Laser research at the Institute of Physics of the Academy of Sciences of Czech Republic covers both the development of advanced pulsed high-power laser systems, the iodine and x-ray in particular, and their applications in science and technology. The COIL laboratory with a small chemical oxygen-iodine laser facility participates in the worldwide effort to develop a competitive quasi-steady laser device for industrial and military applications. In the new laboratory SOFIA a unique hybrid laser system consisting of a commercial crystal oscillator and iodine power amplifiers (SOFIA = Solid State Oscillator Followed by Iodine Amplifiers) has been developed. It is used as a pump of parametric amplifiers in a pilot OPCPA experiment. Our largest laboratory, the PALS Research Centre operated jointly with the Institute of Plasma Physics AS CR, is open to external users, offering them the beam time of the TW/ns iodine laser system PALS (Prague Asterix Laser System). Several tens of experimental projects have been performed at PALS since September 2000, aimed e.g. at various applications of plasma XUV sources, QSS plasma XUV lasers, laser ion sources, and laser-induced shock waves. An overview of the research programmes of all the three laboratories is given in the paper.

Four major types of laser sources are used for material processing. Excluding Excimer lasers, this paper focuses on advances in High Power CO₂ lasers, Solid State Lasers and Diode Lasers. Because of their unrivaled cost to brightness relationship the fast axial flow CO₂ laser remains unrivaled for flat-sheet laser cutting. Adding approximately a kW of output power ever four years, this laser type has been propelling the entire sheet metal fabrication industry for the last two decades. Very robust, diffusion cooled annular discharge CO₂ lasers with 2kW output power have enabled robot mounted lasers for 3D applications. Solid State Lasers are chosen mainly because of the option of fiber delivery. Industrial applications still rely on lamp-pumped Nd:YAG lasers with guaranteed output powers of 4.5 kW at the workpiece. The introduction of the diode pumped Thin Disc Laser 4.5 kW laser enables new applications such as the Programmable Focus Optics. Pumping the Thin Disc Laser requires highly reliable High Power Diode Lasers. The necessary reliability can only be achieved in a modern, automated semiconductor manufacturing facility. For Diode Lasers, electro-optical efficiencies above 65% are as important as the passivation of the facets to avoid Burn-In power degradation.

Providing highest energy efficiency and best optical quality COIL is still remaining today the most perspective source of high power radiation for practical uses. Expansion of such lasers applications depends on their capability to be integrated with other parts of industrial or military equipment. There are two ways: a growth of the laser design adaptability and a reduction of the external restrictions from other experiments. Requirements caused by COIL integration in real systems may seriously change conceptions of actually important operational characteristics. These changes, in their turn, have to affect to directions of designers’ efforts aimed to both the lasers and the whole systems. Coordination of the efforts from early beginning of the development might allow keeping off many troubles on this hard way.

In this paper we discuss several sensitive diagnostics that have specifically developed for application to COIL and other iodine laser concepts such as AGIL and DOIL. We briefly cover the history of some important diagnostics including recently-developed diode laser sensors for a variety of parameters including: water vapor concentration, singlet oxygen yield, small signal gain, and translational temperature. We also discuss new developments and extensions of prior capabilities including: an ultra-sensitive diagnostic for I₂ dissociation, a new monitor for singlet oxygen yield, and a novel diode laser-based imaging system for simultaneous, multipoint spatial distributions of species concentration and temperature. Finally, we mention how these diagnostics have bee successfully applied to the emerging DOIL technology.

Flow pattern is considered inside the counter-flow jet SOG reaction volume. Similarity criterion for gas flow is found. Two different flow modes appear. Influence of flow mode on output parameters of the SOG is illustrated.

This report describes the experimental and theoretical analysis of a cross-flow jet-type singlet oxygen generator (cross-flow J-SOG) in order to identify the optimal conditions needed to satisfy the ejector-COIL requirement. The optimal conditions had been analyzed under various generator geometries (reaction region length, jet diameter, and chlorine inlet height), gas/BHP flow rates, and gas pressures. The performance was achieved Cl2 utilization of 90% and O₂(¹Δ) yield of 70% at the plenum pressure of 20 Torr.

Experiments with a small scale jet-type singlet oxygen generator (SOG) for a chemical oxygen iodine laser (COIL) were performed in order to find a suitable parameter for scaling to generators with higher chlorine flow rtes. The results of various parameter variations (e.g. overall gas-flow rate, type of diluent gas, length of reactive zone) are shown. Additionally, different types of BHP-injection systems were tested trying to find the best performance of the SOG. The first jet plate is made of Lucite with 49 holes of 0.8mm diameter. Two rows of holes in front of the generator exit are fitted with small injection needles to prevent liquid spill-over. A similar jet plate was designed but with all 49 holes fitted with needles. In another experiment, the diameter of the BHP-jets was varied maintaining a constant total cross-sectional area. A new “sprinkler-type” BHP-injection system is presented, too. On the basis of the previous results a 10kW jet generator was designed and adapted to the 10kW DLR generator test stand. The generator was optimized regarding liquid spill-over. Stable generator operation without liquid spill-over could be demonstrated. The utilization reached values over 90%.

°The cross-flow SOG with filament-guided jets (FJSOG) was developed for COIL. It was found that chlorine utilization strongly depended on chlorine molar flow rate and BHP volumetric rate, and slowly depended on the working pressure for fixed chlorine molar flow rate. The increase of BHP temperature from -25°C to -7C resulted in the increase of chlorine utilization and water vapor fraction in the gas flow from FJSOG. The supersonic COIL with ejector nozzle bank was supplied by oxygen flow from FJSOG. The FJSOG worked very stable without droplet carry out and in laser experiments the clogging of nozzles by dry deposit was not observed. The chemical efficiency more than 24% have been obtained in ejector COIL driven by FJSOG.

A mist singlet oxygen generator is possible to improve the HO₂ utilization at the one pass reaction between basic hydrogen peroxide (BHP) and chlorine. In this investigation, BHP was atomized to small droplets by the gas flow. Chlorine, which is required for stoichiometric reaction with HO₂ in the BHP, was used for atomization of BHP in order to reduce the buffer flow rate for atomization. We obtained the results that the conversion efficiency from chlorine to singlet oxygen (Ux Y) was 9.7% with purely chlorine atomization and 16% with x0.93 dilution ratio of nitrogen buffer at 18.7 mmol/s input chlorine flow and 5.8 ml/s BHP flow rate in a free space reaction chamber.

A 3.6M basic hydrogen peroxide solution is electrochemically regenerated. The apparatus was originally developed for electrolytic H₂O₂ production, generating dilute (<0.2M) BHP for paper manufacturing. To suppress decomposition by various mechanisms, they are identified and quantified. Both caffeine and peracetic acid are found effective to suppress autodecomposition. Theoretical prediction of the current efficiency is made to find an optimum operational condition. A BHP of 3.614M is regenerated to 3.657M with a current efficiency of 67%.

Absorption spectra of chemically produced singlet oxygen O₂(α¹Δ_g) in the vicinity of 1.91 μm wavelength were recorded by intracavity laser spectroscopy technique. The line strengths for Q-branch transitions of the (0,0) band of the b¹Σ_g-α¹Δ_g system were measured. Measurements of the O₂(α¹Δ_g) yield for an electric discharge are presented.

The improvement of the efficiency of singlet oxygen generators (SOG) in chemical oxygen iodine lasers (COIL) is still a key component for optimizing the performance of these lasers. Important parameters for the SOG operation are the utilization of chlorine and the singlet oxygen yield. In this work, the singlet oxygen yield is examined by two different methods: the absorption spectroscopy of ground state molecular oxygen O₂(³Σ) based on a commercial diode laser system in conjunction with a multi-pass Herriott cell, and the measurement of spontaneous emission of the O₂(³Σ)-O₂(¹Δ) transition in the near infrared (1.27 μm). A separate calibration cell has been build with geometry identical to the diagnostic duct of the DLR COIL for exact calibration of the absorption measurement. Results of simultaneously applied emission and absorption measurements are compared. This procedure allows the determination of the radiative lifetime of O₂(¹Δ) to a value of 3730 s.

The analysis of a luminescence spectra of oxygen molecules on O₂(b¹Σ_g,υ’)→O₂(X³Σ_g^-υ") transitions has shown, that vibrationally excited O₂(b¹Σ_g⁺) molecules up to υ=5 are generated in the active medium of chemical oxygen-iodine laser (COIL). Comparison of experimental and calculated results has shown that 4.5 vibrational quanta of oxygen are formed in the active medium of COIL under the deactivation of one singlet oxygen molecule. Dependencies of the threshold of O₂(α¹Δ_g) yield and gain on relative population of vibrationally excited oxygen are studied. The threshold of O₂(α¹Δ_g) yield increases with rising of the relative population of vibrationally excited oxygen and can be some percents more than it was considered before. The gain coefficient weakly depends on the relative population of vibrationally excited oxygen.

We report on recent studies aimed at improving the chemical efficiency of the supersonic chemical oxygen-iodine laser (COIL). Efficiencies around 30% for the supersonic COIL have been the state-of-the-art in the last decade. By carefully studying and optimizing the operation of the chemical generator, the mixing of reagents in different nozzles and the optical extraction efficiency, we achieved a new record (40%) for the chemical efficiency of the supersonic COIL and approached the theoretical limit for this efficiency. The effects of the partial pressure of O₂ and the residence time of the flow in the generator, as well as the heating of the nozzle, are discussed and shown to be crucial in attaining this high efficiency.

The paper reports on the experimental investigations into supersonic oxygen-iodine laser (COIL). Study efficiency results of the COIL unit driven by the singlet oxygen generator (SOG) with twisted gas flow (TA-SOG) are given for supersonic iodine- oxygen mixing at a broadly ranged singlet oxygen pressure and buffer gas flowrate. The measurements were performed for variations of the throat sizes and the positions of the iodine injection plane in supersonic nozzle part. The gas pressure at the input of the nozzle unit was varied from 50 to 150 Torr. The chemical efficiency achieved under optimal operational COIL conditions was 33%.

Supersonic chemical oxygen-iodine laser (COIL) with an advanced mixing nozzle is studied. The mixing nozzle consists of a staggered arrangement of thin wedges lying across the flow duct. Its unique shape looks the letter “X” when it is viewed from the side. To use the new arrangement of iodine injector and the X-wing nozzle, 599W of output power with a chemical efficiency of 32.9% was achieved. This is the highest chemical efficiency of any supersonic COIL reported to date.

A new nozzle bank for an ejector-chemical oxygen-iodine laser consisting of two-dimensional slit nozzles with a trip-jet mixing system was designed, fabricated, and tested in the cold flow operation regime. A computational fluid dynamics (CFD) is used to optimize the trip system design. Horizontal Pitot scan experiments demonstrated that the mixing ability of the trips is excellent. The Mach number of the mixed flow was approximately 3. The average Pitot pressure at the laser cavity was more than 100 Torr. Backpressure tests were conducted, and the results of these tests revealed that the static pressure in the cavity remained constant at approximately 10 Torr until the supersonic diffuser breaks back and the cavity unstarts at a backpressure of approximately 80 Torr.

Theoretical models for chemical lasers depend on a variety of assumptions and empirical data to provide closure and simplify solution of the governing equations. Among the various assumptions and empirical data that have been built into models for chemical lasers are assumptions regarding flow steadiness in the time domain and geometric similarity of the spatial domain. The work discussed here is directed toward elucidating and increasing the understanding of these assumptions commonly used in chemical laser simulation and the impact of their usage upon the predictions of these models. These efforts in turn are directly linked to efforts to achieve improved chemical laser efficiencies and performances as excursions outside the assumed to be 'well understood' traditional operational parameter space are increasingly necessary.

Results of numerical and physical experiments on achieving high efficiency for high power COIL a presented. Different schemes of singlet oxygen and molecular iodine mixing were analyzed. Analyses were made by means three dimensional simulation of processes in COIL nozzle. Model of COIL active medium based on numerical solution of three dimensional non stationary Navier-Stokes equations is developed. For description of gas-cycle chemical processes the scheme consisting of 34 reactions and 12 components of gaseous mixture was used. On the basis of results of numerical simulation of processes in active medium practical recommendations on updating of high-power COIL nozzle bank were made. Practical implementation of proposed recommendations on experimental setup allowed to increase the small signal gain in 1,6 times, achieve chemical efficiency of 31,5% under output power of 14 kW.

The characteristics of mixing between two flows of oxygen and iodine, having different Mach numbers, are numerically examined with the intention of improving the pressure recovery of the exhaust gas of supersonic-flow COIL. Supersonic, parallel mixing system with ramp nozzle array is adopted. The nozzle array has unevenly-piled shape, which is expected to generate vortices and enhance mixing. Three-dimensional, compressible Navier-Stokes equations are solved by means of full-implicit finite difference method. The flow fields are calculated for three types of nozzles, namely, ramp nozzle, symmetric ramp nozzle, and symmetric swept-ramp nozzle. The results indicate that the symmetric swept-ramp nozzle has the best performance.

A negative branch hybrid resonator was coupled to the 10kW-class Chemical Oxygen-Iodine Laser (COIL) device of DLR. Resonator set-up and alignment turned out to be straight forward. Experimentally measured margins for mirror misalignment were found in close agreement to numerical calculations. The extracted power came up to 70% of the power coupled out of a stable resonator device, while the divergence of the emitted light obtained in unstable direction was lower than 2 times diffraction limited.

A negative branch and a positive branch hybrid resonator, suitable for a laser with large optical cross section and small output coupling are explored numerically. The basis of the theory is the Fresnel-Kirchhoff integral equation, the calculations describe a passive resonator. The fabrication of cylindrical mirrors is difficult and deviations in mirror radius of curvature are possible. While a large concave radius of curvature of the mirror is allowed in the stable direction, a convex curvature is not tolerable. Near the ideal mirror parameters, the resonator in unstable direction is insensitive to mirror curvature variations, if the resonator length is appropriately adapted to the actual mirror curvatures. With respect to mirror tilt, the calculations show that in unstable direction the off-axis negative branch confocal unstable resonator is less sensitive than the off-axis positive branch confocal unstable resonator. In stable direction, the sensitivity to mirror misalignment is larger and dependent on the mirror curvature but independent of the unstable resonator part.

New unstable multi-pass resonator concept is reported. It was adopted for 10-kW-class nitrogen-based COIL with low pressure supersonic active medium. Technology and results of the simulation of complex gas-dynamical and optical processes in such resonator are described.

Main gas-dynamic phenomena of COIL are considered as well as theoretical and experimental results. Four parts of COIL are analyzed: SOG, nozzle, resonator cavity and diffuser. Numerical simulation presented of the outer aerodynamics flowfield around the output window at the airplane.

From the geometric parameter study, an optimal ejector design procedure of pressure recovery system for chemical lasers was acquired. For given primary flow reservoir conditions, an up-scaled ejector was designed and manufactured. In the performance test, secondary mass flow rate of 200g/s air was entrained satisfying the design secondary pressure, 40 ~ 50torr. Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser was conducted. Placement of the diffuser at the secondary inlet further reduced diffuser upstream pressure to 7torr. Lastly, the duplicate of apparatus (air 100 g/s secondary mass flow rate each) was built and connected in parallel to assess proportionality behavior on a system to handle larger mass flow rate. Test and comparison of the parallel unit demonstrated the secondary mass flow rate was proportional to the number of individual units that were brought together maintaining the lasing pressure.

Axi-symmetric annular type ejector has been developed as a pressure recovery system for HF/DF chemical laser. Ejector was tested using air as operating gases and low-pressure entrained flow was obtained. In this paper, we changed motive gas since operating gases for chemical laser system are products of chemical reaction. By selection of motive gas, physical properties of operating gas changes, therefore the performance of ejector is different for each motive gas, i.e., specific heat at constant pressure (C_P) and average molecular weight (MW) on the effectiveness of ejection. The research was carried out by both numerical analysis using commercial CFD code, FLUENT and experiments.

Experimental results of investigation of the ECOIL with supersonic nozzles for driver N₂ are presented. Employment of the supersonic nozzles and extremely high-pressure driver nitrogen gives possibility to minimize the plenum oxygen pressure at high oxygen flux, to reach high gain and chemical efficiency.

The slow down process of supersonic flow in channel of chemical lasers - DF-lasers and COIL - is discussed. Particularity of these processes in case of chemical laser is determined by heat generation existing in the active laser medium. Heat generation is determined by physics of laser and lead to reduction of slow down zone - pseudo-shock zone. So diffuser of chemical lasers must be shorter than traditional diffuser.

The aerodynamic windows (AW) are intended for a high power extraction from the gas laser optical cavity, where the pressure is much lower than environment pressure. The main requirements for the aerodynamic windows are to satisfy a low level of optical disturbances in a laser beam extraction channel and an air leakage absence into the optical cavity. Free vortex AW are most economic from a point of working gas consumption and the greatest pressure differential is realized on them at an exhaust to atmosphere. For ideal gas it is possible to receive as much as large pressure differential, however for real gas a pressure differential more than P≥50 is difficult to achieve. To achieve the pressure ratio 100 in free vortex single-stage AW the method of stabilizing of boundary layer was used. The gas of curtain was decelerated in the diffuser and was exhausted into the atmosphere straightly. The pressure recovery improvement was achieved by using the boundary layer blowing inside the diffuser. Only 10% of total mass flow was used for boundary layer blowing.

The concept of 1D subsonic COIL model with a mixing length was generalized to include the influence of variable magnetic field on the stimulated emission cross-section. Equations describing the chemical kinetics were solved taking into account together with the gas temperature also a simplified mixing model of oxygen and iodine molecules. With an external time variable magnetic field the model is no longer stationary. A transformation into the system moving with the mixture reduces partial differential equations to ordinary equations in time with initial conditions given either by the stationary flow at the moment when the magnetic field is switched on or by the boundary conditions at the injector. Advantage of this procedure is a possibility to consider an arbitrary temporal dependence of the imposed magnetic field and to calculate directly the response of the laser output. The results will be compared with the experimental data measured on the subsonic version of the COIL device in the Institute of Physics, Prague.

Two alternative chemical methods of atomic iodine generation for a chemical oxygen-iodine laser (COIL) were studied. These methods are based on fast reactions of gaseous hydrogen iodide with chemically produced chlorine and fluorine atoms. Both processes were studied first in small-scale reactors. A yield of atomic iodine in the Cl system and nitrogen (non-reactive) atmosphere exceeded 80%, while in the F system it was only up to 27% related to F₂ or 50% related to HI. The process of atomic iodine generation via Cl atoms was employed in operation of the supersonic COIL. A laser power of 430 W at 40 mmol Cl₂/s, and the small signal gain up to 0.4%/cm were attained. The proposed methods promise an increase in laser power, easier control of laser operation, and simpler iodine management in comparison with the conventional source of atomic iodine using I₂. The experimental results obtained so far with this experimental arrangement did not proved yet increasing COIL chemical efficiency because some process quenching a part of singlet oxygen was indicated. Therefore a modified experimental set-up has been designed and prepared for further investigation.

New results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. Atomic fluorine was produced at first step by the reaction of molecular fluorine with nitrogen oxide. At second step atomic fluorine reacted with hydrogen iodide producing atomic iodine. It follows from obtained results that two experimental arrangements may be used in COIL. First, atomic F generated in a separate reactor may be injected into singlet oxygen stream with a subsequent HI injection. Second, atomic I may be produced in a separate reactor and then injected into a singlet oxygen stream. It was found that yield of the atomic iodine in the second arrangement may be higher, but a higher loss of I atoms at I atoms injection is anticipated due to wall recombination. The processes of I atoms and F atoms injection will be investigated in a near future.

An instantaneous generation of atomic iodine by subsonic mixing and reaction of ClO₂, NO and HI in the chemical oxygen-iodine laser was calculated by means of 3-D Navier-Stokes equations coupled to the finite rate chemistry model. The numerical simulation predicts high yield of atomic iodine related to HI. The calculated number density of atomic iodine in the supersonic laser cavity is 0.8-1.2 x 10¹⁵ at the stagnation pressure of 5 kPa.

Recent studies of the iodine dissociation mechanism for COIL systems have prompted new investigations of the energy transfer kinetics of O₂(b¹Σ⁺). Additional motivation for these studies, and for investigation of the quenching of I* by O atoms, is derived from efforts to build non-chemical singlet oxygen generators. Discharge generators produce relatively high concentrations of O₂(b) and O atoms. Dissociations of I₂ by the reagent streams from these generators will follow different kinetic pathways than those that are most important when the flow from a chemical generator is used. To improve our understanding of conventional COIL systems, and gain insights concerning the dissociation kinetics that will be relevant for discharge driven COIL devices we have examined the quenching of O₂(b) and O₂(a) by I₂, and the deactivation of I* by atomic oxygen. The primary findings are: (1) Quenching of O₂(b) by I₂ is fast (5.8x10^-11 cm3 s^-1) with a branching fraction of 0.4 for the channel O₂(b)+I₂→O₂(a)+I₂. (2) The quantum yield for dissociation of I₂ by O₂(b) is relatively high (>0.5) and (3) The upper bound for the rate constant for quenching of I* by O atoms is k<2x10^-12 cm³ s^-1.

Singlet delta oxygen (SDO) production in a pulsed e-beam sustained discharge (EBSD) ignited in molecular oxygen with carbon monoxide stabilizing this discharge is theoretically and experimentally studied. Temporal behavior of SDO concentration and yield in the EBSD afterglow is analyzed. Experimentally measured SDO yield for oxygen mixture O₂:Ar:CO=1:1:0.05 at total gas pressure 30 Torr comes up to 7% at specific input energy (SIE) of ~3.0 kJ/(1 atm(O₂+CO)), whereas its theoretical value riches ~ 17.5%. The efficiency of SDO production is theoretically analyzed as function of the SIE.

A new RF plasma jet generator (DSOG-5) of singlet oxygen has been developed for use in an oxygen-iodine laser. The plasma jet was produced in Al nozzles, which were fed by the radio-frequency (100 MHz) power of up to 200 W. The usual mode of operation was an energy transfer from Ar plasma jet to a neutral O₂ gas stream. The yield of singlet delta oxygen was up to 24%. Iodine molecules were dissociated by 200 MHz RF discharge with the power of 60 W prior to injection into the mixing zone of laser. The pre-dissociation enhancement was up to 22% of iodine spontaneous emission intensity. Both the DSOG-5 and the RF iodine pre-dissociation were tested in laser experiments in a transverse flow Discharge Oxygen-Iodine Laser (DOIL). The effluent of DSOG-5 was cooled by liquid nitrogen to temperatures in the range 120-300 K. There was a temperature dependent loss of singlet delta oxygen on the walls. The singlet delta oxygen yield and the atomic iodine luminescence at the wavelength of 1315 nm were measured. The highest luminescence was achieved at pressures of ~1 Torr with the yield of 10-20%. Laser oscillations have not been achieved.

As the development of the electric discharge iodine laser continues, the role of oxygen atoms downstream of the discharge region was found to be very significant. One of the largest uncertainties is the rate of the quenching of I* by O atoms. We have taken a series of measurements of O₂(¹Δ) emission, I* emission, O-atom titrations, gain/absorption, and O₂(¹Δ) yield to explore the significant positive and negative roles that O atoms play in the kinetics of the system that influence the gain. An estimate of the reaction rate for I* + O is provided. This investigation of the effects of atomic oxygen led to the measurement of positive gain on the 1315 nm transition of atomic iodine where the O₂(a¹Δ) was produced in a flowing electric discharge. Excess atomic oxygen was scavenged by NO₂ to minimize the deleterious effects. The discharge production of O₂(a¹Δ) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was followed by a continuously flowing supersonic cavity, which was employed to lower the flow temperature.

Singlet oxygen (SO) concentration exceeding 20% is obtained in pure oxygen with the help of a glow-discharge singlet oxygen generator (DSOG). SO concentration exceeding 30% is obtained using homogeneous or heterogeneous catalysts at 0.5-1 Torr of pure oxygen. The possibility to develop an electrical discharge singlet oxygen generator for oxygen-iodine lasers, which is an alternative to a SO chemical generator is demonstrated.

Experimental and theoretical studies of singlet oxygen excitation in traveling microwave discharge (TMW) are presented. Singlet oxygen O₂(a¹Δ_g) concentrations and atomic oxygen mole fraction have been measured for different pressures, input powers and distances from mw resonator. It was shown that a steady-state traveling microwave discharge with a coaxial cavity resonator could provide maximal O₂(a¹Δ_g) yield of 22% for 2 Torr of pure oxygen and 27-30% for He : O₂ = 1:1 mixture. Developed two-dimensional (r,z) model for calculations of plasma-chemical kinetics, heat and mass transfer was used for simulation of processes in TMW discharge under study. Effects of gas pressure, gas flow rate and input power are studied and compared with experimental measurements of O₂(a¹Δ_g) concentrations and atomic oxygen mole fractions.

A semi-empirical mathematical model is developed for DC glow discharge in oxygen. The calculation results are compared with available experimental data. The basic parameters are revealed. The regularity for singlet oxygen (SO) content variation is found. The SO maximum concentrations and the approaches to its achievement are estimated.

Singlet oxygen excitation in RF discharge at 13.56 MHz was studied experimentally and theoretically in the pressure range of 2 - 20 Torr. It was shown, that the saturation of O₂(a¹Δ_g) concentrations with input power at high oxygen pressures is due to quenching of O₂(a¹Δ_g) by atomic oxygen in three-body process. Removing of atomic oxygen using HgO coatings on the tube wall allows to remove saturation and to increase in three times the O₂(a¹Δ_g) concentrations at 15 Torr. The record values of singlet oxygen (SO) yield of about 10% are obtained for the first time in gas discharges at high oxygen pressures of 10 - 20 Torr.

NCI₃ is a more stable source of NCI(a) than HN₃. The use of NCI₃ as a source of NCI(a¹Δ) for use in an iodine transfer laser has been modeled. The model suggests that gain can be obtained on the spin orbit transition of the iodine atom at 1.315µm in a purely chemical system. New quenching rates of NCI(a) by H₂ and HCI show these species are not a serious problem in scaling the NCI₃ system to high energy densities. The measurements of NCI(a) in our flow tube system are obscured at early times by CI₂(B-X) radiation from the CI atom induced decomposition of NCI₃. We have measured the contribution of this emission and find that the profile more closely matches the profile predicted by the kinetics code. We have measured the yield of CI atoms produced by a microwave discharge of 5% CI₂ in He and find a dissociation fraction of about 25% in agreement with previous studies by Manke and Setser. The yield was measured by titrating the CI atoms with HI and observing the HCI(v=1) radiation. In studies of the production of NCI₃, we have found that the yield of NCI₃ is independent of the gas side mass transfer conditions. Our current reactor produces an NCI₃ yield of about 20% relative to CI₂. Since the production of higher flows of NCI₃ is important for a laser experiment, we present some ideas for scaling NCI₃ to higher flow rates. The use of NCI₃ as a source of NCI(a¹Δ) for use in an iodine transfer laser has been modeled. The model suggests that gain can be obtained on the spin orbit transition of the iodine atom at 1.315µm in a purely chemical system. The experimental data obtained to this point supports the model predictions.

This work revisits the finite-rate chemistry mechanism for AGIL in light of recent rate measurements for kinetic processes. The effect of temperature dependence of kinetic processes measured only at room temperature conditions is explored by assuming a square-root dependence upon temperature in line with kinetic theory. A sensitivity study is performed to elucidate the relative impact of each chemical kinetic process modeled with respect to the larger set of modeled chemical kinetic processes. And reactant mixing is examined, with documentation of the effects of the reactant mixing predictions upon recent multi-watt power extraction experiments.

The effect of NCl(a¹Δ) self-annihilation on the production of NCl(a¹Δ) and energy extraction of NCl(a¹Δ)-I laser was simulated by means of a simplified continuous flow F-P resonator model. The results show that NCl(a¹Δ) self-quenching is an important influence on NCl(a¹Δ) production and energy extraction of NCl(a¹Δ)-I laser and is the most important channel for transport losses of NCl(a¹Δ). The efficiency of NCl(a¹Δ) production with NCl(a¹Δ) self-annihilation is much less than that without NCl(a¹Δ) self-annihilation. The optimal location for cavity resonator, the profile of power density along the flow direction and the total power are dramatically dependent on the order of magnitude of the rate constant of NCl(a¹Δ) self-quenching reaction. The results show that it is necessary to do more works on the measurement of the rate constant of NCl(a¹Δ) self-annihilation reaction and its dependency on temperature in order to accurately analyze, design and value AGIL(All-gas Phase Iodine Laser).

The paper considers the physical principles of developing the fullerene - oxygen - iodine laser (FOIL) with optical (sunlight in particular) pumping. Kinetic scheme of such a laser is considered. It is shown that the utmost efficiency of FOIL may exceed 40% of the energy, absorbed by fullerenes. Presented are the experimental results of singlet oxygen generation in liquid media (solutions and suspensions) and in solid-state structures, containing either fullerenes or fullerene-like nanopartickles (FNP). In experiment was shown the possibility of the singlet oxygen transfer to the gaseous phase by means of organizing of the solution (suspension) the boiling as well as of the gasodynamic wave of desorption from the solid-state structures, containing fullerenes or FNP. We present the preliminary experimental results of pulsed generation in optically pumped FOIL with the use of primary photodissociation of iodide for preparation of the atomic iodine in the generation zone. In the experiments on FOIL generation was implemented the principle of spectral separation of optical pumping.

The singlet oxygen generator development is the basic problem of fullerene oxygen iodine laser design. Physival principles of singlet oxygen generator on the base of solid-state fullerene-containing structures were investigated. The solid-state singlet oxygen generator is a surface of membranous structures with embedded fullerenes (fullerites) of fullerene-like nanostructures - astralenes. Singlet oxygen is generated by interaction of molecular oxygen, sorbed by the surface and fullerene-like nanostructures, photoexcited by optical pump. The singlet oxygen entrance in gas phase occurs as a desorption wave, caused by surface heating by optical pump. The effectiveness of molecular oxygen sorption by fullerene C₆₀ and astralen depending on temperature, the extent of nanostructures heating, oxygen pressure and morphology of coating was studies.

Chemical oxygen-iodine laser (COIL) has a great potential for applications such as decommissioning and dismantlement (D&D) of nuclear reactor, rock destruction and removal and extraction of a natural resource (Methane hydrate) because of the unique characteristics such as power scalability, high optical beam quality and optical fiber beam. Five-kilowatt Chemical oxygen-iodine laser (COIL) test facility has been developed. The chemical efficiency of 27% has been demonstrated with a moderate beam quality for optical fiber coupling. Our research program contains conventional/ejector-COIL scheme, Jet-SOG/Mist-SOG optimization, fiber delivery and long-term operation.

First results of experimental and theoretical investigations related to an industrial application of oxygen-iodine laser (COIL) are reported. A developed calculative model determines a transmission factor of a laser emission at a set wavelength depending on the waveguide parameters, focusing system characteristics, and laser emission intensity angular distribution. Carried out investigations concerned with delivery of a laser emission power up to 1.6 kW via industrial quartz waveguides of 0.8- and 1 -mm- diameters and 3 and 10 meters long. It was shown that at optimal parameters of the delivery system the waveguide transmission is virtually independent of the diameter and bending radius and is equal to 0.90±0.02, which is in a good agreement with calculative results. The spatial distribution of the laser intensity at the waveguide input and output was measured. The far-field divergence at the 90%-level of the power was shown to increase approximately by 4 times when the laser emission is propagated through a quartz waveguide with a 800-mkm-diameter core and 3 m long.

First results of experimental and theoretical investigations concerning an industrial application of oxygen-iodine laser (COIL) are reported. The dependencies of the largest cut depth on the laser emission power, cut width and rate, and kind of processing gas (oxygen or nitrogen) were determined for carbon and stainless steels, and aluminium alloys. A developed simple engineering model determines parameters of separating gas-laser cutting of metals allowing for principal channels of heat loss: warming, melting, material evaporation and heat conductivity, convection and radiant heat exchange. It was shown that when oxygen is applied as a processing gas it is necessary to take into account the additional heat emanation that is usually about 10% of the material oxidation energy. A good agreement between calculative and experimental data was obtained.

The transmission of chemical oxygen-iodine laser (COIL) emission through several kinds of multimode quartz optical fiber is measured in order to explore the applicability of COILs for the extraction of natural resources. The minimum transmission loss through these fibers is 0.64 dB/km, and high-power transmission for a distance of kilometers is shown to be feasible. Laser emission at an average input power of 1 kW is successfully transmitted through a multimode optical fiber for a distance of 1 km with an efficiency of 80%.

Possibilities to extract methane from methane hydrate are discussed. COIL is a unique solution from technological and economical stand points and systems for excavation are proposed

Simulations of an explosively pumped two-stage photo-dissociation iodine laser with an SBS mirror at laser aperture 15 cm have shown a good agreement of calculation and experimental data on energy, laser power dynamics, brightness and Strehl number of output radiation. Calculations and experiments show that parasitic reflections of laser radiation from the windows of amplifiers and elements of the optical scheme are a reason that the brightness value is frequently less than maximum possible one. It is found that the input intensity should exceed 10-20 W/cm² for eliminating the harmful effect of parasitic reflections on brightness. The brightness increasing is promoted as well by reducing the SBS threshold and displacing the second amplifier towards the SBS mirror at retaining a total length of the system. Under optimal conditions the maximal brightness reaches 10¹² J/sr.

Effect of different excitation parameters on discharge stability in mixtures with SF₆ and efficiency of discharge non-chain HF(DF)-lasers is studied using excitation by inductive and LC-generators. Experimental conditions providing maximal performance of discharge non-chain HF(DF)-lasers are determined. Uniform electric field in the laser gap, uniform preionisation, relatively short current pulse duration and input energy around 50-70 J/l provide perfect discharge uniformity and greatly improve electrical efficiency of the discharge HF(DF)-laser. Intrinsic efficiency of discharge non-chain DF and HF lasers up to η_in=7-10%, respectively, close to that obtained with an e-beam initiation is obtained. Electrical efficiency of the lasers up to η₀=5-6% with the output over 1 J was demonstrated for the first time. The effect of preionisation on volume discharge formation in mixtures of H₂ and hydrocarbons with SF₆ is suggested, processes affecting the laser efficiency are discussed.

A few years ago, it has been demonstrated that the use of hydrocarbons such as C₂H₄ or C₆H₁₂ as hydrogen donor allows realizing high-volume discharges in SF₆ based non-chain HF/DF gas mixture. Although high energy, short pulses and high repetition rates have been obtained, for some uses the specific output energy, the efficiency and, to a less extent, the optical quality of all these lasers remain insufficient. IT appears now that the only way to increase these values is to use chain reaction. But chain reaction is known to be delicate to control, especially when working at high repetition rate. This paper will describe recent work directed towards a better understanding of the discharge mechanisms and an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers using chain reaction in discharge initiated repetitive and non-repetitive experiments. High volume discharge cells compatible with repetition rate have been realized. Discharge initiated repetitive chain reaction ash been studied up to 10Hz with large gap. Efficiencies as high as 70% have been obtained in single pulse experiments. Computer modeling allows now predicting satisfactorily the performances of discharge-initiated chain reaction HF/DF lasers as a function of electric circuit characteristics and gas composition.

An experimental study was carried out of pulse-periodic (rap-rate) operation of a CW chemical HF laser with optomechanical up to 10³ Hz Q-switched cavity. Output pulse power shown increases at the experimental conditions no less than five-fold through the frequency region of 17-250 Hz. Average power of the rap-rate output reduced considerably comparatively to the same of CW mode operation, but shoot up with growing of the modulation frequency (in the same frequency region) faster than peak pulse power. It were discussed the possible causes of experimental and calculation characteristics differences of laser.

The efficient repetitively pulsed (10 Hz) HF chemical laser initiated by barrier electric discharge with electrode gap 10 cm was realised. In mono-pulse mode specific output energy 3 and 23 J/l, technical efficiency (η) 3.4 and 26%, for non-chain and chain process, correspondingly, were obtained. In the repetitively pulsed (RP) mode of the laser operation at 10 Hz on the depleted fluorine-hydrogen mixture (20% F₂, 5% H₂) the mean laser power of 43 W was obtained (specific output energy E/V ~ 10 J/l, η=11.3%). The computational prediction for laser operation in repetitively pulsed mode at active length of about 0.5 m has shown the possibility of achievement of the specific laser energy about 15 J/l and technical efficiency up to 20%. Output laser specific energy ~ 14 J/l under RPCL conditions at length of active medium 0.37 m in mono-pulse mode was obtained in a good agreement with numerical prediction.

The paper presents the results of investigations into formation of a laser beam energy density distribution in the near-field zone of an electric-discharge HF-laser with inductive discharge stabilization. The investigations were performed on HF-laser with an H₂-SF₆ active mixture for the interelectrode gaps of 34 mm and 52 mm. In the experiments were used the electrodes with 60 mm wide, formed by the plates with the thickness of 1 mm and the width of 60 mm or 120 mm, which were located at the angle 30° to the optical axis. The electrodes width of 30 mm was formed by the plates with width of 60 mm, located at the angle 30° to the optical axis. The laser energy density distribution in a laser cavity with plane mirrors and discharge emission intensity distribution over its cross section were studied experimentally. It was found that the laser beam profile in the near-field zone and the profile of discharge emission intensity distribution are close in shape. Locating electrode plates at the angle 30° it is possible to increase significantly a generation zone width. For both interelectrode gaps the full width of a laser energy density distribution at half maximum made up ~ 80% of the electrode width.

The development of a TEA HF (SF₆:C₃H₈:He) oscillator-double amplifier laser system with one common switching element and one common power supply unit is presented. All three cavities employ the conventional charge transfer excitation circuit and the surface corona discharge preionization scheme. For each amplifier the small signal gain coefficient g_o and the saturation energy density E_s are determined and their dependence on the charging voltage and the active gas concentrations is investigated. The performance characteristics of the laser system i.e. maximum output energy, pulse duration, spectral and beam profile evolution through all three stages of the system are given. Additionally, beam propagation measurements through a 150cm long, 250μm core diameter GeO₂ mid-IR fiber are presented.

The feature for DF laser ecology applications in its ramified spectrum. The DF laser energy distribution in selective and non-selective modes is investigated. The non-selective and selective outputs were 42.7 and 128 (totally) mJ accordingly.

An overview of how high energy laser system illuminator requirements are developed, along with a short history and current status of diode-pumped solid-state laser illuminator technology development in the United States, will be provided.

In our diamond-cooled approach, thin disks of laser gain material, e.g., Nd:YAG, are alternated between thin disks of single crystal synthetic diamond whose heat conductivity is over 2000 W/m-°K. The gain medium is face-pumped (along the optical axis) by the output of laser diode arrays. This optical configuration produces heat transfer from Nd:YAG to the diamond, in the direction of the optical axis, and then heat is rapidly conducted radially outward through the diamond to the cooling fluid circulating at the circumference of the diamond/YAG assembly. This geometry effectively removes the heat from the gain material in a manner that permits the attainment of high power output with excellent beam quality.

60 mJ chirped-pulse power was obtained using a diode-pumped regenerative amplifier with a cooled Yb:YLF crystal at 20 Hz repetition rate. After temporal compression, 36 mJ, 795 fs pulses were generated. Our numerical calculation shows that 100 mJ output power at 1 kHz would be obtained by using a sapphire-sandwiched laser material and a 2-pass amplification scheme in regenerative cavity.

Quantum-defect-limited operation in a diode-pumped Yb:YAG oscillator have been demonstrated at low temperature. The highest slope efficiency of 90% was obtained with M²=20 at the crystal temperature below 70 K, which was close to the theoretical stokes efficiency of 91.2% (λ_pump/λ_laser=941nm/1030nm). An optical-to-optical efficiency and a laser gain were 74% and 8 cm^-1, respectively, at a low pump intensity of 1.3 kW/cm². After optimizing a spatial mode coupling between a diode pump laser and a TEM00 cavity mode on the crystal, 80% slope efficiency and 70% optical efficiency were still high at M²=1~1.5.

The saturable absorbers (Cr⁴⁺:YAG, GaAs and LiF crystals for 1064-nm wavelength, V³⁺:YAG crystals for 1340-nm respectively) were examined as passive Mode Lockers and Q-switches in diode pumped Nd:YVO₄ lasers in the Z-type resonators. In each case, partially modulated long trains of QML pulses were observed. As a rule, envelopes with about 1 μs duration and more than 50% depth of modulation were observed. For stabilization of the mode locking trains nonlinear crystals (KTP or LBO) as negative feedback elements were inserted. The fully modulated QML trains for intracavity II harmonic conversion at 670-nm wavelength in V³⁺:YAG Q-switched Nd:YVO₄ laser with LBO crystal were demonstrated.

Preliminary tests are here reported, carried out on a compact and rugged diode pumped solid state (DPSS) laser for industrial applications. The laser design is based on a Neodimium doped slab shaped ceramic YAG medium. A maximum extraction of more than 320 W at a 44% slope efficiency level has been obtained with a simple half symmetric stable resonator scheme. Experimental data together with F.E.M. simulations indicate that power extraction can be scaled up to a multi-kilo Watt level with this extremely compact (overall dimensions: 160 x 100 x 60 mm) laser head geometry. A narrow transverse direction Beam Parameter Product (BPP) of the order of 3 mm.mrad is experimentally obtained. This enables the reasonable prediction of a good quality beam extraction adopting a stable multipass resonator or a hybrid stable-unstable resonator. Given the zig-zag resonator path, thermal lens effects appear scarcely critical.

Flashlamp pumped oscillator - three amplifiers Nd:YAG picosecond laser system mode-locked with multiple quantum well (MQW) saturable absorber was developed and investigated. 80 ps long pulses with the energy of 120 mJ were generated.

A specially developed monolith crystal, which combines in one piece cooling undoped part (undoped YAG crystal), active laser part (YAG crystal doped with Nd³⁺ ions) and saturable absorber (YAG crystal doped with V³⁺ ions), was used for construction of longitudinally diode pumped Q-switched Nd:YAG laser operating at wavelength 1342 nm. The monolith consists of 4 mm long undoped part bounded to the V:YAG saturable absorber 530 μm thick which gives the initial transmission of saturable absorber 88%. The diameter of whole monolith was 5 mm. This combination of active crystal and saturable absorber allows to realize more compact resonator with the shortest cavity length of 33 mm only. The monolith was mounted in an adjustable water-cooled cupreous ring. Temperature of cooling water was in a range from 12 to 14 °C. As a pumping source the CW-operating laser diode emitting radiation at wavelength 808 nm with the maximum output power 20 W at the end of the fiber (fiber core diameter 400 &mu;m, numerical aperture 0.22) was used. The diode radiation was focused into the active Nd:YAG crystal by two achromatic doublet lenses with the focal length of 75 mm. The measured diameter of pumping beam focus inside the crystal was 360 μm. The resonator of the Nd:YAG laser was formed by a planar dielectric mirror with high transmission for the pumping radiation (T>98%@808nm) together with the high reflectance for the generated radiation (R=100%@1340nm), and by a concave (100mm or 146 mm) dielectric mirror serving as an output coupler. As this coupler a various dielectric reflectors (with the reflectivity from 82% up to 94%) was used with the reason to obtain the shortest giant pulse with the maximum power. As the optimal, the stable CW Q-switched output at wavelength 1342 nm with length of pulses 11 ns with repetition rate 6.4kHz and peak power 6.1kW, was obtained.

For many applications (in medicine and industry) powerful mid-infrared radiation can be useful. For this reason, Q-switch operated Er:YAG laser and corresponding delivery systems are necessary. We report about specially designed LiNbO₃ Pockels cell by help of which the short 60 ns mid-infrared pulses were generated. For giant pulse generation two Brewster angle cut LiNbO₃ crystal was inserted inside the oscillator and a specially designed driver ensured the precise time of Pockels cell switching. The optimization of the input parameters (high voltage value and Pockels cell switching time), which can have an impact on the output pulse characteristics, was performed. For the optimal found delay value 450 μs and the applied high voltage 1.4kV on the Pockels cell, giant pulses with length of 60 ns and energy of 60mJ were generated. It gave 1 MW of the output peak power. These powerful infrared pulses (λ= 2.94 μm) were delivered by the help of specially designed cyclic olefin polymer-coated silver hollow glass waveguide with the inner diameter 700 μm and length of 1 m. For the contact treatment sealed cap was used. The measured transmission of the whole delivery system was 76.5% which gave the output interaction intensity 79 MW/cm².

We present in this paper the highest, to our knowledge, average output power and conversion efficiency at 1572-nm signal wavelength for intracavity optical parametric oscillator (IOPO) inside acousto-optic Q-switched Nd:YVO₄ laser end pumped by 15-W power fiber coupled diode. The Nd:YVO₄ laser of the 147-mm long cavity gives 3-W average output power at 1064-nm wavelength at repetition rate 40 kHz. The additional separating mirror and x-cut KTP crystal form, with the output coupler high reflective at 1064-nm and partially transparent at 1572-nm wavelength flat-flat IOPO resonator of 35-mm length. We have achieved 3-ns duration pulses for 20-mm long KTP and 4-ns duration pulses for 30-mm KTP length, respectively. Up to 1.5 W of an average power at the signal wavelength for 40 kHz repetition rate of acousto-optic Q-switch was demonstrated. Due to intracavity gain guiding effect, diffraction limited signal beam was achieved. Maximum peak power of 10 kW was demonstrated. Conversion efficiency of 50% with respect to Q-switched output at 1064-nm wavelength and 11% with respect to diode pump power were achieved.

We describe methods for time-multiplexing of high power diode lasers. This means that high power laser pulses emitted from a set of laser diodes are guided on a common optical path via an optical multiplexer with the aim to build a high beam quality diode laser. We examined pulsed operation of laser diodes and developed elements for a digital multiplexer suited for this special task. The technology developed until now will allow a device multiplexing 4 laser diodes with a power of 16W and a beam quality of one laser diode. Time-multiplexing of 8 laser diodes for a device with 30W should be feasible as well.

Experimental results based on rare-earth-doped fibers have impressively shown that fiber lasers and amplifiers are an attractive and power scalable solid-state laser concept. Based on ytterbium-doped large-mode-area (LMA) double-clad fibers in the continuous regime output powers approaching the kW-range with diffraction limited beam quality have been shown. Average output powers in the order of 100 W even for nanosecond fiber amplifiers have been demonstrated in the pulsed regime. Further power scaling is limited by nonlinear effects, thermo -optical problems or amplified spontaneous emission. In our contribution we discuss power scaling of fiber lasers and amplifiers in the multi kW-range with excellent beam quality based on rare-earth-doped fibers.

A new type of multi-clad rare-earth doped silica fiber was designed, prepared and tested for the power scaling of high power fiber lasers in the 1 .1 tm wavelength region. By means of a dedicated laboratory setup a maximum output power of more than 1 .300 watts with excellent spectral and beam behavior was achieved. The fundamental investigation of the energy transfer processes and of the fluorescence lifetimes of different Nd:Yb co-doped has been studied. Such fiber-lasers were tested in the laboratory at several materials (plastics, metals, glass) in the fields of material processing and micro-marking, respectively.

Last years, CO laser physics has been advanced by researches of CO overtone laser operated on high vibrational levels. An extension of kinetic model to multi-quantum vibration-vibration exchange and development of fully self-consistent model of CO laser are described. The theoretical model developed is verified by comparison with experimental data on overtone CO laser characteristics and laser gain dynamics. Current status of experimental achievements in CO laser characteristics in both fundamental and overtone bands are reported.

Time behavior of gas temperature in CO containing gas mixture excited in pulsed electron-beam sustained discharge (EBSD) was experimentally studied under different experimental conditions. To study time behavior of gas temperature, the fact that the gas temperature is equivalent to the rotational temperature of gas molecules was used. Rotational distribution of the excited states of CO molecule was reconstructed from measured small-signal gain dynamics on different ro-vibrational transitions. The time behavior of small-signal gain was obtained with probe low-pressure CW CO laser for ten ro-vibrational spectral lines. Gas mixtures CO:He=1 :4 and CO:N₂=1:9 typical for a CO laser were used. It was demonstrated that gas temperature grew from 1 10 K (initial temperature) up ~15O K for the first hundred microsecond after EBSD beginning and was staying at this value for a long time (more than 1 ms) for both gas mixtures. EBSD pulse duration was -3Oµs. The method of reconstruction of gas temperature time history was also applied for oxygen gas mixture CO:O₂=1:20 at gas pressure 0.04 atm, which was used for obtaining singlet delta oxygen in EBSD. The method can be used for diagnostic of non-equilibrium gas mixtures containing CO molecule.

Small-signal gain time behavior for cryogenic pulsed e-beam sustained discharge CO laser amplifier on high (V>15) fundamental band vibrational transitions was studied experimentally for different CO containing gas mixtures including ones typical for CO lasers and amplifiers (CO:He and CO:N₂), and CO:O₂ used for singlet delta oxygen production.

An automatic output-stabilized CO-laser model tunable within a broad spectral range (-300 cm^-1) and based on a sealed-off active element with life time approximately 3,000 hours has been created. Such laser find ever expanding applications to solving numerous problem sets in ecology monitoring, medicine, spectroscopy, metrology, nonlinear optics, communication systems, laser chemistry, diagnostics of active media of high-power CO lasers and other areas.

A high average power TEA CO₂ laser employing rotating spark gap switch is described. Average power up to 12kW has been achieved at the repetition rate of 400Hz.

By coupling a CW C0₂ and a TEA CO₂ laser through a grating simultaneously used for both resonators, without any additional optical elements, the CW laser radiation was injected without loss into the TEA CO₂ laser optical cavity. Thus, longitudinal and transverse single mode operation of the TEA CO₂ laser was achieved successfully without any intracavity limiting apertures an evident by the smooth shape of detected pulses. Furthermore, a 3x3 cm cross section single mode beam with unaffected energy of about 4 J/pulse was obtained. This specially designed array due to its observed spectral coincidence of CW radiation and pulsed emission indicates exact alignment of injected CW radiation with the optical axis of TEA CO₂ laser resonator without significant angular deviation. Slight radial deviation, however, did not have any detectable destructive effect on the single mode output signals. This compact and simple structure single mode TEA CO₂ laser with its stability and simple adjustability can be very useful particularly for portable units such as atmospheric lidar instruments.

Image drawing using a laser system has been attempted by Segmented Pixel Drawing (SPD) method and Laser Plastic Coloring (LPC) method in our laboratory. Laser dot processing by a short pulse oscillation of a CO₂ laser is used for these laser methods. Stable short pulse oscillation is required for an accurate image drawing. That oscillation has a tendency to be unstable because of its long oscillation interval. A tickle pulse is known as one of a technique which is conventionally used for a continuous pulse oscillation of a CO₂ laser in order to make rising rate of laser oscillation quick. In this study, this tickle pulse has been improved and applied to the short pulse oscillation in order to stable short pulse oscillation and high accurate laser dot processing. In the result, processed dots are appeared bigger with less variation in their sizes with the improved tickle pulse case compared with the conventional case. Short pulse oscillation is stabilized by these improved tickle pulse. Reproducibility and accuracy of the SPD method and LPC method might be realized by this stabilized dot processing.

The studies on a 1 00-Joule-class UV-preionized TEA (transversely excited atmospheric) CO₂ laser are reported. A maximum pulse energy 1 15 J was obtained by using an energy-optimized gas mixture of C0₂/N₂/H₂ =3/15/2 and a Marx pulse generator discharge circuit. The temporal waveform of the laser pulse with the optimized gas mixture consists of a sharp spike of 250 ns and a tail of 4 µs in full width at half maximum (FWHM). Simple air breathing laser propulsion was demonstrated, a high impulse coupling coefficient 390 N/MW was obtained at the pulse energy 60 J, which shows the attractive point ofthe UV-preionized TEA CO₂ laser.

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We studied the characteristics of supersonic CO₂ laser excited by RF discharge in closed-cycle. The relation between output power and Mach number is disclosed in this paper.

Radio frequency capacitive discharges (RFCD) in the frequency range 1-200 MHz are widely used for gas lasers pumping. Magnetic field has an efficient effect on many plasma processes. When we apply a uniform magnetic field to a rf excited plasma, the electron mobility in direction perpendicular to the magnetic field is reduced. The reduction in the electron mobility leads to a decrease in drift velocity of electrons. In rf excited gas discharges thickness of sheaths is equal to amplitude of electron drift oscillations. So the reduction in the drift velocity of electrons leads to reduction in thickness of sheaths. As we know, small signal gain of active medium in rf excited CO₂ lasers in bulk plasma region is much more than that in sheaths. Thus it can be concluded that applying magnetic field to rf excited CO₂ lasers leads to an enhancement in thickness of positive column and output power. Experimental results show an external magnetic field leads to an increase in output power of rf excited CO₂ lasers. Furthermore, in this paper we use a one dimensional model to show external magnetic field effects on some discharge parameters such as V-I characteristics, intensity of emitted light from plasma, impedance of sheaths and positive column of plasma for mixture of 10% CU₂, 10% N₂ and 80% He at pressure of 100 mbar theoretically.

Output characteristics of a planar RF-excited waveguide CO₂ laser with 150W output power is investigated, including the divergences in stable and unstable directions, and influences of mirror misalignment and resonator length variations on the output power and mode structure of the radiation.

The paper presents a new approach for radiation mode formation, based on the proper choice of the discharge electrode's shape and the distance from the resonator's mirrors to the butt-end of electrodes. In theory and in experiment was shown the possibility to select the basic waveguide mode of radiation. For 2.5 KW slab CO₂ laser, excited at 40,68MHz, was obtained the near diffraction-limited divergence.

The isobaric fluctuations of temperature and density, attending with turbulent adiabatic fluctuations of velocity, have been evaluated under spatial non-uniformity of temperature and at heat generation in the incompressible flow. The character of their quantity dependence on spatial scale has been revealed. It has been shown that the temperature gradient and specific power of heat generation strongly affect the isobaric fluctuations of temperature.

Thermodynamic and optical parameters of the CO₂ slab-waveguide pulsed laser are given. The methodology of the investigations is based on a known Gladstone-Dale formula, linking the refractive index of the fluid, density (or pressure), and temperature of the medium.

Theoretical and experimental study of transverse optical pumping of the high-pressure multi-component (CO₂+N₂O)-laser medium is carried out. Possibility of high efficiency (15 - 20%) of conversion of the discharge pulsed HF-laser radiation (λ = 2.7 - 3 µm) with the pulse duration <1 µs to the stimulated emission (10 - 11 µm) of the broadband laser medium is shown.

A model is developed for the breakdown and regeneration of component gases in an industrialised TEA CO₂ laser, both with and without internal catalysts, and is found to be in excellent agreement with experimental data. The laser was found to be stable at O₂ levels in excess of 2%, whereas previously reported values suggest stable operation at values of less than 1%. This is thought to be related to the unusually high starting CO₂ concentration of the gas mix, and the short time pulse of the laser ouput. Long term catalytic behaviour however shows a decay in the catalyst activity, corresponding to higher energy variation and lower average power.

The IGBT (Insulated Gate Bipolar Transistor) is a modern solid-state switch with wide spread applications in power electronics. However, little information is available on the performance and reliability of the switch in pulsed power supplies used for the excitation of CO₂ TEA and excimer lasers. Results of reliability test conducted on a high-power, high-voltage IGBT are presented with additional focus on the measurement technique. It is found that IGBTs can be reliably used in pulsed power supplies where the peak switching current exceeds the average current rating up to five times. Furthermore, IGBTs can be reliably connected in series to increase the switch operating voltage.

The performance of 100W small-scale "second-generation" kinetically-enhanced copper vapour lasers of active length im long and volume O.25-O.8L are reviewed. These systems have substantially reduced plasma tube insulation so that the lasers operate in a regime of high heat flux. The specific output powers are a factor of 2 higher than "first-generation" kinetically-enhanced copper vapour lasers and five-fold higher than copper vapour lasers operating without HCl additive. It is shown that the spatio-temporal gain characteristics remain well suited to efficient extraction of high beam quality output, as an amplifier or oscillator using unstable resonators. Radially-resolved measurements of the Cu density indicate that the plasma properties are much closer to equilibrium than expected from thermal models, indicating promise for further increases in specific output power. The implications for specific output power of H₂:CuBr and Cu HyBrID lasers are also considered.

Investigations of the output parameters of CuBr (Cu)+HBr laser systems have shown that HBr additives to the CuBr laser active medium result in an increase ofthe laser output power and efficiency that compares, in this case, with that of a CuBr laser with H₂ additives. It has been found that the vapor of working substance are additionally produced in gas-discharge tubes (GDTs) less than 2 cm in diameter due to expulsion of copper atoms from the GDT walls by HBr. The results of simulating the kinetics of the copper vapor laser active medium with HBr additives show that the enhancement of the laser performance parameters can be explained by the processes of chemical transformation of copper from the solid phase into the gas one.

A large volume laser tube of dimensions 80-mm inner diameter by 3-m long (15.1 litres) has been built for the study of extrapolation in power of the Cu-Ne-HCl-H₂ laser medium. A high power (77 kW) all solid state high voltage power supply has been also used for this purpose. Results show an improvement of the optical power after the HCl/H₂ mixture injection. An optical power of 312 W has been extracted from this laser head in oscillator configuration.

A laser tube construction for the UV Cu⁺ Ne-CuBr laser with a resource exceeding 500 hours is developed and investigated. The laser is operated at a periodic refreshment of the buffer gas mixture - 16.7 Torr Ne and 0.03 Torr H₂. In this regime for a 500-hour laser action the average output power is maintained about 600mW.

High efficiency optical pumping of 4-μm HBr-laser was performed by the principal 2P9 line (3.836 μm) of pulsed DF-laser. Precise coincidence revealed of this laser transition with R2 line of the fundamental absorption band of the heavy isotopomer of hydrogen bromide was utilized. Lasing within 0.3-15 Torr pressure range was observed in overall (4.017-4.215) μm spectral range, at both off-axis and the collinear pumping geometry (pump fluence of 0.2 - 0.4 J/cm², pulse FWHM duration ~300 ns). Complex behaviour of HBr-laser emission peak intensity, pulse duration and time delay upon the gas pressure was analyzed. Energy conversion efficiency at P=10 Torr was increased from ~2% to more than 5%, when collinear scheme with better mode-matching was utlized. It is believed that the efficiency may be additionally improved by optimization of HBr-laser cavity losses.

It has been shown that a volume discharge is forming in a non-uniform electric field at a short voltage pulse rise and pulse nanosecond duration without preionization in different gases under pressures above atmospheric (helium 6 atm, nitrogen 3 atm).

A number of laser transitions in the region of 12-13 μm have been obtained by optical pumping of NH₃ molecule using a tunable TEA CO₂ laser. By studying several different experimental arrangements, it is shown that the optimum pure NH₃ gas pressure at room temperature is about 5 mbar. Moreover, some buffer gasses such as N₂, H₂ and He were employed and it was found that He is the most efficient gas for which the maximum efficiency up to 8% with the mixture of NH₃: He =7:16 was obtained. In this condition, the maximum energy per pulse of 125 mJ was achieved. The tunable operation of this laser was established in two distinct wavelengths of 12.812 μm and 12.08 μm.

The genesis of excimer lasers is reviewed. Contrary to previous retrospectives, the present analysis is restricted only to physics and technics of discharge pumped Rare-Gas Halides (RGH) excimer lasers. Some side factors like politics or human personality, interfering the development of excimer technology, are also discussed.

The experiments have been performed at 100-J-class GARPUN KrF laser installation, which consists of 20-ns discharge-pumped master oscillator and two stages of e-beam-pumped amplifiers with gain volumes of 10x10x100 cm and 16x18x100 cm. Gain and absorption coefficients were measured in a single-pass scheme, while intrinsic efficiency of about 12% was demonstrated in the saturated double-pass amplification. They were compared with numerical simulations. A numerical code solved a set os simultaneous self-consistent kinetic equations together with amplification of laser radiation and spontaneous emission in large-aperture KrF lasers. Being verfied with the experimental data the code was used to forecast the parameters of IFE-scale KrF amplifiers.

High-pressure gas discharge experiments are carried out in a novel three-electrode prepulse-mainpulse configuration with two discharge volumes. The design is capable to break down both x-ray preionized volumes at the same time. First experiments in Xe/HCl/Ne mixtures reveal spatially very homogeneous discharges for up to 350 ns with a power deposition of 260 kW/cm³. For discharges in Kr/HCl/Ne mixtures we observe also very homogeneous discharges for a similar long pulse duration when a low krypton concentration of 10 mbar is used. For discharges in mixtures with a higher krypton concentration of 100 mbar we still observe very homogeneous discharges for 200 ns. Furthermore the total discharge current is established 8-10 times faster than in other systems.

Results of experimental and theoretical investigations of pump discharge and generation of XeCl laser with 0.21 J laser energy, 2.7% electric efficiency nad 20 ns (FWHM) pulse duration are presented. The influence of step ionization, dissociative attachment and recombination processes on an active volume spatial uniformity and radiation parameters is shown.

Compact excimer laser systems were developed for industrial applications especially for micro-machining applications. Therefore all components and modules are designed for long-term operation and long maintenance intervals. By using new designs and technologies the performance of these laser systems could be improved in comparison to the well-known compact excimer lasers. The result of the first tests of the prototype are presented. The laser tube lifetime could be more than doubled in comparison to the former laser design. Additionally maximum repetition rates of 2kHz were demonstrated for the prototype 193 nm laser systems. A maximum pulse energy of about 40 mJ was measured. The pulse-to-pulse stability was reduced below 1% (one sigma) in the working area of the laser. The state-of-the-art of compact excimer lasers will be presented and outlook for the future will be given.

A 250 J/210 ns four-stage XeCl laser system named Photons has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.

Output radiation performances of XeCl laser with 10x10x80 cm³ active medium dimensions depending on pumping circuit parameters, intensity and uniformity of preionization have been researched. It was shown that radiation pulse duration and accordingly discharge uniformity depend first of all from preionization homogeneity and not from its intensity.

The Ar₂* excimer production kinetics were initiated by electrons produced in the optical-field-induced ionization (OFI) process. The use of an Ar-filled hollow fiber extended an OFI plasma length up to 30 cm. By use of a 126-nm mirror, the maximum one-pass gain coefficient at 126 nm was observed to be 0.58% cm^-1 at 10 atm Ar.

The generation of KrCl*, and Cl₂* excimer radiation by the sliding discharge has been investigated. The partial pressures of components of working mixtures and excitation conditions were optimised. The UV radiation power density of 55 mW/cm² was obtained. The efficiency of the source with respect to input average power was ≤10%.

An electric-discharge XeF-laser with a pulse repetition rate up to 4 kHz was developed. The laser electrode unit was made on the basis of plate-like electrodes with inductive-capacity discharge stabilization. The narrow discharge width ≤ 1 mm was realized. The buffer gases He and Ne with NF