in PMMA irradiated by CO2, DF and HF laser radiations

Rene C. Joeckle, Gerard Rapp, Andre Sontag

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When irradiated by a low fluence IR laser radiation, a PMMA plate becomes mat. The damage results from the in-depth absorption of the laser light, which yields a microscopic boiling process. The aspect of the trapped bubbles shows the importance of the absorption depth, which varies with the lasers taken into account (CO2, DF and HF). The threshold of this boiling process has been measured as a function of the incident power density for the three lasers considered. The behaviour is conduction-dominated in the case of the C02 laser radiation and absorption-dominated in the case of the DF and HF laser radiations.

Comparison of high-current discharges with axial and transverse gas flow for UV ion lasers

Sergey V. Babin, Andrey E. Kuklin

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To improve output characteristics of CW ion lasers a transverse flow (TF) and an axial flow (AF) of atoms are applied. Both discharges have improved lasing characteristics in regard to conventional one. The effects of flow are discussed.

Influence of gas composition and pressure on the pulse duration of electron beam controlled discharge XeCl laser

Jan Badziak, Wieslaw Drazek, Adam Dubicki, et al.

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The influence of pressure and composition of Ar+Xe+HCl mixture on the pulse duration of electron-beam-controlled discharge XeCl laser was experimentally investigated. It was found, that the variation of total pressure of the mixture of fixed composition can be the effective and simple way of controlling the pulse duration in the range of one order of magnitude without significant changes of the pulse power

Spatial and electrical characteristics of capacitively ballasted rf laser discharges

Howard J. Baker, Ian Laidler

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A discharge cell has been used to simulate conditions in fast flow, radio-frequency excited CO2 lasers using dielectric electrodes. The frequency dependence of the discharge structure and the Alpha to Gamma transition has been observed in the range 13 - 40MHz. The radio frequency, the thickness of the dielectric layer, and the parallel capacitance of the matching circuit are all shown to control the discharge uniformity and excitation conditions at the centre of the discharge.

Possibility of long population inversion in active media for IR chemical lasers

Boris D. Barmashenko, Viatcheslav A. Kochelap

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Theoretical investigation shows that during the chemical pumping of high vibrational levels of diatomic molecules partial population inversion between these levels can exist much longer than that for vibrational transition 1?0. In case of fast VV-exchange the ”long" inversion appears long after finishing of the inversion for the transition I?0. It lasts up to the completion of chemical pumping reaction. The calculations are made for H2-F2-He mixture.

New emission spectra from chemically excited oxygen and potentiality as a visible chemical laser

Roger Bacis, Jean C. Bonnet, Annie J. Bouvier, et al.

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The interaction of chemically generated metastable oxygen on various metals is examined. Spectra in the visible and the infrared are presented. A blue luminescence is seen for the first time. Small polyatomic molecules are probably responsible. An unsuccessful search for a laser effect has been made on a high power O2(1?g) generator.

Quantitative analysis of a CO2 laser beam by PMMA burn patterns

Rene C. Joeckle, Axel Koeneke, Andre Sontag

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A quantitative knowledge of the threshold fluence of surface damage produced by the CO2 laser irradiation of a PMMA plate enables us to design a simple method of measuring the power density distribution in a CO2 laser beam. By varying the irradiation times, one obtains several burn patterns, each of them characteristic of a well-defined power density. The power density distribution can then be drawn. This method has been used for studying the power density distribution in several high-power laser beams. Although it is non-instantaneous, this simple and cheap method offers a large spatial resolution and gives interesting results when compared to sophisticated CO2 beam analysers.

Very high reflective all-dielectric coatings for high-power CO2 lasers

R. M. Berger, Martina Chmelir, Herman E. Reedy, et al.

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With the output power of CO2-Lasers still increasing, the optimization of optical components becomes even more important. In todays high power lasersystems the optics have to withstand power densities of typically 1 kW/cm2 and more, thus absorption has to be kept at a minimum. If not, problems such as distortion of the optical surface, loss of mode control, loss of output power, thermal focusing in the output beam or even damage to the whole system might occur.

Aspects of keyhole/melt interaction in high-speed laser welding

M. Beck, Peter Berger, Friedrich Dausinger, et al.

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The increasing availability of highest power lasers broadens the economic use of deep penetration laser welding by increasing maximum welding depth and by increasing welding speed. The problems encountered in those two areas of interest differ significantly. Whereas the maximum welding depth is strongly affected by the absorption mechanism1,2, the maximum welding speed is limited by fluid dynamic phenomena . Theoretical modelling allows to seperately investigate the different processes.

Photoinitiation of chemical lasers using radiation from a cylindrical surface discharge

R. E. Beverly III

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A cylindrical surface-discharge device has been developed to produce intense UV/VUV pump radiation for studying photoinitiated and photolytically pumped gas laser schemes. A homogeneous, high-temperature (T ~ 20-30 kK) plasma is formed adjacent to the interior surface of a dielectric cylinder by an electric discharge. Initial experiments have emphasized electrical, gasdynamic, and spectral characterization

Recent advances in excimer laser technology at Los Alamos

Irving J. Bigio, Stephen J. Czuchlewski, Andrew W. McCown, et al.

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Current research in excimer laser technology at Los Alamos progresses in two major areas: 1) In the Bright Source program, the development of ultra-high brightness (sub-picosecond) laser systems, based on discharge-pumped excimer laser amplifiers, continues. Recently we have completed rigorous measurements of the saturation parameter for ultra-short pulses. 2) In the laser fusion program, implementation of the large KrF laser fusion amplifiers have been accompanied by numerous studies of the laser physics and kinetics of large e-beam pumped devices.

Small-signal gain in the oxygen-iodine laser

Willy L. Bohn, Keith A. Truesdell, W. Pete Latham, et al.

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A simple model for predicting the small signal gain as a function of flow direction is presented. It basically couples simplified kinetics and fundamental gas dynamics and allows for the heat release produced by the water deactivation of excited oxygen and iodine. The numeric results lead to a temperature rise in the gas, which causes a substantial decay of the small signal gain in flow direction. An analytic solution is also derived and results of both approaches compare favourably with experimental data.

Thermal lensing effect in fast-axial flow CO2 lasers

M. Moissl, R. Paul, K. Breining, et al.

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Numerous industrial applications require high power lasers with at the same time high beam quality. Therefore, among other requirements of the laser design and operation particular attention has to be paid on the optical properties of the laser-active medium.

Efficient e-beam sustained Ar:Xe laser

Hako Botma, Peter J. M. Peters, Wilhelmus J. Witteman

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An efficient atomic Xe laser pumped by a combination of an e-beam and an electric discharge has been made. In the present study we investigated the laser operation as a function of gas pressure. The best results were obtained at a pressure of 7-8 bar under optimized excitation conditions. The specific output energy reached 10 J/l and the specific laser power 12 MW/1. The efficiency is about 2%. When both e-beam and sustainer current are present simultaneously the efficiency can rise to 7-9% in a 0.25 |?s interval.

Pulsed HF chemical laser using a VUV phototriggered discharge

Henri Brunet, Michel Mabru, J. Rocca Serra, et al.

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A simple corona phototriggered discharge has been operated in SF6/C2H6/Ne mixture at typical pressures 90-110 Torr, deposited energies up to 180 J/l and has resulted in the production of high energy HF laser pulse aroung 2.8 ?m. The maximum laser energy was 3.8 J per pulse which corresponds to a specific energy of 7 J/liter and to an efficiency of 4 % based upon the energy stored on the sustaining capacitor. Results of discharge modeling have shown that F atoms were mainly produced by electron excitation of SF6 dissociative electronic states.

Influence of mixing on the characteristics of the oxygen-iodine laser

A. N. Dvoryankin, Yuri A. Kulagin, N. Yu. Kudryavtcev

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Two-dimensional numerical modeling of the influence of mixing on the characteristics of the oxygen-iodine active medium is done. Gain coefficient distribution is obtained for the side-wall slit and parallel schemes of the iodine injection into the planar flow of singlet oxygen.

Test of Geltman theory of multiple ionization of xenon by intense laser pulses

Riccardo Bruzzese, V. Berardi, C. de Lisio, et al.

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The intensity dependence of the multiphoton ionization spectra of Xenon atoms has been investigated with an improved accuracy and well controlled laser parameters. In particular, we have examined the ionization rates for Xe3+, Xe2+, X+ as functions of the laser intensity and gas pressure in the target chamber. The apparatus used for these measurements is characterized by a high energy resolution and a completely digital acquisition system. The ionization rates of the different ions have been used for testing the basic assumptions of the Geltman theory of multiple ionization based on the single electron ionization model.

Chemical generation of electronically excited nitrogen N2(A3 sigma +u) and lasers on electronic transitions

A. N. Dvoryankin, V. N. Makarov

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Recent advances in the development of electronic energy transfer (EET) oxygen-iodine lasers led to attempts to discover new donor-acceptor pairs in order to create chemical EET laser of the visible band. From this point of view H2-F-HN3 and H2-F-NF2 flames attract much attention.

Gas-dynamically cooled CO laser with rf-excitation: design and performance

Hartwig von Buelow, Eberhard Zeyfang

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A gasdynamically cooled CO - laser with a dielectrically stabilized RF -discharge in the subsonic region is described and experimental results are presented. The gas is excited at pressures of about 500 mbar in a discharge tube with a rectangular cross - section. Then, the laser gas is cooled to a temperature of approximately 90 K by an adiabatic expansion in a two - dimensional supersonic nozzle. After extraction of laser energy in a triple pass resonator the gas is recompressed in a supersonic diffuser and by a Roots pump system. The dependance of laser power on discharge pressure and resonator design is presented. Experimental results of the diffuser performance are also discussed.

Power gain characteristics of discharge-excited KrF laser amplifier system

Choo Hie Lee, Boo-Yeon Choi

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Amplification chracteristics of a discharge excited KrF laser with UV-preionized were investigated. The power gain(Iout/Iin) of a single-pass amplifier system were 20, 7 for input intensity of 50 kW, 0.5 MW, respectively. The small signal gain, absorption coefficient, and saturation intensity were calculated by one-dimensional propagation amplifier model. The KrF* formation efficiency, the extraction efficiency, and the power efficiency were also obtained with this numerical model.

Solar-powered blackbody-pumped lasers

Walter H. Christiansen, J. Marcos Sirota

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A concept for a solar-powered laser is presented which utilizes an intermediate blackbody cavity to provide a uniform optical pumping environment for the lasant, typically CO or C02 or possibly a solid state laser medium. High power cw blackbody- pumped lasers with efficiencies on the order of 20% or more are feasible. The physical basis of this idea is reviewed. Small scale experiments using a high temperature oven as the optical pump have been carried out with gas laser mixtures. Detailed calculations showing a potential efficiency of 35% for blackbody pumped Nd:YAG system are discussed.

Quartz gauge and ballistic pendulum measurements of the mechanical impulse imparted to a target by a laser pulse

Jean-Yves David, J. C. Wettling, Patrick Combis, et al.

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A laser impact striking a target with a sufficient irradiance generateg a thermo-shock. It is possible to measure the amplitude of this shock as a function of time with a quartz gauge . The integration of this pressure signal gives a first estimate of the mechanical impulse imparted to the target. It is also possible to achieve this by measuring the speed of the gravity centre of a ballistic pendulum. The momentum amount of the mobile set m?v? is a first approximation of the mechanical impulse. However,for more accurate measurement it is necessary to take into account the moment of inertia and the position of the gravity centre with respect to the rotation axis.

Continuous chemical lasers of visible region

A. N. Dvoryankin

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Now powerful lasers of UV region on electronic transitions of excimer molecules1 RX*,RR* where R is rare-gas atom and X - halogen, are created. Emitting molecules are produced during chemical reactions between electronically excited (EE) atoms R* and halogen-containing molecules.

Laser welding of INCONEL 600

Giuseppe Daurelio, G. Dionoro, F. Memola Capece Minutolo

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Laser beam welding exhibits features typical of autogenous welding by fusion with very concentrated heat sources: narrow deep weld, restrict heat affected zone (HAZ), negligible residual.stresses etc. All these aspects are of great importance in welding special purpose alloys such as corrosion resistant nickel base alloys. In this work, a nickel base alloy INCONEL 600 has been welded by means of a 2 kW CO2 cw laser. In order to evaluate the influence of the basic welding parameters on heat affected zone, weld structure and weld geometry, an accurate analysis has been carried out. The experimental results show a strict correlation between the power beam and the welding speed vs. the weld bead geometry. As the speed increases, so penetration decays. Microhardness tests, micro and macrograph examinations did not reveal, in the range of experimental parameters, any significant alteration in weld bead structure nor the presence of a HAZ. In order to assess process efficiency, the experimental data were processed using the Line Source Model (LSM) which permits to calculate the Melting Ratio (MR) and Energy Transfer Efficiency (ETE).

New photovoltaic effect in semiconductor junctions n+/p

E. Dominguez Ferrari, F. Encinas Sanz, Jose M. Guerra Perez

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The application of multiphotonic multistep absorption model to the 10,6 ?m wave lenght laser induced photovoltaic potentials in silicon junctions is discussed. First observations in Germanium junctions are reported.

Surface quenching of singlet delta oxygen

R. P. Crannage, Daniel E. Johnson, Ernest A. Dorko

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Singlet delta oxygen has been generated in a microwave discharge and passed into a cylindrical Pyrex flow tube. Detection of emission from the gas stream at 1.268m was accomplished before and after flow through the tube. The quenching coefficient for a Pyrex surface and the gas phase quenching rate constant for ground state oxygen were determined by this procedure.

Thyristor driven pulser for multikilowatt lasers

Pieter L. Swart, Hubertus M. von Bergmann

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Excimer- and CO2 TEA pulse lasers require excitation pulses with voltage rise times of 100 ns and peak voltage levels of more than 40 kV for efficient excitation. The corresponding electrical inputs extend to multikilowatt levels of average powers. To achieve these levels, primary switching must be carried out at tens of kA and multiple kV levels and at repetition rates of several kHz. These requirements place extreme demands on the active switching elements employed in the pulser for primary pulse conversion. Under these conditions, thyratron lifetimes are drastically limited and endeavours to overcome these limitations have led to the development of an all solid state driven pulser. The solid state driven pulser employs a modular, thyristor switched, pulse power supply unit for primary pulse conversion and a four stage series magnetic pulse compressor to transform the pulses into a domain compatible with excimer laser excitation.

Magnetic pulse compression in the prepulse circuit for a 1 kW, 1kHz XeCl excimer laser

G. B. Ekelmans, Frederik A. van Goor, M. Trentelman, et al.

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Using high quality low loss ferrite, a single stage magnetic pulse compression network has been demonstrated working at 1 kHz PRF. A pulse compression factor of 4 has been achieved, delivering a 50 ns pulse as prepulse in the excitation circuit for a high power XeCl-excimer laser

Industrial excimer and CO2 TEA lasers with kilowatt average output power

Hubertus M. von Bergmann, Pieter L. Swart

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We have developed a high repetition rate high average power pulsed laser system intended for industrial applications. The system has been designed for operation as an excimer and CO2 TEA laser and is capable of continuous operation at repetition rates of up to 2 kHz. A closed loop gas recirculation system, driven by a large diameter, magnetically coupled, axial fan is employed, providing gas flow velocities of up to 90 m/s. The laser delivers maximum average output powers of more than 500 W as KrF excimer and 2.5 kW as C02 TEA laser.

Experiment and modeling of O2(1 delta) generation in a bubble-column-type reactor for chemically pumped iodine lasers

Oren Aharon, A. Elior, M. Herskowitz, et al.

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Experiments in a bubble column type reactor in a chemical oxygen-iodine laser system applying high flow rates of chlorine mixed with buffer gas have been carried out. A model which accounts for the physical processes in this system is presented. It is shown that the model can describe our system as well as other systems where buffer gas was not used.

Laser interaction with solids

David C. Emmony, Stuart E. Clark, Noel C. Kerr, et al.

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Techniques for measuring the laser induced damage threshold are discussed with particular reference to laser beam profiling and the objective detection of damage. Diagnostic measurements of the damage process as well as the topographical features of the damage site are discussed. Surface modification and laser preconditioning are considered.

30-Torr pulsed singlet oxygen generator

Masamori Endo, S. Arai, T. Yamashita, et al.

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A high-pressure pulsed chemical oxygen generator which yields higher than 30Torr of 02(a1?g) is developed. On typical operational conditions, O2(a1?g) pressure rises up to 34Torr in the first 20ms, followed by the slower decay. A simple model calculation showed good agreement with experimental results. The feasibility of the lasing action between O2(a1?g) and O2(X3?g-) was discussed based on this model calculation.

Large volume XeCl laser with longitudinal gas flow: experimental results and theoretical analysis

Sarah Bollanti, Paolo Di Lazzaro, Francesco Flora, et al.

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In a large volume XeCl laser with longitudinal gas recirculation system, the tecnique of discharge photo-triggering has been successfully applied. Flow characteristics and laser performances, included gain profiles spatially and temporally resolved, are here described. Moreover, the results of a simplified simulation code are compared with the experimental ones.

Fast-flow gas-dynamic effects in high-pulse repetition-rate excimer lasers

Philippe Ch. Delaporte, Bernard L. Fontaine, Bernard M. Forestier, et al.

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Acoustic and aerodynamic phenomena may play a leading role in high average power excimer laser as soon as a high pulse repetition rate is envisioned. This general lecture summarizes the studies achieved at IMFM on this topic.

Excimer laser ceramic and metal surface alloying applications

Elias I. Hontzopoulos, A. Zervaki, G. Zergioti, et al.

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Recent excimer laser based deposition and surface modification techniques for ceramic and metallurgical engineering applications are reported. These include the improvement of the anti-corrosion and erosion properties and wear resistance of metal alloys and the formation of surface conducting patterns on ceramic materials. Excimer laser chemical vapour deposition (LCVD) applications B, Al and Hf or multielement combinations are discussed together with studies which aim at a better understanding of the fundamental processes governing the deposition process

Development of chemical oxygen-iodine laser for industrial application

Hiroo Fujii, Masahiro Iizuka, Mikio Muro, et al.

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Since the first oscillation of a ruby laser obtained in 1960, an enormus amount of efforts have been concentrated on laser researches. Fundametal researches were almost finished in 1960's, then aims of investigations were turned to find out new applications.

Laser-induced medium perturbation in pulsed CO2 lasers

Gregory C. Dente, Robert F. Walter, Daniel Gardner

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The phenomenon known as laser induced medium perturbation (LIMP) or mode-medium interaction (MMI) is responsible for a loss of nearly 50% of the output energy from a focussed far-field spot in some pulsed CO2 lasers. A simple theory was previously developed to explain this result in terms of the formation of a phase grating in the gain medium due to enhanced vibrational-translational (VT) relaxation heating in regions where the intracavity flux is high. Attempts to employ this simple theory to model recent experimental results and predict and avoid the onset of this loss mechanism in the design of long pulse CO2 lasers demonstrated that it was inadequate for several reasons. In the present work, these shortcomings are examined and a new model is presented which incorporates wave optics and hydrodynamic relaxation effects. The results of calculations with this new model (time dependent Strehl ratio and pressure dependence) are in good agreement with experimental data for both electron-beam sustained and UV-preionized CO2 discharge lasers. This model is capable of determining laser design points which essentially eliminate the far-field energy loss.

Output characteristics of a multikilowatt repetitively pulsed XeF laser

Robert F. Walter, Louis J. Palumbo, Steven W. Townsend, et al.

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Abstract not available.

Chemical oxygen-iodine laser: flow diagnostics and overall qualification

Eric Georges, Roger Barraud, Alain Mouthon

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Since the first demonstration of a CW oscillation of the chemical oxygen iodine laser ( COIL ) in 1978 reported by McDermott et al. numerous research teams are developing various experimental set-ups and theoretical models. The main goal of these studies is to increase the performances of the laser. To determine the characteristics of each laser component, various accurate and calibrated detectors are used . Concentrations and molar flow rates of all the chemical species are determined experimentally . The measurement systems are presented, especially those applied to the evaluation of the water concentration in the flow : hygroscopic solid hygrometer and laser diode spectroscopy . The experimental data allow an overall qualification of the laser . Furthermore, some of them are used in theoretical models and some others are used to demonstrate the validity of these models. As shown in the data exploitation, a precise value for water content in the flow is essential to compute accurately the cold trap efficiency, the chemical power carried by singlet delta oxygen, and to check the influence of water in the kinetical mechanism. One of the key point to optimise the efficiency of the COIL is to solve the mixing problem of singlet delta oxygen and iodine streams . This can be studied by recording with a video system the visible emission of I2 (B => X) produced during the interaction of O2(1?) and I2, and by processing digitized images .

Study of high-average-power excimer laser with circulation loop

Bruno Godard, Emmanuel Estocq, Marc X. Stehle, et al.

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Preliminary studies of an high average power, high energy per pulse, X-ray preionized XeCl laser are presented. A parametric study is given (efficiency and energy per pulse as a function of pressure, charging voltage, capacitance and X-ray dose). We obtained 4 Joules per pulse and the maximum efficiency is 2.5% with 1.7 J. With a circulation loop, 80 Watts has been reached.

Chemically driven pulsed and continuous visible laser amplifiers and oscillators

James L. Gole, J. R. Woodward, S. H. Cobb, et al.

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Two approaches to visible chemical laser development are outlined. An extremely efficient near resonant intermolecular energy transfer from selectively formed metastable states of SiO and GeO to sodium atoms is used to form a sodium atom laser amplifier representing an extension of the outlined concept producing the first visible (535 nm) chemical laser amplifier and oscillator based on a thallium atom receptor. We outline the thallium laser concept and the development of the sodium based energy transfer system for laser amplification and oscillation in the wavelength ranges ~ 569 and 616 nm. In a second approach, we rely on the high cross section (pumping efficiency) highly selective and exothermic sodium trimer-halogen atom reactions to produce continuous sodium dimer laser amplifiers. Optical gain through simulated emission is demonstrated in regions close to 527 (3.8% for individual rovibronic level (? = 8 x 10-3/cm)), 492, and 460 nm (~ 2.3% for indiv. rovibronic level). Potential extensions to the ultraviolet are noted.

Electron density measurements of laser-induced surface plasma by means of a beam deflection technique

Alexander Michaelis, Juergen Uhlenbusch, Wolfgang Vioel

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A laser-induced surface plasma is generated by a Q-switched CO2 laser oscillator amplifier system. At a pulse repetition rate of 20 kHz, laser pulses at 10.6 ?m with 70 mJ pulse energy, 0.2 ?s half-width, 250 kW peak power, an average power of 1.4 kW and TEM00 beam quality are available. At a higher repetition rate of 100 kHz, the peak power and the pulse energy diminish to 15 kW and 14 mJ respectively, and the half-width is with 0.6 ?s three times larger. The spatial and temporal distribution of the electron density in a laser-induced plasma near an aluminum surface is measured by a beam deflection technique. As a laterally probing beam a cw 4 W CO2 laser tuned at 10.2 ?m wavelength is used, whose beam is focused through a small volume in front of the target surface. The electrons of the laser-induced plasma refract the cw CO2 laser beam, and the resulting beam deflection is determined by means of a partially absorbing CaF2 wedge in connection with a fast infrared detector. Simultaneously the plasma absorption of the probing laser beam is measured. A simultaneous detection of the beam deflection and the actual laser power of the oscillator amplifier system gives the possibility to estimate the velocity of the expanding plasma to 103 m/s. Two different kinds of laser- induced discharges were observed. Depending on the conditions the laser-induced plasma leaves the surface or remains attached. Surface leaving plasmas and plasmas attached to the metal surface may be distinguished by the sign of the deflection angle. The electron density in the laser-induced plasma which is responsible for the energy deposition and therefore for the cutting and welding quality can be influenced by the energy and pulse form of the laser pulses and working gases. The electron density reaches 1.1023 m-3 in case of helium as working gas and the dimensions of the helium plasma are about 1.5 mm using laser pulses at 20 kHz repetition rate. The values of the electron density and the dimensions of the plasma are 3 times higher in case of argon resulting in an beam absorption of 80 % in the plasma compared to about 20 % in case of helium. Using laser pulses at 100 kHz repetition rate the electron density in the plasma is reduced by a factor of two due to the lower peak power of the laser pulses compared with the laser pulses at 20 kHz repetition rate.

Pulse shape effects in a twin cell DF laser

Eric K. Gorton, E. W. Parcell, P. H. Cross

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DF laser output pulse shape effects observed when a pulsed twin cell TE laser structure is operated with variable delay between cells are reported. The pulse shape effects can be understood as a result of the timing of the lasing on differing vibrational bands and also as a result of the creation of ground state DF molecules.

Characteristics of a downstream-mixing CO2 gas-dynamic laser

Takashi Hashimoto, Susumu Nakano, Michio Hachijin, et al.

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The performance of a combustion-driven downstream-mixing C02 gasdynamic laser (GDL) has been developed. A small-signal gain coefficient up to 0.6%cm-1 and a laser output power as high as 11 kW have been measured, on the condition that the total mass flow rate and combustion gas temperature were about 2 kg/s and 1750 K, respectively. To explain the difference between the experimental data and the expected potential, a mixing loss factor was previously introduced. In the present study, further experiments and a numerical analysis are conducted to clarify the phenomena in the laser cavity. Consequently, it is made clear that, under the existent circumstances of supersonic nozzle manufacturing technology, two supersonic flows will not mix well.

High-repetition-rate, multijoule transversely excited atmospheric CO2 laser

Hidekazu Hatanaka, Nobuo Kawahara, Katsumi Midorikawa, et al.

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The high-repetition-rate operation of a transversely excited atmospheric CO2 laser pumped by an all-solid- state exciter consisting of a three-stage magnetic pulse compressor has been tested. At a repetition rate of 140 pps, an average laser power of 1.2 kW was obtained with an overall efficiency of 7.6%. For further increase of the repetition rate, influence of density perturbation on laser performances (discharge stability, laser output energy and beam quality) have also been investigated.

Progress toward the demonstration of a visible (blue) chemical laser

John M. Herbelin

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The nitrogen fluoride/bismuth fluoride reaction system continues to be under intensive investigation as an energy source to power a short wavelength (visible blue) laser. The majority of these efforts have centered upon the development of an extensive kinetic database and the successful scaling of the excited state to the densities required for laser operation. Meanwhile, very little is known about the ground state properties, in particular the distribution of the population in the vibrational levels. This work has been directed toward the characterization of this distribution by analyzing the emission from a high "Q" resonator surrounding a 1.5-m pin discharge facility. The results from this study show that the lower-state vibrational 1evels are not fully relaxed and, if one attempts to approximate it by a Boltzrnann distribution, the resulting temperature, T*vib = 1800 K, is substantially higher than the excited state temperature, T*vib = 950 K. Moreover, the intracavity results show that the system is very close to threshold on the 0—3 transition, and that operation of the reaction system at lower temperature and pressure, such as can be achieved in a supersonic flow medium, may be sufficient to produce lasing.

Propagation invariance of laser beam parameters through optical systems

Rosario Martinez-Herrero, Pedro M. Mejias, Jose Luis Hernandez Neira, et al.

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For general multimode laser beams, a number of parameters is derived which are invariant under propagation through ABCD optical systems. Wigner formalism is used and the bidimensional case is considered, The relationship between these parameters and quasihomogeneous fields is also discussed.

Fluid-dynamic perturbations in gas lasers

T. E. Horton

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The magnitudes of the laser pulse induced perturbations in the cavity gas are quantified as a function of system parameters. The conditions for which linear acoustic theory, non-linear acoustic theory, and shock gasdynamic theory represent accurate descriptions of these thermally driven acoustic phenomena are delineated. For gas flowing through a laser cavity, expressions are presented which relate instantaneous perturbations of local velocity to those of density. These cover both acoustical disturbances and hydrodynamic events such as turbulence. The non-flow limit is also examined.

High-power CO2 laser excited by 2.45 GHz microwave discharges

Bernhard Freisinger, Markus Pauls, Johannes Heinrich Schaefer, et al.

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Excitation of C02 : N2 : He gas mixtures of a ratio 4.5:13.5:82 by means of microwave discharges (2.45 GHz) leads to powerful laser action. Experiments in systems of axial type with superimposed fast axial flow and the electric field perpendicular to flow and laser beam are performed varying the microwave power, gas pressure, geometry of the waveguide and of the discharge. Calculations of the electrical field inside the waveguide filled with plasma and a dielectric tube using the program URMEL-T are compared with results from invasive probe measurements. It is shown, that by proper tayloring of the electric fields very homogeneous discharges are generated. Laser devices with discharge diameter d = 1.6cm, 2.4cm and 5.1cm are studied both theoretically and experimentally. The best result achieved up to now is a 700 W laser output from one module of length L = 0.3m and diameter d = 5.1cm.

Analysis of laser welding process with the mathematical model GMDH

I. de Iorio, Vincenzo Sergi, V. Tagliaferri

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The employment of laser system for very automatized welding processes needs an analysis of physic mechanisms by means of mathematical models that correlate the characteristic quality index of welding to working parameters. In this work we used the Group Method of Data Handling (GMDH) mathematical model in order to correlate, for different kinds of steel, the penetration depth to working parameters, chemical composition and thermal properties of the material. Results showed the very important influence of material composition which, in some cases, can be related to that of the main parameters as beam power and welding speed.

2.5 kHz high-repetition-rate XeCl excimer laser

Ken Ishikawa, S. Takagi, Naomichi Okamoto, et al.

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An XeCl excimer laser was operated at the high repetition rate of 2.5 kHz, which can circulate the laser gas up to 100 m/s uniformly and efficiently. The stable operation at the highest repetition rate, 2.5 kHz, has been attained in Ne buffer at a gas flow rate of 54 m/s with an average laser power of 87 W

Quality control of laser cutting process by surface morphology

Vincenzo Sergi

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Quality control criteria, traditionally adopted for manufactured parts by laser cutting, have related generally to cut characteristics as kerf width, inner side slope of it, heat affected zone extent, dross appearance; all these methodologies require sample examination, appropriately prepared. That can provide useful results on process control only after quite a long time that a possible misworking is happened. This paper propose to adopt the appearance of cutting surface microgeometry as process control method; this morphology has been detected by means of a new rugosimeter which uses a laser beam as stylus, therefore the profile can be measured without contact between stylus and workpiece, while the related measures can be elaborated soon after the carrying out of cut. In this stage of study the methodologies of acquisition and elaboration of experimental roughness profiles, the specification of more significant parameters and the correlation between these last and the main variables of laser cutting process are reported.

Reactive-flow modeling of the H/NF2/BiF reaction system

Robert Acebal, Jeffrey P. Dansereau, Randy C.R. Jones, et al.

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The H/NF2/BiF system is one of the most promising concepts for high-power short wavelength chemical lasers (SWCL). The preferred approach uses the H + NF2 reaction to efficiently generate NF(a) energy-carrier molecules. These latter species interact with Bi compounds to produce excited BiF. The potential lasing transition is BiF(A-X) emitting near 460 nm. We report in this paper one-dimensional (1-D) reactive-flow modeling of the H/NF2/BiF system. This work supports design of an experimental demonstration of continuous-wave lasing in a supersonic-flow, purely chemical system. The model treats the subsonic plenum, transonic throat, and supersonic expansion regions.

Frequency up-conversion of a discharge-pumped molecular fluorine laser by stimulated Raman scattering in H2

Masayuki Kakehata, Etsu Hashimoto, Fumihiko Kannari, et al.

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By exciting 10-atm He/F2 gas mixtures by electric discharge at 66MW/cm3, a specific output energy of 2.9J/1 (83mJ) has been obtained in the F2 laser (157.6nm). To extend an available laser wavelength region with high output laser energies in the vacuum ultraviolet, frequency conversion of the laser radiation by stimulated Raman scattering in H2 has been demonstrated for the first time. The laser energy focused into a Raman cell was about lOmJ (22ns FWHM), which corresponds to the focused intensity of 141MW/cm . At H2 pressure of 5atm, 1st and 2nd Stokes lines (168.6nm, 181.4nm) and 1st anti-Stokes line (147.9nm) were observed. The energy conversion efficiency was ~10% for the 1st Stokes line, ~ 2% for the 2nd Stokes line, and ~ 0.8% for the 1st anti-Stokes line at a l0atm H2.

Design and performance of an atmospheric pressure HF chemical laser

D. Chuchem, Yehoshua Y. Kalisky, M. Amit, et al.

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Performance and design of an atmospheric-pressure, corona-preionized pulsed HF laser is presented. The preionization was achieved by means of a "plasma cathode". Two types of lasers were investigated: A short laser with effective screen area of 50 x 7 mm2, and a long laser with an effective screen area of 100 x 7 mm2. A grounded flat aluminum anode with rounded edges was placed 7 mm from the screen electrode in the short laser and at various gaps (5.8-8.3 mm) in the long laser, thus forming effective discharge volumes of 2.45 cm3 and 3.6 - 5.2 cm3, respectively. The SF6:H2:He gas ratios employed were: 7:2:91 and 5:2:93. Output pulses of up to 40 mJ energy were achieved. Electrical efficiencies up to 2.5% were obtained at about 8 mJ per cm3. The influence of the gas pressure, air contamination, the capacitor ratio and output coupling reflectivity on the laser performance was measured.

Power stabilization of high-power industrial CO laser using gas exchange

Hirotaka Kanazawa, Naohito Yamaguchi, Takuro Nakajima, et al.

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A long time stable operation of a high-power discharge-excited CO laser was attained by controlling a laser gas composition. Firstly, changes of the gas composition during discharge under the sealed-off condition were studied experimentally. On the basis of these results, the conditions of a gas exchange, which lead to the stabilization of the output laser power, were determined. A continuous operation of the CO laser about 1 hour at a power level of 3 kW was achieved with a power instability less than +3 %.

Scaling of self-sustained discharge-excited cw CO laser

Shunichi Sato, Kunimitsu Takahashi, Osama Noda, et al.

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The excitation scheme based on transverse, self-sustained dc discharge has been successfully scaled to obtain a cw CO laser output of more than 5 kW. In this paper reported performance data are reviewed, and output power scaling parameters for the scheme are discussed. Requirements for obtaining an output of 20 kW are given.

Measurements of gas flow and gas constituent in a wind-tunnel-type excimer laser under high-repetition-rate operations

Koichi Kasuya, Kazuhiko Horioka, N. Hikida, et al.

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A low speed wind tunnel type excimer laser apparatus of about 500 liter gas volume was constructed to study the critical issues concerning such kind of high repetition-rate excimer lasers. For the moment, the gas flow speed and the repetition-rate of the KrF laser was up to 50 m/s and 1 kHz, respectively. The gas flow conditions, the gas constituents and the laser output were measured with various methods to clarify the basic processes.

High-power KrF lasers

Michael H. Key, Rene Bailly-Salins, B. Edwards, et al.

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High power krypton fluoride lasers are being developed as an alternative more efficient and more cost effective technology for the production of ultra high power pulses. Novel laser architectures are being evolved for this purpose including the use of angular multiplexing and Raman beam combining. Prototype systems are being developed in several laboratories worldwide and in particular at the Rutherford Appleton Laboratory where the Sprite laser installation has been used to demonstrate operation in an angular multiplexed and Raman beam combined mode for the generation of exceptionally low beam divergence and high power in short pulses. Details are reported of the work with the Sprite system and of design extrapolations which are under consideration as the basis of future larger laser facilities, including the possible European Laser Facility with a performance target in the region of 1 PW peak power and 100 kJ maximum energy.

High-power unstable resonator CO laser

Shunichi Sato, Kunimitsu Takahashi, Ikuzo Tanaka, et al.

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The operating characteristics of a multikilowatt unstable resonator CO laser are described. A positive-branch confocal unstable resonator was applied to a large-volume, transverse, self-sustained dc glow discharge-excited cw CO laser with a closed-cycle, subsonic gas flow. Output power and near-field beam properties were measured for various geometrical output couplings. An output of 5.0 kW has been obtained for a coupling of 0.25 (magnification M=1.16) with an electrical conversion efficiency of 16.9%. It has been revealed that the output from the unstable resonator is comparably high to that from the stable resonator under the same gas and discharge conditions. The output beam patterns and the sensitivity of power to angular misalignment of the mirrors are also reported.

Design, construction, and operation of 65 kilowatt carbon dioxide electric discharge coaxial laser device

James P. Reilly, Michael L. Lander, K. Maxwell, et al.

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The application of laser systems to the investigation of the properties of materials has become an important part of materials research in recent years. The demand for laser systems capable of supplying high-energy, high-quality output beams on a reliable basis has sparked increased activity in the area of research and prototyping of such devices. Accordingly, the design and construction methods used to produce a 65 kdowatt Carton Dioxide Electric Discharge Coaxial Laser (EDCL) device are discussed. Specific design criteria are identified in accordance to the critical performance requirements for the laser device. Furthermore, the unique construction methods and support system requirements essential to EDCL technology are described along with test results. The 65 kilowatt C02 EDCL laser was constructed for the Laser Hardened Materials Evaluation Laboratory of the Air Force Materials Laboratory located at Wright-Patterson Air Force Base, Ohio under contract F33615-84-C-5086.

Study of characteristics of a multikilowatt CO2 laser operating in flow-closed cycle: a semiempirical model

Janusz Konefal

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Basing upon a semiempirical model of the closed-cycle flow-laser the overall analysis of the multikilowatt transverse-flow C02 laser was carried out. Ihe analysis concerns the thermodynamic and gasdynamic characteristics of the gas-flow, quality of the closed flow-channel, efficiency of the compressor operation efficiency, the output laser power level and the possibility of the laser-beam frequency tuning.

Debris plume phenomenology for laser-material interaction in high-speed flowfields

James P. Reilly

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This paper deals with the analytical and experimental determination of the morphology of debris plumes in hypersonic low pressure aerodynamic flowfields. These debris plumes are composed of both gas and solid particulate matter ablated from composite materials by repetitive pulse high energy laser beams. The repetition rate of these individual clouds is determined by that of the incident laser beam. Repetition rates covered in the study range from 10 Hz to 100,000 Hz, and are compared to the steady vapor plume from a CW laser/material interaction situation. Extensive modeling of the coupled gasfrarticulate plume and its expansion into the hypersonic flowfield has been accomplished, and compared to pertinent experiments. These experiments were performed in a large scale hypersonic test facility using high stagnation temperature and stagnation pressure flowfields to produce test conditions with static temperatures in the range 200-300 Kelvin, static pressures in the range 10-4 to 10-1 atmospheres, and freestream test section Mach numbers in the range of two to five. Data will be presented on the behavior of vapor only, particulate only, and combined vapor/particulate plumes injected into such flowfields.

Probe measurements in a CO2 laser plasma

Christophe Leys, P. Sona, Peter F. Muys

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Efficient design procedures for high power C02-laser modules rely on a thorough understanding of the gas discharge as laser source. In this, numerical simulations of the laser plasma can be of substantial help but leave out key features like discharge geometry and gas flow effects. Therefore, efforts should also be put into the measurement of the plasma parameters for a given module. Since Langmuir probes can provide both spatially and time-resolved information on the plasma, some of the theoretical and practical aspects of probe measurements in a C02-laser discharge are discussed.

Variable reflectivity output coupler for improvement of the beam quality of a fast-axial flow CO2 laser

P. Sona, Peter F. Muys, Christophe Leys, et al.

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We present the design and performance analysis of a compact C02-laser, using a Variable Reflectivity Mirror (VRM) as output coupler and a positive branch confocal unstable resonator. High power together with good beam quality and compact design is demonstrated. The laser gas is excited by a DC-discharge.

Chemical gas-dynamic mixing CO2 laser pumped by the reactions between N2O and CO

Maxim Doroschenko, N. N. Kudriavtsev, A. M. Sukhov

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A study of populations inversion formation in a chemically pumped mixing shock driven CO2?GDLhas been conducted. ColdN2O injection was made in parallels into a hot flow with a chemical composition 25%CO + 25%He + 50%Ar by means of a central-body-type injector. The experiments were carried out with the coordinates of the in jeotion point 5 mm, 4 mm, 3 mm, 2 mm before critical section of a nozzle and 0.4 mm behind critical section. Diagnostics of the supersonio flow was performed by means of a gain for 10.6 ?m in CO2-laser transition, intensity of IR emission of C02 in a 4.3 ?n band and intensity of visible chemiluminescence CO + O ? CO2 + hv recordings. Prom the measured values of the gain and intensity of IR emission vibrational temperatures of the laser levels were determined. The largest values of the gain up to 0.7 m-1 were obtained when the injection was in a 3 mm before critical section. The gain was recorded in the experiments with the injection in a 0.4 mm behind critical section. Chemical reactions occurred in each experiment in which stagnation temperature behind reflected shockwave exceed 1700 K. Vibrational temperature of the upper laser level in the experiments with reacting mixture was f ound to be considerably exceeding that in the experiments with inert mixture with a composition conformed to a composition of reacting mixture after completion of chemical conversions. The exceeding monotonously increased from 500 K to 900 K when the injection coordinate changed from 5 mm before to 0.4 mm behind critical section. Analogous exceeding of the lower laser level temperature reached 300 K. A strong chemiluminiscence was detected in the experiments with reacting mixture. Thus , quasy—stationary chemical pumping of CO2 vibrat ions by reactions o N2O with CO occurred in the nozzle o GDL was firstly observed.

Output characteristics of a transverse-flow cw CO2 modular laser

P. Kukiello, Grazyna T. Rabczuk

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The design, construction and sons preliminary operational characteristics of a fast flow, closed cycle CO2 modular laser of the power up to 1 .5 kW which has been developed for industrial use are presented in the paper.

Beam quality in laser amplifiers

Rosario Martinez-Herrero, Pedro M. Mejias

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Using the thin-sheet bidimensional model, propagation of the beam quality of arbitrary multimode beams through laser amplifiers is analysed. An stochastic formalism based on the Wigner distribution function of the field is employed, and some general properties of the spatial characteristics of the beams are pointed out.

Development of the aerodynamic window for high-power CO laser

Shizuma Kuribayashi, Osama Noda, M. Ogino, et al.

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To develop an aerodynamic window for high-power CO lasers, we made a prototype of an air exhausting window. This prototype was consisted of four orifices and two vacuum pumps, and the optical axis coincided with gas flow direction. It was fixed to 5kW CO laser machine and the performance was tested. The result of experiments showed the good air exhausting property and the successful extraction of over 2kW CO laser beam.

Laser beam propagation through inhomogeneous amplifying media

Rosario Martinez-Herrero, Pedro M. Mejias

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A general analytical-numerical procedure has been established to calculate the amplitude of a laser beam propagating through an active amplifying medium, valid for arbitrary spatial inhomogeneities. The characteristic parameters representing the medium are small-signal gain, refractive index and saturation intensity.

Resonators for coaxial slow-flow CO2 lasers

Uwe Habich, Axel Bauer, Peter Loosen, et al.

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The design and performance of a coaxial slow-flow CO2 laser system is reported. Three types of resonators are tested with a rf-excited discharge with a maximum output capability of 800 W: a stable resonator with internal axicon, a multipass resonator with spherical folding mirrors (Herriott-cell) and a resonator with two toric mirrors.

Coupled CO2 lasers

V. V. Antyukhov, Alexander V. Bondarenko, Alexander F. Glova, et al.

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This paper is a review of experimental and theoretical results obtained at Branch of Kurchatov's Atomic Energy Institute to understand the possibility of development of high power laser systems on base of coupled C02 laser arrays.

Potential IF chemical laser

B. Leporcq, C. Verdier, F. Lemoine, et al.

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The electronic transition IF B3 ?(0+)--> IF X1?+ is accompanied by a radiative emission in the vicinity of 625 nm. The possibility of using this transition in a chemical laser through direct production of the B state is estimated. A computer code has been developed and applied to a kinetic scheme also described. It has been observed that a population inversion between IF B 3?(0+), v’=0 and IF X1?+ v"=5 can be achieved. IF B is obtained by mixing I (2 P 3/2) plus F (2 P 3/2) with O2 (1 ?). Atomic species are produced directly by only one combustion followed by frozen expansion. A set up is proposed to demonstrate the laser effect. The characteristic time of mixing and the population inversion lifetime are so close, that an optimization of the injection and mixing conditions is necessary. In a first experimental step to demonstrate laser effect, the iodine planar laser induced fluorescence technique allowing the visualization of mixing flows was used to qualify and to optimize the injection device.

Optical quality of a combined aerodynamic window

Keming Du, Joachim Franek, Peter Loosen, et al.

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The novel aerodynamic window with a pump cavity and a supersonic gas jet described in /1/ shows considerable improvements in operation performances such as shock-free operation range, reduction of the mass flow rate as well as operation stability. Its optical quality at different operation states has been investigated firstly with the schlieren method. Then the window was combined with a 5 kW CO2 laser using an unstable resonator. The influences of the window on the laser beam quality at different operation states have been investigated. The results will be presented in this paper.

CO2 coupled-mode, CO, and other lasers with supersonic cooling of gas mixture

Eugene M. Kudriavtsev

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There are presented in review results of physical investigation of GDL with heat— and electrical discharge pumping deals with extending of spectral region of laser emission as in IR as in ultraviolet and published after ~ 1980 (and so not included in 1).

High-power chemical oxygen-iodine laser

B. Barnault, Roger Barraud, L. Forestier, et al.

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A high power kilowatt class Chemical Oxygen Iodine Laser (COIL) has been developed at ONERA. In order to obtain a good quality I2-o2 mixing and reliable vapor iodine flow rate, a new iodine heater system has been studied and successfully tested. Optical diagnostics are used to measure iodine vapor, residual chlorine, water vapor concentrations and singlet oxygen flow rate. The set-up has now been completed and the new chemical oxygen generator is being tested. Preliminary tests have been performed with a reduced bubble column producing a laser output of 100 W for 50 s.

Gas flow effects in pulse avalanche discharge XeCl excimer laser

Qihong Lou

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The transverse gas flow excimer laser with x-ray and UV preionization were used to investigate the gas flow effects on the performance of XeCl laser. The density disturbances created by high input power density and nonuniformity of the gas velocity along the optical axis will reduce the laser power at high repetition rate.

N-substituted 1,8-naphthalimide derivatives as high-efficiency laser-dye: dependence of dye laser emission of protonated solvent

E. Martin, Antonio Martinez Pardo, J. M. L. Poyato, et al.

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Optimum condition for the lasing efficiency of four organic compound, as an active laser medium, excited by a Nytrogen pulsed laser (FWHM ? 5.7ns), has been investigated. The output energy was dependent on: solvent, dye concentration and for three of the compounds (II, III and IV), of protons concentration in the solvent used. We show lasing efficiencies in table I. According to the obtained results, we have specially discussed the importance of protons in photoinduced charge transfer process, in the compounds with an amino terminal group in the substituent R1.

Visual observation and numerical analysis on the reaction zone structure of a supersonic-flow CO chemical laser

Wataru Masuda

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The cavity flow field of a supersonic flow CO chemical laser is observed visually and then simulated numerically. The effects of the nozzle boundary layers, the cavity boundary layers and the mixing process on the laser performance are studied. The thin shear layer approximation is applied to the mixing region and the resulting equations are solved by the Crank-Nicolson predictor-corrector method. The numerical results show that the development of the mixing layer in the downstream direction is very gradual. The small signal gain coefficient begins to decay at a location where the mixing layer is still a small portion of the total flow width. The predicted distributions of the averaged gain along the flow agree fairly well with the experiment. It is clearly demonstrated that the presence of the boundary layers and the magnitude of the wall catalysis play decisive roles in determining the laser performance

Second harmonic generation of chemical oxygen-iodine laser

Fumio Matsuzaka, Kazushige Nigawara, Ken Terasawa, et al.

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Internal second harmonic generation of chemical oxygen iodine laser is studied. B8-BaB204 (BBO) is used as a conversion medium. A chemical oxygen iodine laser which have output of maximum 200 W (Multi mode operation) is used. Second harmonic power of 100 mW is obtained.

Optimization of discharge parameters of an e-beam sustained repetitively pulsed CO2 laser

Mark-Udo Beth, Thomas Hall, Wilhelm Mayerhofer

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Discharge parameters and load characteristics of a repetitively pulsed e-beam controlled CO2 laser (12 liter cavity) were investigated experimentally at different laser gas pressures up to 0.6 atm and electrical input pulse energies up to 2000 Joules. An electrical power modulator and optimization procedures are presented for matching conditions between power generator exit impedance and dynamic laser-cavity load with respect to efficient laser pulse shaping in the megawatt power range.

Resonant IR laser-induced diffusion of oxygen in silicon

M. V. Artsimovich, A. N. Baranov, V. V. Krivov, et al.

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The analysis of experimental data on resonant IR laser-induced diffusion of oxygen in silicon are presented in this work.Resonant irradiation leads to the increase of oxygen diffusion coefficient which corresponds to increase of effective temperature of the crystal approximately by three times. The control experiments included changing of laser emission wave length (10.6 and 5 mkm instead of 9.2 mkm) and turning of direction of electric vector oscillation of plane polarized laser light.

Cavityless dielectric-waveguide-mode generation in a weakly amplifying gaseous medium

Lev Yu. Mel'nikov, Viatcheslav A. Kochelap, Igor A. Izmailov

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In the paper a new method is proposed for direct transformation of electronic energy of metastable species in inverse medium into energy of waveguide modes localized in a dielectric waveguide. Different waveguide configuration are examined. Numerical calculations show that transformation efficiency can be as high as 15-20 %, allows to achieve a high level of utilization of solar energy in those spectral regions {~ 1.3 .?m) where light losses are minimal (0.2 dB/km).

Comparison of welding results with stable and unstable resonators

Joachim Franek, Keming Du, Silke Pflueger, et al.

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In order to compare welding performance of stable and unstable resonators an industrial axial-flow CO2 -laser in the 5 kW range has been operated with two stable and one unstable resonator at 5 kW. Along with a beam diagnostic analysis of the beam quality benchmark welding tests have been carried out. The results show, that for stable resonators the beam quality is a measure of the welding performance. However the unstable resonator shows considerable higher welding depth as predicted by beam quality dependency found for stable resonators.

Thermocapillary effects in a melted pool during laser surface treatment

D. Morvan, Francois Dominique Cipriani, Daniel Dufresne, et al.

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Laser surface treatment represents a promissing new technology for materials processing. The main advantage of lasers is constituted by the facility to deposite high density energy at the surface of a material which permits to obtain a narrow heat affected zone and low distortion. During the surface melting of a material, the heat flow in the melted pool is dominated by convective effects. The temperature gradient on the melted pool surface between the laser beam impact point and the pool boundary generates surface tension gradient and therefore a surface tangential strain which produces convective motions (Marangoni convection). In this paper we presents a numerical model of the thermocapillary flow in a melted pool created by a scanning CW laser. We analyse the effects of experimental conditions as scanning velocity and beam dimension upon the intensity of the thermocapillary flow, the dimensions and the shape of the melted zone.

High-power electron beam controlled discharge N2O laser

K. Frolov, Andrei A. Ionin, M. Kelner, et al.

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High power pulsed electron beam controlled discharge (EBCD) N2O laser (?, ~ 10.9 (?m) has been created. The influence of the molecular (N2 ,CO) and atomic ( He, Ar, Xe ) gases addition to the laser mixture on the energy characteristics has been studied experimentally. The laser energy (more than 102 J) was two orders of magnitude higher than that known for pulsed electric discharge N2O lasers.

High-average power XeCl laser with surface corona-discharge preionization

Haruhiko Nagai, Kenyu Haruta, Yukio Sato, et al.

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A new combination of a surface corona-discharge preionization (SCP) electrode with a spiker-sustainer circuit is investigated for the development of a high-average power XeCl excimer laser with high repetition rate. The investigation for single shot operation proves the potentialities of the combination scheme. The result of repetitive operation demonstrates the promising prospect as an excitation scheme of industrial high-power excimer 1aser.

Long-time operation of a 5kW cw CO laser

Osama Noda, Shizuma Kuribayashi, Shigenori Imatake, et al.

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Investigation ofgas composition for a 5kW electric discharge cw CO laser was made to achievelong time operation. This device is a closed-cycle self-sustained discharge-excited cw CO laser with subsonic gas flow. Recirculating gas is cooled through heat exchangers operating with liquid N2. Under typical operating conditions, the laser is operated with a continuous fresh laser gas supply and a part of recirculating gas is exhausted to control operating pressure. As a result of removing contamination, especially CO2 gas, by the cold trap, continuous operation for more than 12 hours has been achieved at a power level of 5kW, with electrical conversion efficiency of 24%. Moreover, dependences of CO2 conceniration in the mixture on cathode materials were measured with a gas chromatograph. It has been revealed that the CO2 concentrations can be reduced to about a half by using the Molybdenum alloy or Tungsten alloy cathodes, when compared with the Copper ones.

Estimation of CO2/N2 mixing region by the small-signal gain measurement

Hiroshi Ohue, Eiji Kasahara, Kamon Uemura, et al.

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For the estimation of COzs/N2 mixing region on after-mixing C02 gasdynamic laser, the small-signal gain distributions were measured at different pressure ratios at the nozzle exit. In this study, a shock tube was used and the shock-free nozzle and the wedge nozzle were employed. From these experiments, we found that the small-signal gain distribution is considerably dependent on the pressure ratio at the nozzle exit, whereas only a small difference was seen between the two nozzles.

Supersonic electron beam controlled discharge CO laser

Andrei A. Ionin, Andrei A. Kotkov, M. G. Minkovsky, et al.

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An electron-beam controlled discharge (EBCD) supersonic CO-laser operating at transient conditions of excitation (?dis /?tr~1) has been investigated. Mach number equaled 3.0. The e-beam current density was 1 mA/cm2 . The discharge has been excited between two electrodes spaced 41 mm. The axis of the main resonator has been shifted from the discharge region centre by 120 mm downstream. Small additions of H2 (1-2%) into CO:N2: Ar gas mixture resulted in the increase of a specific input energy, but the efficiency has been reduced. Maximum efficiency reached 20 % . The output peak power has been gradually growing with the growth of the gas density,and reached 90 kW ( the gas density being 0.5 Amagat ). Five additional cavities have been placed downstream. The usage of the cavities has allowed us to measure the lifetime of the inverse population in CO:N2: Ar mixtures.

Mechanical effects induced by high-power HF laser pulses on different materials under normal atmospheric conditions

Sylvie Paolacci, Manfred Hugenschmidt, Philippe Bournot

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Experiments were performed to measure mechanical pressures and total momenta imparted by pulsed HF laser radiation on different materials (aluminum AU4G, graphite 5890) under normal atmospheric conditions at peak power densities ranging from 107 W/cm2 to 8.107 W/cm2. The dynamical pressure measurements were obtained at the rear side of the targets by using piezoelectric PVDF gauges and by a ballistic pendulum as well for determining the mechanical coupling coefficients. Pressures of more than 100 bars and mechanical coupling coefficients up to 6 dyne.s/J were observed that were strongly depending on the type of material and upon the focussing conditions. Experimental data are compared with theorical models. These experiments revealed that at these peak power densities the mechanical effects were mainly induced by the propagation of laser supported absorption waves

Measurement of the gain in a XeF (C-A) laser pumped by a coaxial e-beam

H. M. J. Bastiaens, Peter J. M. Peters, Wilhelmus J. Witteman

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Abstract not available.

Population of high-vibrational levels of the iodine ground state in its dissociation process by singlet oxygen

B. Barnault, V. Joly, Daniel R. Pigache

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The dissociation of I by 02 in a Chemical Oxygen Iodine Laser (COIL) cannot occur with a single colision. A two-step model where the excited intermediate species is identified with the vibrational states of 12x(0+g), with V between 30 and 43, has been proposed. The existence of these species has already been checked by using laser fluorescence excitation spectroscopy. The improvements of this experiment will permit one to make absolute measurements of the iodine vibrational level populations along the reaction zone and to know excitation rates of I2 by O21 •

Pulsed CO2 laser-material interaction: mechanical coupling and reflected and scattered radiation

Prat Christophe, Michel L. Autric, Georges Inglesakis, et al.

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In general, high-intensity laser radiation causes heating, fusion and then vaporization of the target material. The vapor thus produced then interacts with incident radiation and becomes ionized, forming a more or less absorbant plasma which modifies the coupling with the material. At the start of interaction and during it, however, a fraction of the incident energy is reflected and scattered by the target and the plasma. The mass which is ejected with a high speed, and the expansion of the vapor, lead to the formation of a shock wave and mechanical impulse on the target. The variety of laser characteristics and experimental conditions sometimes makes it difficult to compare the results of measurements. This difficulty is even greater when different types of measurement are brought together. The second part of this article explains the results of measurements of mechanical and thermal coupling, as well as those of the energy reflected and scattered by the test sample and plasma, under the conditions presented in the first part.

Kinetics and yield of Xe excitation as third body in the process of N(4S) atom recombination

U. V. Ivanov, A. M. Pravilov, L. G. Smirnova, et al.

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Kinetics of Xe excitation in active nitrogen was stndied using XeCl* formation in reaction Xe* +Cl2(CCl4) as a monitor of Xe{6s} states. It was found out that Xe excitation involves energy transfer from N2* molecules formed in three body recombination. (M) N(4S) + N(4S) + Xe > N2(X,V) + Xe*({6s},{6s,},{6p})Excitation of Xe{6s} states shows termolecular kinetics with rate constants for M = He, Ar and Xe carriers respectively: 0.41 10-33, 0.86 10-33 and 1.10-33 in cm6/s, at room temperature. Thus the studied system manifests itself as having high quantum yield for conversion of chemical energy, released in the act of recombination into energy of excited Xe atoms or excimers.

Study of the production of S2(B) from the recombination of sulfur atoms

Pascale Prigent, Henri Brunet

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Chemiluminescence emitted during the recombination of ground state S atoms was studied in the aim of obtaining a laser emission on the B-X electronic transition of the sulfur molecule. S atoms were produced by reaction of fluorine atoms with hydrogen sulphide in a supersonic expansion. F atoms were produced in a combustor from the reaction of excess NF3 and H2 with He diluent at pressures from 1.3 to 3 atm. Chemiluminescence was observed in the supersonic flow at pressures ranging from 20 to 70 Torr. Experimental spectra were compared to synthetic ones. At a pressure of 70 Torr, a population density of S2(B) close to 108 molecules/cm3 was determined by chemiluminescence intensity measurements. This value is in reasonable agreement with that predicted by our kinetics modeling.

Visible and UV gas lasers with high-current radiative discharges excitation

A. S. Kamrukov, Nicolay P. Kozlov, Yuri S. Protasov

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It is a brief review of studies of lasing and energy-spectral characteristics of gas lasers utilizing - the excimer-like mercury halide vapor HgX2 (X=C1, Br, I), inert gas halogenides - XeF (B-X), (C-A) and molecules of the stable halogens (I2, Br2), optically pumped by wide-band UV-VUV radiation of high-current radiative discharges.

Red emitter resulting from O2 (a1 delta g): a new lasing species?

Qi Zhuang, Tieji Cui, X. B. Xie, et al.

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In 1989, Yoshida et al. first reported on the occurrence of an unexpected intense red emission in low pressure O2 (a1?g). They believe that the new compound formed is O*4 In this paper, besides reporting on the action of various metal catalysts on the red emitter formation, we will present evidence for the indispensable role of chlorine in the red emitter formation.

The EU 194 project: industrial applications of high-power CO2 cw lasers

A. Quenzer, Eckhard Beyer, Jose M. Orza, et al.

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We describe the aims and some results obtained in EU 194 program and his special place among the EUROLASER issued EUREKA projects. The project management with a Steering Committee, working groups on basic problems and workshops on different application themes are explained. Their interaction with other European projects and organizations are pointed out fra* problems so as standardization and safety.

Multipass unstable negative branch resonator with a spatial filter for a transverse-flow CO2 laser

Grazyna T. Rabczuk

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In order to specify the operation characteristics of a transverse-flow cw CO2 laser employing a negative branch unstable resonator with an internal field limiting aperture (self-filtering unstable resonator - SFUR); diffraction type analysis providing mode distributions and power extraction has been made with taking into account the nonlinear medium gain influence on the resonator properties.

Plasma motion velocity along laser beam and continuous optical discharge in gas flow

A. P. Budnik, K. G. Gus'kov, Yuri P. Raizer, et al.

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Solving the problem of gas flow around hollow ball it is shown why the velocity of laser deflagration wave is an order higher than velocity of wave driven due to heat conductivity. Analitical theory is confirmed by numerical solution and the results are in satisfactory agreement with experimental data.

Assessment of a discharge-excited supersonic free jet as a laser medium

Fumihiko Kannari, F. Sato, Minoru Obara

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Experimental results of spectroscopic measurement of spontaneous emission from argon gas excited electrically in a nozzle discharge followed by supersonic expansion are described. A strong line emission at 152.6 nm originating from Si(ll) 4s-3p is observed together with relatively weak emission line around 126 nm. A theoretical model that takes account of collisional gas kinetics, discharge processes, and empirical treatment of the free jet expansion is developed to examine the capability of the discharge excited gas as a laser medium for Ar2 excimer at 126 nm wavelength.

Studies of short-wavelength chemical lasers: enhanced emission of Pb atoms following detonation of lead azide via a supersonic nozzle

Illana Bar, T. Ben-Porat, Ari Cohen-Nov, et al.

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Previous studies in our laboratory have shown that preferential excitation of high lying electronic states of the lead atom is obtained following the detonation of lead azide. However, measurements have shown that the detonation products form an optically opaque medium. In order to overcome this problem, the detonation was conducted via a supersonic nozzle. As a result a transparent medium was formed near the nozzle exit plane. Strong emission from lead atoms was achieved in this medium. Time- and wavelength resolved measurements have shown that the emission intensity of the 3P1° ? 1 D2 transition of the lead atom is significantly enhanced as compared to that from 3P1° to lower lying states. The behavior of the emission is explained in terms of kinetic and spectroscopic (self-trapping) mechanisms. The implication of our results to obtaining laser oscillation following detonation via supersonic nozzles is discussed.

Laser surface treatment: numerical simulation of thermocapillary flows

Agnes Roux, Francois Dominique Cipriani

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This paper is devoted to the numerical simulation of thermocapillary flows occuring in laser surface treatment. A two dimensionnal rectangular cavity is used to model the molten pool which occurs when a laser beam impinges a material. The simulated free surface, considered flat or deformable, is subjected to a sinusoidal temperature distribution. Motion equations are solved by a finite element method. Effects of dimensionless parameters on the convection in the melt are shown.

Numerical simulation of the combustion chamber of a chemical laser

E. Saatdjian, J. P. Caressa, Jean-Claude Andre

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The hydrodynamics in the combustion chamber of a chemical laser has been simulated numerically using a vorticity ? - stream function ? formulation. The flow is similar to that in a cavity when the fluid enters via only one injector and exits through only one tube. A large circulating vortex is formed ; its size depends on the chamber geometry and on the Reynolds number. Both a second order and a fourth order formulation have been used to solve the model equations ; the latter gives more accurate results for low Reynolds numbers but the former converges for a wider range of conditions. Comparison with experimental data has confirmed the validity of the obtained results.

Luminescence and ionization of krypton by multiphotonic excitation near the 3P1 resonant state

M. Saissac, P. Berejny, Philippe Millet, et al.

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We have developed, since several years, an experiment for the selective excitation of the heaviest rare gases (Xenon 1,2 and Krypton3) using a nitrogen pulsed dye laser. Recently, we made a spectroscopic and temporal study of the Krypton3 luminescence induced by the laser beam in the pressure range 0.03 to 500 Torr. The two V.U.V. continua (128 nm and 145 nm) of this gas can be detected when the laser wavelength is tuned between 365 nm and 371 nm

Free propagation of high-order moments of laser beam intensity distribution

Miguel A. Sanchez, Jose Luis Hernandez Neira, J. Delgado, et al.

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Free propagation of intensity distribution high order moments, for general multimode laser beams, has been studied. Simple analytical expressions, giving account for that propagation have been obtained, using the Wigner distribution function properties (WDF). Some properties have been derived

Transient gain phenomena and gain enhancement in a fast-axial flow CO2 laser amplifier

Heihachi Sato, Eiichi Tsuchida, Koichi Kasuya

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The transient gain phenomena observed in a fast-axial flow CO2 laser amplifier are theoretically explained by taking into account a gas temperature T and an inverted population ratio n2/n1 as a function of discharge time. Expressing the transient gain as a function of the gas-flow velocity v and the discharge current Idis including their spatial distribution along the radial direction of a plasma tube , both the transient power-decrease jP and transient time required to be a stable value are formulated with respect to a plasma length tst and an input probe power P , being well consistent with the corresponding experiments . Possibilities of improving these transient behavior are also demonstrated by cooling a plasmatube wall and a gold catalyst.

Modeling of high-power laser welding

Dieter Schuoecker

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Deep penentration laser welding is one of the most important applications of high power lasers, because it allows fast welding with high quality and minimum heat input and residual stress, even of difficult materials or material pairs. Modelling of this process is an important task, since it gives a deeper insight

Spatial characterization of high-power multimode laser beams

Julio Serna, Rosario Martinez-Herrero, Pedro M. Mejias

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New parameters are proposed which characterize arbitrary multimode tridimensional laser beams propagating through ABCD optical systems. Such definitions are shown to be related with the bidimensional concept of beam quality. Dependence on the propagation distance and coherence properties of the input field is illustrated by means of some examples.

Advanced matrix optics and its incidence in laser optics

Shaomin Wang, Eusebio Bernabeu, Javier Alda

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Propagation, transformation and self-consistent solution of laser beams could be treated by advanced matrix methods clearly, e.g.: misaligned laser systems are analyzed by augmented 4x4 matrix, phase conjugate mirrors are described by matrices with variable elements, nonsymmetrical laser systems are treated by tensor ABCD law, optical arrays are performed as pseudo-conjugators, a new Fresnel number for Gaussian beams is defined and finally, hard aperture is written in terms of matrix and so, all the transformation of laser beams has to be reconsidered.

Tutorial on x-ray lasers

William T. Silfvast

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The fundamental principles of x-ray lasers are discussed. Topics such as inversion density requirements, gain saturation, plasma production, excitation mechanisms (including electron excitation, photoionization and recombination), electron density limitations and laser mirror properties are described. Various laser systems including quasi-steady-state lasers and transient, non-equilibrium photoionization-pumped lasers are summarized.

Arc heater for thermal driven HF/DF chemical laser

Andre Sontag, Jean-Marie Baronnet

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A new concept of plasma heater has been developed using water vapor as plasma gas (1). It also operates with sulfur-hexafluoride diluted with nitrogen and oxygen; it makes it possible to use it as an F-atoms generator for an arc heated supersonic diffusion HF/DF laser. The fluorine atoms are created by dissociation of SF6 injected directly into the arc heater with argon, nitrogen and oxygen as diluents. As compared with the well known arc heater (2) in which the fluorinatcd gas is mixed in an arc heated helium flow, a higher dissociation rate of this gas is obtained. The arc heater is powered by a rectifier of 500 V and 250 A. For an electrical input power of 80 kW, we obtain a thermal efficiency of above 80 % and a specific enthalpy, at the output of the arc heater, of 8.3 MJ/kg. The described F-atoms generator will be equipped in the near future with an axisymmetric nozzle array, in order to complete the entire HF/DF laser device.

Surface absorptance in CO2 laser steel processing

L. Covelli, I. de Iorio, V. Tagliaferri

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To increase the absorptance of metal surfaces at the radiation of a CO2 laser beam in this work, a chemical etching technique has been used that allows the controlled modification of the superficial roughness. Absorptance tests have been performed in conditions close to real treatment using a CO2 c.w. 2.5 kW laser. The modification of the absorptance has been evaluated by means of the obtained effects on the treated surfaces. The achieved results show how the formation of microcavities on the analyzed surfaces allows a remarkable increase in the absorptance in real treatment conditions.

Flowfield in a CO2-N2 gas-dynamics laser with staggered nozzles

D. Tarabelli, David Zeitoun, Michel P. Imbert

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The flowfield of a CO2-N2 mixing gasdynamic laser is numerically analysed by using the laminar, two-dimensional unsteady Navier-Stokes equations coupled with the appropriate relaxation equations describing the vibrational transfer between the internal modes. These equations result from an averaging through the third dimension in order to take into account the area increase of the laser cavity in this direction. The equation system is solved with an explicit, time dependent, second order finite difference technique. The flowfield in each nozzle where CO2 and N2 are premixed and in the main laser cavity are so described. The analysis shows the complex structure of the flowfield, the influence of the premixing zone and of the diverging section on the small-signal gain coefficients and on the evolution of the flow quantities and the effect of different expressions of the transport coefficients on the vibrational energy distribution.

Advanced concepts of electron-beam-pumped excimer lasers

Frank K. Tittel, P. Canarelli, C. Brent Dane, et al.

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The development of scalable high power lasers in the UV-visible range and ultrashort high brightness laser sources will have significant impact in a number of key technologies. Experiments of scaling the e-beam pumped XeF(C—>A) laser system to the 1 Joule/pulse output level at a 1 Hz repetition rate are described. Recent progress in the amplification of tunable ultrashort laser pulses in the visible spectrum, utilizing the broadband XeF(C—>A) excimer transition, is also reported.

Discharge studies with a high-efficiency XeCl excimer laser

M. Trentelman, G. B. Ekelmans, Frederik A. van Goor, et al.

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Results on a high efficiency excimer laser operating according to the prepulse-mainpulsetechnique are reported. The laser volume of about 90 cm3 is X-ray preionized. The mainpulse obtained from a PFN is switched onto the discharge by means of a racetrack saturable inductor (magnetic switching)connected to the laser head with low inductance. Laser output energy has been measured as a function of gas mixture and delay between X-ray and prepulse.

High-repetition-rate x-ray preionization source

Frederik A. van Goor

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A high repetition rate X-ray source for preionization of high-pressure self sustained laser discharges has been studied. Use has been made of a corona plasma cathode and a water cooled reflective target. A dosage of 18mRad per pulse and per joule of input energy at a repetition rate of 300Hz continuously and 1kHz burst could be obtained. A rise time of the X-ray power of 13ns has been observed.

Time-space resolved optical study of the plasma produced by laser ablation of Ge: the role of oxygen pressure

Fidel Vega, J. Solis, Carmen N. Afonso Rodriguez

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Time and space resolved optical measurements of the laser induced plasma emission have been performed during the growth of Ge films in vacuum (105 mbar) and in an oxygen partial pressure up to 103 mbar. From these irteasurements,the tiite of flight spatial distribution of the plasma species as well as their average velocity is stablished. The velocity is found to be 3x106 cm/s and is not influenced by the presence of oxygen in the studied pressures interval. The lack of differences in the plasma behavior when ablation takes place in vacuum or in oxygen pressure is consistent with the low oxygen content found in the films.

Mixing diagnostic in a cw DF chemical laser operating at high-cavity pressure

Francois Voignier, Frederic Merat, Henri Brunet

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In order to increase the mixing rate by stretching the interface between reactant streams, we have developed gas trip nozzles and new supersonic nozzle designs (called ramp nozzle and deflector nozzle). Unlike trip nozzles which use inert gas injection to stretch the reactant surface, the ramp or deflector nozzle is believed to cause a similar effect through its geometry without gas injection. In this paper we report results of experimental investigation of the gain in a deuterium fluoride combustion driven chemical-laser operating at high cavity pressure (P > 15 Torr). Comparison of the small signal gain profile, observed along the gas flow direction, indicates appreciable differences between trip, ramp and deflector nozzles. At cavity pressure of about 15 Torr a peak gain value of 7 %/cm has been measured with the trip nozzles, the gain being positive up to 30 mm from the nozzle exit plan. The gain caracteristics of the laser with the trip jet flow on are quite different from those when the trip jets are off (laminar mixing). In this latter case the gain is only 1.5 %/cm. With ramp and deflector nozzles, shorter gain regions extended over only 20 mm were observed.

Fluctuation variation of a CO2 laser pulse intensity during its interaction with a cloud

R. Kh. Almaev, L. P. Semenov, A. G. Slesarev, et al.

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The intensity fluctuation variances of a CO2-laser radiation pulse in the course of its non-lenear propagation through a cloud are theoretically studied. Considered are the cases of regular and explosive clearing processes. It Is found that the initial intensity fluctuations can be noticeably intensified as a result of radiation self- action occurrence.

Highly conductive amorphous-ferrite formed by excimer laser material processing

Shigeru Kashiwabara, Kazuhiro Watanabe, Ryozo Fujimoto

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Laser material processing is one of the promising application fields of high power lasers which are being well developed as a sophisticated machining tool as well as conventional E-beam sources. Particularly, the UV photon material processing by excimer lasers have brought us unique and characteristic results on the processing capability to most materials because of high energy quanta of UV photons extending approximately from 190 nm to 350 nm. The high intensity UV photons would ablate and decompose materials largely due to photochemical processes rather than thermal effects

Characteristics of a compact 12 kW transverse-flow CO2 laser with rf-excitation

Eberhard Wildermuth, B. Walz, K. Wessel, et al.

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Design, sealed-off operation and optical properties of a 12 kW transverse flow C02-laser with rf-excitation are discussed. The design is characterized by transverse gas flow, rf-excitation, an unstable double pass resonator and an integrated catalyst. The sealed-off-operation is investigated by measuring the CO- and NO-concentrations and the small signal gain as functions of the operating time. The optical properties, determined by the compensation of the density gradient in flow direction which is inherent to transverse flow lasers, are investigated in several experiments.

Discharge technology for excimer lasers of high-average power

Wilhelmus J. Witteman, G. B. Ekelmans, M. Trentelman, et al.

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The self-sustained discharge of excimers is analyzed. Several excitation schemes that have been successfully applied are compared. For high repetition rate operation not only the discharge stability and its efficiency are important selection criteria but more important is the potential of fast discharge switching with minimum pulse energy. Pulse compression plays a key role in the laser performance. A technology for low energy compression is described.

New construction of sealed-off CO2 laser

Wieslaw L. Wolinski, Radoslaw Wolski, Karol A. Janulewicz

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New construction of d.c . sealed-off CO2 laser is presented . The sealed-off Laser has been improved. by employing gas ballast and free gas exchange from the gas ballast to the discharge volume along the discharge column. In this construction approximately the same level of output power for sealed—off and slow flow conditions was obtained.

Performance of CO2 and CO diffusively cooled rf-excited strip-line lasers with different electrode materials and gas composition

Shaul Yatsiv, Amnon Gabay, Baruch Sterman, et al.

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Strip-line molecular lasers with a narrow gas sheath confined by bare metal electrodes are sensitive to chemical processes that influence the gas composition during the RF discharge. Both CO2 and CO gas mixtures in a stationary gas in the discharge reach a steady state composition, and an associated asymptotic laser performance is attained. However, the process of CO2 dissociation has the opposite effect on the gas composition than CO + O recombination or 2CO ?CO2 + C disproportionation reaction. Therefore, materials like gold, that catalyze the CO2 formation, exhibit complementary behavior with respect to power decline in sealed off CO2 versus CO laser operations. We describe the operation of a RF excited strip-line CO gas laser at a cooling temperature of 0°C. The laser power and efficiency are critically dependent on the purity of the constituent gases and on the nature of the electrode metal. Changes in the laser power and efficiency during the discharge are correlated with measurements of changes in the gas constitution monitored mass spectrometrically. A solid powder (definitely not carbon soot) which has a deleterious effect on the laser performance was observed. Following Bhaumik et al, mercury vapor was introduced into the gas mixture in a conventional DC excited Pyrex tube. An improvement of better than 40% in the power and efficiency as well as changes in the spectral distribution of a CO laser were observed.

High-power chemical oxygen-iodine lasers and applications

S. Yoshida, Kouki Shimizu

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The chemical oxygen iodine laser is no longer a research tool but is now entering the application stage. Because of its unique properties, the laser has potential for a lot of new applications. This paper summarizes the current status of the technology and research on the laser. Particular emphasis is given to the feasibility of industrial applications.

Performance characteristics of premixing gas-dynamic laser utilizing liquid C6H6 and liquid N2O

T. Yokozawa, Hayato Nakajima, Shigeru Yamaguchi, et al.

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A gasdynamic laser of premixing type fueled with benzene (C6H6) and nitrous oxide (N2O) was developed, using which the small-signal gain characteristics were studied. Also, comparisons of performance were made between nozzles of two-dimensional type and of three-dimensional screen type. With two-dimensional nozzle, the small-signal gain proved to rise sensitively with increasing combustion temperature, to reach 0.65 m-1 at 2,400 K. With screen nozzle, the temperature dependence of small-signal gain was similar in trend. The level of small-signal gain, however, proved to be roughly 0.3 m-1 higher with two-dimensional than with screen nozzle.

Pulsed chemical oxygen-iodine laser

Nikolai N. Yuryshev

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The features of the pulsed chemical oxygen-iodine laser operation are discussed. It is noted that alkyliodides are preferable iodine donors in the case of the chlorineless mixture of RI and singlet oxygen. The fast deactivation of the singlet oxygen by RO2 is a limiting factor when perfluoroalkyliodides are used as iodine donors.

Effect of acoustic dampers on the excimer laser flow

David Zeitoun, D. Tarabelli, Bernard M. Forestier, et al.

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It is well-known that to obtain a good quality laser beam in high repetitive rate excimer lasers, the acoustic waves due to a non uniform energy deposition between the electrodes, must be strongly damped. The unsteady two dimensional flow in eximer laser cavity has been described previously 1 by a numerical approach. The aim of this paper is to include in the numerical code a modelization of the sidewall mufflers in order to study the influence of the porous material on the behaviour of transverse and longitudinal waves in the excimer laser cavity. In the muffler, the flow is assumed one dimensional (y direction) and is coupled to the laser cavity flow. These flows are described by Euler equations and the numerical method is based on an explicit difference scheme assiociated with a corrected transport algorithm (Shasta method)2. The results show the propagation and the damping of longitudinal shock-waves and acoustic waves for different kind of mufflers. Different shapes of laser cavity are also investigated to study the influence of the electrode raduis curvature on the transverse waves. These results are compared to experimental results obtained from the L.U.X. laser of Institut de Mecanique des Fluides de Marseille.

High-gain tunable laser medium: XeF-doped Ar crystals

Gerald Zerza, R. Kometer, Gerard Sliwinski, et al.

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Small signal gain coefficients are derived from XeF concentrations, absolute emission intensities, line narrowing of amplified spontaneous emission and from amplification measurements on the D—X (286 nm), B—X (411 nm) and C—A (536 nm) transitions. The gain values of the order of 10 to 30 cm-1 for rather low pump energies and the large spectral range can be interesting for ps applications.

Gas-dynamically cooled CO laser with rf-excitation: optical performance

Eberhard Zeyfang, Hartwig von Buelow, M. Stoehr

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After achieving steady long term operation of the rf-excited COlaser, the output beam has been examined for different resonator geometries. Results of near- and farfield beam profile measurements are reported for multipass stable resonators. The experimental results concerning focus diameter and intensity profile are compared with theoretical calculations. Furtheron the power distribution of the different spectral lines of the CO-laser, fluctuations of single lines and of the overall output power have been investigated. A pulse mode operation of the CO-laser can be realized very easily by the rf-excitation.

Kinetics and electrical modeling of a long-pulse high-efficiency XeCl laser with double discharge and fast magnetic switch

M. Boyomo Ngo Kobhio, Bernard L. Fontaine, Jean-Marc Hueber, et al.

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A complete model of the long pulse XeCI excimer laser excited by a double discharge with fast magnetic switch has been established for an Ne/Xe/HCI active medium. This model simulate one of the potential working conditions of the IMFM high average power LUX test-bed. Model includes rate equations for species with most recent availiable rate constant values, circuit equations with time dependant ferite switch inductance and plasma impedance and rate equation for laser emission taking into account absorptions. The model allows to simulate very long laser pulses (150-200 ns) and numerical results are in good agreement (within 30 %) with experimental results obtained at IMFM.

Spectroscopic determination of the parameters of an iron plasma produced by a CO2 laser

Angel M. de Frutos Baraja, Lilian Sabatier, Anne Poueyo-Verwaerde, et al.

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During the process of metal welding by continuos CO2 laser, a plasma of the metallic elements is formed. In order to improve the procedure it is necesary to characteryze this plasma. We have carried out spectroscopic measurement of both temperature and electronic density. Our target was iron, and only iron lines could be identified in all our experiments. So, we were forced to use only iron lines for the plasma diagnostic. Our results show the distribution, along more of 20 mm from the target surface, of a plasma which has at its maximum a temperature of 6300 K and an electronic density of 9x1016 cm-3.

Two-dimensional computer modeling of discharge-excited CO gas flow

Mitsuhiro Iyoda, Tomoya Murota, Mamoru Akiyama, et al.

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In order to simulate and predict the complex mechanism of the high power CO laser excited by transverse dc discharge, a two-dimensional gas flow model has been developed from the authors' one-dimensional model. Based on the control volume method for two-dimensional Cartesian coordinates, the fundamental equations deal with state, continuity, momentum, energy, and reactions. The similar discharge power distribution can be given as the experiment, where the power density is higher around the hollow-cathode array than around the plane anode. Although the speed of the CO gas mixture is in the sub-sonic region, the effect of compression is taken into account. The integration is repeated by SIMPLEST method and the matrices are solved by MICCG method for the pressure equation and by MILUCR method for the other equations. The computation is carried out by a HITAC S820 supercomputer and a Sun-4 workstation. As a result of the simulation, non-uniform distribution of the gas parameters was made clear.

Precise uncoupling theory to study gain of gas-dynamic laser

A. R. Bahram-pour, Esmail Mehdizadeh, M. A. Bolorizadeh, et al.

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A variable quasi specific heat ratio along the supersonic nozzle of a gasdynamic laser (GDL) is introduced as a sequence. This simplifies the energy equation of the expanding gas and reduces it to a linear first order differential equation. By introducing an L2 metric on the induced gain sequence g(n) , it was observed that the sequences converge on the first step quickly. Furthermore, this precise method requires less computation time compared with the other methods.

Numerical modeling of laser-matter interaction in high-intensity laser applications

Jose Luis Ocana

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Traditionally, the application of laser beams to the processing of material workpieces has been restricted to relatively low intensity regines, mainly because of the linited power of the available laser sources and the potentially bad laser-matter coupling properties introduced by the weak plasna generated at sonewhat higher intensity regimes (I>10 W/cm2).

Excimer and nitrogen lasers with low-average power for technology applications

Ludwik Jerzy Pokora

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For the last few years applications of excimer lasers in technological processes aroused more and more interest. It is due to many unique UV radiation parameters of those lasers. The most important of the parameters are: ability of focusing on very small area, low diffraction in lithographic processes, non-thermal (cold) nature of interreaction with materials, significant absorptivity for most of metals.

Multimode laser beams behaviour through variable reflectivity mirrors

Miguel A. Porras, Javier Alda, Eusebio Bernabeu

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In this work, laser resonators with variable reflectivity mirrors are studied by applying an alternative matrix method. It provides a clear and fast tool to analyze the effects of real (apertured) optical systems on multimode laser beams.

Multikilowatt transverse-flow CO2 laser with variable reflectivity mirrors

Laura Serri, C. Maggi, Luciano Garifo, et al.

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A gaussian reflectivity mirror has been used as output coupler of a positive branch confocal unstable resonator in a multikilowatt transverse flow DC excited C02 laser source. 1 kW output power and a radiance value comparable with those of fast axial flow lasers at the same power level have been obtained.

Thermal regulation applied to CO2 laser self-quenching of complex geometry workpieces

F. Bataille, Didier Kechemair, C. Pawlovski, et al.

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Real time control during multikilowatt CO2 laser surface treatments is required to improve reproducibility, to simplify applications to complex geometry workpieces and to deal with every kind of unsteady situations. An automatic strategy was chosen, using linearization around current points to solve non linear problems. Application to laser self quenching is then detailed, experimental setup and complete closed loop are described. Experimental results of the closed loop are finally exposed. Regulation robustness using power or speed command is show against geometrical perturbations. Another regulator was applied to insure temperature cycles to non moving 10x10x1 mm3 samples in controlled atmosphere chamber during titanium nitriding studies.

Thomson scattering diagnostics of discharge plasmas in an excimer laser

H. Yamakoshi, Motoko Kato, Y. Kubo, et al.

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The electron-velocity distribution function of the discharge plasma in a rare gas halide excimer laser was diagnosed by the Thomson scattering method. The measured electron-velocity distribution function shows that the predicted value by the calculation is accurate. Those results assure that the calculation method which is based on the kinetic calculation using the circuit equations, the Boltzmann equation and the rate equations is effective in the excimer laser simulation.

8th Intl Symp on Gas Flow and Chemical Lasers

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Table of Contents