Laser and discharge parameters in mixtures of rare gases with halogens driven by a pre-pulse-sustainer circuit technique are studied experimentally and theoretically. Inductive energy storage with semiconductor opening switch was used for the high-voltage pre-pulse formation. It was shown that the pre-pulse with a high amplitude and short rise-time along with sharp increase of discharge current and uniform preionization allow to form long-lived stable volume discharge in halogen containing gas mixtures. UV laser pulses with total duration up to 450 ns were easily obtained. Another way for development of a long-lived diffuse plasma was suggested. Diffuse discharge was formed in a sharply inhomogeneous electric field by run-away electrons when using high voltage pulses of ns duration Efficient VUV lasing was obtained at wavelengths from 148 to 193 nm on the transitions of hydrogen, fluorine and exciplex ArF* molecules in mixtures of rare gases with additions of hydrogen and fluorine at pressures up to 10 atm.
The results of the formation and amplification of positive chirped 0.1 ns laser pulse at a central wavelength of 470 nm in the laser system THL-100 are presented. It is shown that a front-end allows forming a radiation pulse with a Gaussian intensity profile and the energy up to 7 mJ. At amplification in XeF(C-A) amplifier of the pulse with 2-5 mJ energy a saturated mode is realized and 3.2 J output laser beam energy is reached.
Results of 2D simulation of a KrF laser are presented. In the model, inhomogeneities of distributions of the electric field and plasma particle concentration are considered. It is demonstrated, that the laser energy depends not only on the value of the total pump power, but also from its spatial distribution. The shape of the electrodes is a major determinant of the spatial distribution of pumping power in the active medium. For electrodes with small radii of curvature, the pumping power in the center of the discharge may be too high. This leads to the suppression of radiation in the center of the discharge and the limitation of the laser energy.
Evolution of spatial and energy characteristics start pulse with energy of 0.8 mJ in duration of 2 ps in the XeF(С-A) amplifier of THL-100 laser system have been studied experimentally and by numerical simulation. Laser radiation energy E = 2 J was obtained experimentally. In that work we present the 3D-model amplification of conically diverging laser beams, that takes into account the spatial inhomogeneity of the pump, and the geometry of THL-100 laser system amplifier. Description and the test results of the model are submitted. At the start pulse energy 0.8 mJ, the calculated radiation energy at the XeF(С-A) output reaches 2.4 J. Simulation results shows that, maximal intensity of the laser radiation in this mode reaches P = 60 GW/cm2. The evolution of the energy and space-time structure of the laser beam in the amplifier was investigated. It is shown that in the ideal case (excluding the processes of nonlinear interaction of laser beam with an active medium), at the start pulse energy of 5 mJ, the energy of the laser radiation at the output of the amplifier is increased to Eout = 3.8 J. In this mode, the maximal radiation intensity reaches a value of I = 148 GW/cm2.
Results of experimental measurements and numerical simulations of the N2 and XeF2 gas pressure effects on the gain characteristics are presented in the paper. It is experimentally and theoretically is shown that maximum total gain (5-6)×104 achieved at a pump energy E = 240 J, 0.2 Torr XeF2 and 0.5 atm N2 pressure. Increasing and decreasing of N2 pressure leads to decrease of the gain. The possibility of the XeF(C-A) amplifier operation in a generator mode is discussed and the theoretical study results of generation are presented. It is shown that an annular laser radiation with energy up to 8.5 J can be obtained. The study results of the influence on the laser energy of N2 and XeF2 pressure and reflectance coefficient of output mirror are presented.
Terawatt hybrid (solid state/gas) laser (THL-100) system on the basis of Ti:sapphire starting complex (50 fs, 5 mJ)
and photochemical XeF(C-A) amplifier with the aperture of 24 cm is presented. Laser system is built at Institute of High
Current Electronics SD RAS, Tomsk, Russia. The design and peculiarities of optical pumping of XeF(C-A) amplifier,
methods of pump power measuring, gain distribution across the active volume are discussed. The results of numerical
modeling of the output parameters simulation are presented and one compared with first experimental results.
Terawatt hybrid laser (THL-100) system on the basis of Ti:sapphire starting complex and final amplifier with
gaseous optically driven active media on XeF(C-A) molecules is presented. Laser system is built at Institute of High
Current Electronics SB RAS, Tomsk, Russia. It consists of Ti:sapphire starting complex and photochemical XeF(C-A)
amplifier. The active media of amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length. The results
of numerical modeling of the output parameters and first experimental results are presented in this paper.
An interest to properties of the discharge in gas mixtures with SF6 is justified by a wide use of such mixtures in the electron and commutation apparatuses and in the pulse discharge HF/DF lasers. Such lasers are considered to be perspective sources of radiation in the 2.4-3.2 μm range of the wave lengths. Experimental studies of the discharge in mixtures Ne/SF6/C6H14 [1] and SF6 - C2H6 [1, 2] have shown, that under certain conditions the discharge area extends, and spreads over the whole surface of electrodes. Discharge in the pure SF6 (P = 78 mBar) [3] was shown to expand in width from ~ 2.5 mm to ~ 3.5 mm. The mechanism of such an expansion till now remains unclear. The present paper is devoted to computer modeling of kinetic processes in non-uniform plasma in the SF6 gas. The kinetic processes affecting temporal and spatial distribution of the current density in non-uniform plasma are revealed.
A number of unique properties of the electric-discharge XeCl laser, like possibility to generate laser pulses with duration from single nanosecond to hundreds ns, continues to attract a research interest to that laser system. It follows from an analysis of the laser characteristics obtained by different groups throughout the world [1], conditions of the laser generation to a great extent influence the output laser characteristics. The highest laser efficiency of 4-5% with the specific radiation energy 2-3 J/l is achieved at the pulse durations of 200-100 ns and pumping power of ~0.5 MW/cm3. Laser regimes characterized by high radiation energy of 7-10 J/l, but lower efficiency of 1-3% has been realized at a pulse duration of ~50 ns and pumping power of 2-10 MW/cm3. An increase of the radiation power becomes possible in regimes with a short pumping pulse of 30-20 ns, but at the cost of the laser efficiency, which decreases to 2-3%. The aim of the present work was a search of some general (independent on the pumping regimes) relationships, which could be used as a guideline for the choice of the initial conditions for creation of lasers with desirable parameters. Computer modeling was used as a research method, since it allows to a full extent explore the relation between the output characteristics of a laser and the initial conditions.
Results of experimental and theoretical investigations of discharge XeCl laser with 35 ns (FWHM) radiation pulse
duration are presented. Laser generates the laser pulse energy of O.6 J with 2% total electric efficiency and 100 Hz pulse
repetition rate. Calculated laser radiation parameters and discharge parameters have a good agreement with experimental
results. Influence of basic plasma-chemical processes in discharge on laser output and efficiency is shown. Maximal
laser efficiency relatively pumping power was 3.5%.
Results of experimental and theoretical investigations of discharge XeCl laser with 30 ns (FWHM) radiation pulse duration are presented. Laser generates the laser energy of 0.35 J with 2.2% total electric efficiency. Calculated laser radiation parameters and discharge parameters have a good agreement with experimental results. Influence of basic plasma-chemical processes in discharge on laser output and efficiency is shown. Maximal laser efficiency relatively pumping power was 3.7%.
This paper presents simulation results for three modes of pumping of a XeCl-laser under radiation pulse duration of 10, 30, and 50 ns. Temporal evolutions of pump power and laser radiation, energy of pumping and lasing, densities of electrons and HCI(i) molecules in the ground and vibrationally excited states have been simulated for each mode. Rate dependences ofthe processes of XeCl** excimer molecules formation, such molecules quenching by electrons and heavy
particles of plasma N(i), and induced radiation rate vs. time have been also obtained. For two modes of pumping with radiation durations of 30 ns and 50 ns, simulation data are compared with experimental results taken from the literature available. The simulated temporal evolutions of discharge current, radiation power, and lasing energy are in good agreement with the experimental results. There are no literature data regarding a laser with a pulse duration of 10 ns. The properties of laser operation at decreased pumping duration up to 10 ns are presented. Kinetic processes effect on radiant energy and laser efficiency has been analyzed. It follows from the analysis of calculation results that formation of excimer molecules takes place with high efficiency. Quenching processes of excimer molecules by electrons and heavy particles is the main factor leading to decrease in radiant energy, and therefore laser efficiency.
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.
This paper reports on experimental results and simulation of XeCl-laser with short laser pulse duration. Experimental investigation was aimed at obtaining of maximal lasing power and efficiency. The processes taking place in plasma and in resonator were simulated. Temporal evolutions of plasma particle density as well as simulation rates of processes of ionization, recombination, attachment and formation of XeCl molecules in excited states were obtained. Simulation dependencies have been analyzed; mechanisms of initial parameter effect on lasing power have been established.
Present paper reports the results of theoretical investigations of influence of Q-factor value of optical resonator on spatial properties and output characteristics of long pulse discharge pumped XeCl laser. It has been shown that high value of Q-factor do not influence homogeneity of discharge plasma. When the value of Q-factor is low an inhomogeneous distribution of intensity of laser photon flux occurs already at the beginning of generation. Photoionization of excited Xe atoms leads to an enhancement of electron density near the output mirror in comparison with the rest discharge volume. Further development of inhomogeneity is caused by instability of discharge plasma. Inhomogeneity of pumping discharge initiated by interaction between laser photon flux and discharge plasma leads to significant changes of characteristics of laser radiation.
Dynamics of development of single hot spot discharge in SF6 gas and in the mixture SF6/C2H6 and of its contraction has been studied experimentally. Visualization of discharge development has been performed by a fast shutter CCD camera. Discharge properties have been studied in a wide range of current densities and input energies. It has been found that a single hot spot discharge has a cup- like structure. The diameter of the cathode hot spot is 0.04 cm, while the diameter of the plasma near the anode reach a value of about 3 cm. An increase of the discharge current causes an enlargement of the discharge cross section. The hypothesis of discharge widening is presented and discussed. It has been shown that discharges in the mixture are more homogeneous and stable. Single hot spot allows to realize a discharge current of 2 - 3 kA at input energies of about 1 - 3 J without distortion of discharge homogeneity. When the discharge with three hot spots separated by 5 mm has been investigated, the formation of inhomogeneity from one hot spot occurs at 700 A. Development of a channel with enhanced conductivity from single hot spot in SF6 gas has been also obtained experimentally in case with advanced preionization.
Results of experimental and theoretical investigations of XeCl with discharge formation by means of inductive energy storage and semiconductor opening switch have been presented. Main pumping of active medium has been performed by capacitive energy storage. Measured laser output energy is 0.8 J Laser efficiency calculated from energy stored in capacitive energy storage is 2.3%. Simulations predict that the optimization of pumping conditions may increase these parameters in two times.
Effect of the border of preionization on discharge uniformity and quality of laser radiation is studied theoretically in the framework of 2D model of discharge pumped XeCl laser. Calculations show that near the border between preionized and unpreionized regions a local enhancement of the electric field occurs. This phenomenon is induced by a divergence of the X-ray beam. The local enhancement of the electric field promotes formation of cathode spots and, finally, leads to formation of discharge inhomogeneities. A decrease of sharpness of the border of preionization region reduces the local enhancement of electric field and improves characteristics of the laser radiation.
KEYWORDS: Optical amplifiers, Laser systems engineering, Oscillators, Diffraction, High power lasers, Gas lasers, Excimers, Molecules, Optical components, Amplifiers
High power XeCl laser system and experimental results of diffraction limited laser beam amplification are described. Beyond the preamplifier, the 5 cm X 6 cm laser beam contained 50% of the radiation energy in the diffraction core. At the output from the system an irradiation brightness of 2 X 1014 W/cm-2cr-1 was obtained. Minimum divergence near 0.05 mrad of output beam was restricted to turbulence of air and optics elements. A numerical model of the amplification of the radiation, taking onto account the influence of the amplified spontaneous emission, was developed.
Results of experimental and theoretical investigations of a homogeneous discharge in SF6 gas have been presented. Experiments with use of electrodes made of Al have clarified that even by small current densities (below 20 A/cm2) and pulse durations (50 ns) the cathode surface is covered by a number of hot spots, which influence discharge homogeneity and stability. The hot spot density of about 10 cm-2 is found to be necessary for ignition of a homogeneous discharge. In order to achieve desirable hot spot density special kinds of cathodes with predefined hot spot number have been designed. These cathodes have provided high discharge homogeneity and stability.
The pumping discharge of XeCl laser was modeled, taking into account the main kinetic processes. The inhomogeneity was set on the cathode, both as local enhanced density of the initial electrons, and as a metal hemisphere. It is shown, that the plasma channel with high conductivity is formed from the initial inhomogeneity in the discharge.
An electric-discharge-pumped XeCl laser using phototriggering by x rays is described. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a 4-l active volume with an efficiency of about 2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A uniformity analysis of the discharge pumping has been made for the XeCl laser.
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