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.
Discharge and laser parameters in high-pressure gas mixtures of rare gases with F2 under pumping by generators with inductive energy storage (IES) and semiconductor opening switch (SOS) are studied. It was shown that the pre-pulse with high pumping power formed by IES produces high-density discharge plasma and inversion population in gas mixtures under study within ∼10 ns and provides both early one-set of lasing and conditions for efficient excitation of an active medium from the storage capacitor. The high-voltage pre-pulse from the IES and sharp increase of discharge current allows to form long-lived stable volume discharge. Improve of pulse duration and (or) output energy was achieved for atomic fluorine, ArF* and KrF* excimer lasers.
Experimental study and theoretical analysis of growth of microstructures (microtowers) on liquid metals by fs laser pulses have been carried out. Theoretical analysis has been performed on the basis of the two-temperature model. Compared to ns laser pulses, in fs irradiation regimes the heat-affected zone is strongly localized resulting in much larger temperatures and temperature gradients. In the experimental irradiation regimes, the surface temperature of liquid metals studied may reach or even exceed a critical level that culminates in phase explosion or direct atomization of a metal surface layer. However, before explosive ablation starts, a stress wave with an amplitude up to several GPa is formed which demolishes oxide covering. Moreover, at high laser fluences laser-induced breakdown is developed in oxide layer covering the metal surface that leads to destruction/ablation of oxide without damaging metal underneath. An overall scenario of microstructure growth with fs laser pulses is similar to that obtained for ns irradiation regimes though the growth threshold is lower due to smaller heat-conduction losses. Also we managed to obtain microstructures formation by the action of spark discharge.
VUV radiation of run-away electron preionized discharge (REP DD) in different gas mixtures is studied. Efficient lasing was achieved on ArF* (193 nm) and F2* (157 nm) molecules. Narrowband VUV radiation (near 147 nm), corresponding to the optical transition of a heteronuclear dimer ArXe*, was recorded from the REP DD plasma in (He)-Ar-Xe mixture. Amplifying properties of the discharge plasma related to this radiation were found.
Laser action in run-away electron preionized discharge (REP DD) was studied. Efficient laser emission was obtained in wide spectral range from IR to VUV. It was shown that ultimate efficiency of non-chain chemical lasers on HF (DF) molecules and N2 laser at 337.1 nm can be achieved in REP DD. New mode of N2 laser operation with 2 or 3 peaks in successive REP DD current oscillations was found. Efficient lasing on KrF* and XeF* excimer molecules with parameter close to laser parameters of lasers pumped by conventional transverse discharge were demonstrated for the first time. Laser action on F2* at 157 nm and rare gas fluorides under REP DD pumping was obtained for the first time, as well. The efficiency and pulse duration of VUV F2* laser under REP DD excitation are comparable with those obtained in transverse discharges with preionization. VUV emission of REP DD in binary and ternary Ar-Xe-(He) and Ar-Kr-(He) mixtures at wavelength close to 147 nm was measured. Possibility of VUV lasing in mixtures of rare gases is considered.
Formation features of run-away electron preionized diffuse discharge (REP DD) and REP DD properties in different experimental conditions are studied. It was shown that sufficient uniformity of REP DD allows its application as an excitation source of lasers on different gas mixtures at elevated pressure. Promising results of REP DD application for development of gas lasers are shown. Stimulated radiation in the IR, visible and UV spectral ranges was obtained in the diffuse discharge. Ultimate efficiency of non-chain HF(DF) chemical and nitrogen lasers on mixtures of SF6 with H2(D2) and N2 was achieved. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at λ = 337,1 nm. Long-pulse operation of rare gas halide lasers was achieved.
It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of gas mixtures at elevated pressures and can produce laser emission. We report experimental and simulated results of application of the REP DD for excitation of different active gas mixtures. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing predicting the radiation parameters of nitrogen laser at 337.1 nm. Peculiarities of the REP DD development in different gas mixtures are studied, as well. It was shown that the REP DD allows obtaining efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Laser action on N2, HF, and DF molecules was obtained with the efficiency close to the limiting value. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.
It was shown that run-away electron preionized volume (diffuse) discharge (REP DD) can be used as an excitation source of active gas mixtures at elevated pressures and can produce laser emission. We report experimental and calculated results of application of the REP DD for excitation of different active gas mixtures. It was shown that the REP DD allows to obtain efficient lasing stimulated radiation in the IR, visible and UV spectral ranges. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at 337.1 nm. Promising prospects of REP DD employment for exciting a series of gas lasers was demonstrated. Lasing was obtained on molecules N2, HF, and DF with the efficiency close to the limiting value. It was established that the REP DD is most efficient for pumping lasers with the mixtures comprising electro-negative gases.
Generators with inductive energy storage (GIES) are developed for laser application. Discharge and laser parameters in
high-pressure gas mixtures are studied. It was shown that the IES generator produces high-voltage pre-pulse and sharp
increase of discharge current which allows to form long-lived stable discharge in different gas mixtures. Improve of both
pulse duration and output energy was achieved for XeCl-, XeF- and KrF excimer lasers. Maximal at that date radiation
power, output energy and laser pulse duration of N2 laser were obtained. Efficient operation on CO2 molecules with high
peak power was demonstrated. Ultimate efficiency of HF(DF) non-chain lasers was achieved.
Formation of stable micro-protrusions and microstructures ("microtowers") on surface of liquid metals during
multipulse irradiation by UV and IR lasers in different ambient gases was discovered. The rates of the structure
formation have been measured which can reach 5 - 20 μm/pulse depending on the metal and ambient gas sort. Single
micro-protrusions 1-2 mm in length were formed with diameter approximately two times greater than the focal spot
size. The possibility to control the microstructure shape is shown and their potential applications are demonstrated.
We report a new phenomenon, formation of microstructures, observed at multipulsed nanosecond laser ablation of liquid
metals (Ga, In, Sn-Pb alloy, Wood's metal). Laser irradiation of liquid metal targets was carried out in a gas chamber
equipped with a heater. In contrast to vacuum conditions or an inert atmosphere when a crater is formed which is healed
after termination of irradiation, ablation in a reactive ambient gas (air, nitrogen, sulfur hexafluoride, nitrogen trifluoride)
leads to a horn-like structure growing on the irradiated surface with the rate of 3-20 μm per pulse depending on laser
fluence and the types of metal and ambient gas. The interplay between different processes in a heat-affected zone of the
irradiated samples is analyzed, including ablation, thermal expansion, temperature variations of viscosity, surface
tension, thermal stresses, capillary and plasma effects, and surface chemistry. A clear picture of microstructure origin has
been established and a qualitative modeling representation is given to explain the growth process of microstructures. The
optimal conditions of microstructure growth have been determined and perspective applications of the discovered effect
are discussed.
Experimental and theoretical studies on laser ablation of polymers (PMMA, polyimide) have been performed in a wide
range of CO2-laser fluences. Evolution of polymer laser plume in air has been investigated with simultaneous
registration of radiation spectra of the ablation products, spatial dynamics of plasma flare, and temporal behavior of
plasma emission on separate spectral lines. It has been found that spectral lines have intensity peak after laser pulse
termination while plasma emission spectra are similar to those of organic material combusting. The results confirm that
combustion of the laser-vaporized polymers occurs in the plasma plume. A thermo-chemical model of heating and
ablation of organic polymers by CO2 laser pulses has been developed which takes into account attenuation of radiation in
laser plasmas and chemical processes leading to heating the plume of the ablation products. Temperature evolution in the
irradiated sample, ablation dynamics, and laser beam attenuation are analyzed. The modeling results are compared with
the experimental data on high-speed imaging of the plasma plume. The effect of the formation of a "plasma pipe" is
revealed under polymer ablation in air under normal conditions.
Review on application of double-discharge circuits with inductive energy storage (IES) and semiconductor opening
switch (SOS) for development of efficient gas lasers is presented. It was shown that the IES allows to form long-lived
stable discharge in different gas mixtures. As a result, pulse duration, output energy and efficiency of the lasers under
study were improved.
Laser and discharge parameters in mixtures of rare gases with halogens driven by a pre-pulse-sustainer circuit technique
are studied. 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 UV- and x-ray preionization allow to form long-lived stable discharge in halogen
containing gas mixtures. Improvement of both pulse duration and output energy was achieved for XeCl-, XeF-, KrCl-
and KrF excimer lasers. Maximal laser output was as high as 1 J at efficiency up to 4%. Increase both of the radiation
power and laser pulse duration were achieved in N2-NF3 (SF6) and He-F2 (NF3) gas mixtures, as well.
We report development of long-pulse discharge N2-lasers pumped by inductive energy storage with maximal radiation
parameters. The laser output from an active volume with cross-section up to 6×10 cm2 was as high as 110 mJ with peak
power of about 6 MW. In mixtures of nitrogen with NF3 laser pulses about 100 ns in duration were obtained. Numerical
model of nitrogen laser on mixtures of nitrogen with electronegative gases pumped by transverse discharge is developed. This model allows to simulate laser parameters on transition C3Πu → B3Πg and predict the laser operation in different experimental conditions.
Laser and discharge parameters in mixtures of rare gases with halogens driven by a pre-pulse-sustainer circuit technique
are studied. 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 UV- and x-ray preionization allow to form long-lived stable discharge in halogen
containing gas mixtures. Improvement of both pulse duration and output energy was achieved for XeCl-, XeF-, KrCl-
and KrF excimer lasers. Maximal laser output was as high as 1 J at efficiency up to 4%. Increase of the radiation power
and laser pulse duration was achieved in N2-NF3 (SF6) and He-F2 (NF3) gas mixtures, as well.
Spectral, energy and temporal parameters of a pulsed discharge in xenon are studied. It is shown that the use of unidirectional current pulse instead of oscillating one improves radiation power in the range 200-350 nm, while duration of the radiation pulse at half-maximum decreases. The use of SOS-diodes in the pulse generator allows obtaining the maximal radiant intensity 64 kW/sr in the range 200-350 nm and the pulse duration of ~2 μs FWHM.
Laser and discharge parameters in mixtures of rare gases with halogens driven by a pre-pulse-sustainer circuit technique are studied. 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 UV- and x-ray preionization allow to form long-lived stable discharge in halogen containing gas mixtures. Improve of both pulse duration and output energy was achieved for XeCl-, XeF- and KrF excimer lasers. Maximal laser output was as high as 1 J at intrinsic efficiency up to 4%. Increase of radiation power and laser pulse duration were obtained in N2-NF3 (SF6) and He-F2 (NF3) gas mixtures, as well.
The studies devoted to free-expanding and bounded discharges, taking place in a Xe flashlamp, have been carried out. With such a discharge bounded by the walls of a bulb the maximal UV radiation power density was ~ 700 kW/cm2 on the internal surface ofthe bulb and ~ 380 kW/cm2 on its external surface.
Discharge and laser parameters in mixtures of SF6 with H2 and D2 are studied using inductive and LC-generators.
Excitation pulse parameters providing ultimate performance of discharge non-chain HF- and DF-lasers are determined.
Processes affecting efficiency of the lasers are discussed. Ultimate intrinsic efficiency ηint of the HF and DF lasers up to
10 % and 7%, respectively, was realized in the SF6-H2 (D2) mixtures. Electrical efficiency of the lasers up to η0 =6,4%
with the output up to 1,5 J was demonstrated for the first time.
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 ηin=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 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.
A four-stage XeCl laser system named Photons has been developed for studying laser interaction with materials. The Photons are outlined and preliminary results characterizing the system are given. The master oscillator Photon-1 can provide “seed” light with laser energy of about 40mJ, pulse duration of about 250ns and good beam quality of nearly diffraction-limited divergence angle and narrow line width less than 1 cm-1 for whole system. The output energy of laser system of 251J has been obtained by four-stage amplification. The synchronization among five lasers is realized by the combination of low voltage timer, high voltage synchronic generators and compensated cables. The demonstration shows Photons good operation with low jitter of less than ±20ns.
Discharge and laser parameters in mixtures of SF6 with H2 and D2 are studied using inductive and LC-generators. Excitation pulse parameters providing ultimate performance of discharge non-chain HF- and DF-lasers are determined. Processes affecting efficiency of the lasers are discussed. Ultimate intrinsic efficiency ηint of the HF and DF lasers up to 10% and 7%, respectively, was realized in the SF6-H2 (D2) mixtures. Electrical efficiency of the lasers up to η0 = 5-6% with the output over 1 J was demonstrated for the first time.
Diamond radiation detectors (DRDs) operate on the principle of photoconductive response of the normally insulating, Type IIa diamond when dosed by electromagnetic radiation or high energy particles. As detectors, they offer fast response (~100 ps) and can handle high radiation doses (~1 GGy) without degradation. Diamond also offers significant advantages over semiconducting materials as a compact, bi-polar, high voltage switching medium because of its high dielectric strength and thermal conductivity. However, the wide band-gap of diamond and its normally insulating state impose stringent requirements on the trigger radiation that is used to make the diamond conductive. This paper describes a simple model for conduction in diamond, and compares this model with experimental conductivity as measured in a natural diamond Type IIa radiation detector that was irradiated by laser excitation at various wavelengths from 222-353 nm. The DRD geometry consisted of a 3x1x0.5 mm3 Type IIa diamond with metallization on the 3x0.5mm2 sides. The DRD was exposed to laser light in the orthogonal 3x1 mm2 plane. Agreement with the measured data is achieved by fitting a parameter (defined here as β) at the various irradiation wavelengths. This fitting parameter is itself a function of two physical quantities: α, the absorption coefficient of the diamond and εo, the ionization cost to produce a hole-pair. Using published values of α, we deduce values of εo and compare them with published values for Type IIa diamond in the deep UV to soft x-ray regions. This model also provides a basis for design of high voltage diamond switches that are triggered by near-bandgap (220-250 nm) UV radiation.
Development of a long-pulse spark preionized XeCl-lasers pumped by a self-sustained discharge using a double-discharge circuit is reported. The pre-pulse is formed by novel generator with an inductive energy storage and semiconductor opening switch. The lasers produce up to 1-1.5 J in a pulse with total duration up to 500 ns and total efficiency up to 1.5-2%. Circuit for the discharge current correction is suggested for further extension of the optical pulse. The laser producing 300 ns (FWHM) was used as a master oscillator in a powerful XeCl-laser system.
Effect of pumping pulse duration and specific input energy on the output 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- and DF-lasers are determined. High discharge uniformity obtained with the use of special shaped electrodes along with uniform UV preionisation was found to be key parameter for improving efficiency of discharge HF (DF)-laser. Intrinsic efficiency of HF and DF lasers up to ηin~10 % and 7%, respectively, is obtained in the SF6-H2(D2) mixtures. With the LC-generator, maximal total efficiency of the lasers up to η0=6% was obtained and the output over 1 J was realized.
Pulse repetitive generators with inductive energy storage unit and semiconductor opening switch were developed and used for pumping lasers on CO2, N2, Cu vapor laser and VUV Xe excilamp. For the first time, operation of the generators at pulse repetition rate up to 100 kHz has been realized. Improvement of the laser and excilamp output parameters were achieved.
Laser action and discharge in gas mixtures of SF6 with hydrogen, deuterium and hydrocarbons are studied. Non-chain HF lasers with specific output energy of 8,8 J/1×atm (140 J/ 1×atm) and DF-laser with output of about 1 J pumped by LC-generators were developed. HF laser efficiency with respect to deposited energy of 10 % was obtained for the first time using inductive and LC-generators.
Amplitude-temporal and spectral paramters of laser radiation and electric discharge parameters in gas mixtures of SF6 with hydrogen and hydrocarbons in the high efficiency operation mode are studied. The laser effiency with respect to deposited energy up to ηdep ~10% is obtained using both inductive and capacitor generators. It was shown that maximal efficiency of the HF-laser is reached under high E/p parameter value across the laser gap during excitation pulse (where E is the electric field strength, p is the gas mixture pressure). Application of profilated electrodes along with UV preionization allows to obtain specific output of the non-chain HF-laser of about 140 J/l×atm and total laser efficiency η0~4.5%. It was found that output spectra of the laser in the high efficiency operation mode significantly widen and cascade laser action on some rotational lines of HF molecule vibrational transitions v(3-2) → v(2-1) → v(1-0) is observed.
Amplitude-temporal and spectral parameters of laser radiation and electric discharge parameters in gas mixtures of SF6 with hydrogen and hydrocarbons are studied. Experimental conditions providing high intrinsic efficiency of a non-chain HF laser are determined. The laser efficiency with respect to deposited energy up to ηin ~ 10% is obtained using discharge excitation by inductive and capacitor generators in SF6-H2 mixtures. High discharge uniformity obtained with the use of special shaped electrodes along with uniform UNV preionization is key parameter for improving intrinsic efficiency of discharge HF-laser. There with output spectra of the HF laser significantly widens and cascade laser action on some rotational lines of the vibrational transitions of HF molecules v(3-2) → v(2-1) → v(1-0) is observed. Specific output of the non-chain HF-laser over 8 J/l (140 J/lxatm) and total laser efficiency η0~4,5% were achieved, as well.
Development of long-pulse discharge XeF- and KrF-lasers pumped by a generator with an inductive energy storage and semiconductor-opening switch is reported. It is shown that use of inductive storage element allows significantly improve discharge stability and expand laser pulse duration. Pulse duration (FWHM) of 60 ns was obtained both in Ne-Xe- NF3 and Nr-Kr-F2 gas mixtures. Laser specific output of 2,5 J/l and intrinsic efficiency over 1% have been obtained for KrF laser.
The present work reports development of simple, reliable, powerful pseudospark switches. Operating parameters of the switches and parameters of XeCl-lasers with pumping generators on the base of the switches are presented.
Development of a long-pulse master oscillator with pulse duration of 300 ns (FWHM) is reported. The oscillator is made on the base of a long-pulse spark preionized XeCl-laser pumped by a self-sustained discharge using a double- discharge circuit. The pre-pulse is formed by a generator with an inductive energy storage and a semiconductor opening switch. The laser produces up to 1,5 J in pulse with total duration up to 450 ns.
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.
The results of investigation into the use of UV-laser produced plasma for high-current commutation are summarized. It is shown that exciplex lasers can be used as efficient triggers for megavolt gas switches. If the laser spark length is comparable with the switch gap, the triggering delay time and jitter are independent on the arc position in the gap. In other cases, the shortest delay time was observed under focusing on the electrode surface. The plasma formed by exciplex lasers on the metal targets has been studied. The plasma formation thresholds and plasma expansion velocities have been measured.
An efficient electric-discharge XeCl laser is developed, which is pumped by a self-sustained discharge with a pre-pulse formed by a generator with an inductive energy storage and a semiconductor opening switch on a basis of SOS diodes. An output energy up to 800 mJ, total pulse length up to 450ns, and a total laser efficiency of 2.2% were attained using a spark UV preionization.
In the present report, plasma formed on the surface of metals and dielectric materials under the action of XeCl and KrCl lasers is studied. Plasma formation thresholds and plasma expansion velocities are measured. It was shown that long-lived plasma objects are formed near a target in the atmosphere of Xe or air at pressure 0.1 - 1 atm. Duration of luminescence of the plasma objects was maximal in xenon. Non-symmetric current passing through the laser plasma and the current interruption were obtained. The interruption time was as short as 10 ns while the plasma resistance increases with the rate up to 1010 Ohm/s. It is shown that the interruption rate increases when plasma of elements with small atomic weight is used and at higher rice-time of the current before its interruption. It was found that the plasma ionization degree is saturated before the interruption. The interruption effect was used for development of generators with inductive energy storages. Generator with a plasma erosion opening switch with opening current of 10 kA operating at pulse repetition rate up to several Hz was used for excitation of pulsed lasers. Using the generator, laser action on nitrogen and XeCl molecules and atomic transition of Ne was obtained.
Investigation was made ofthe characteristics ofXeCl (λ ~ 308 nm), KrC1 (λ ~ 222 nm) and Xci (λ ~ 253 nm) capacitive discharge excilamps. High efficiency of exciplex molecules and simple design have been obtained under capacitive HF discharge excitation. Cylindrical excilamps with radiation output through side surface ofthe cylinder and through one or two windows placed on the tube ends have been developed. High UV radiation power and electrical power deposition to fluorescence conversion resulted in efficiencies of up
to 12%. The study of XeC1, KrCl and XeI excilamps have shown, that it is possible to create sealed-off samples with lifetime more than 1000 hours. The stability of output parameters ofthe capacitive discharge excilamps is studied and the mechanism of chlorine losses in low pressure halogencontaimng excilamps made of quartz was determined.
The possibility of creation of capacitive discharge excilamps with short pulse duration was studied. In capacitive discharge cylindrical KrClexcilamp, at λ~222 nm the radiation pulse power up to 2.5 kW was obtained. Powerful radiation pulses 50 ns in duration were obtained at pulse repetition rate of 1 kHz.
The present paper reports the experimental results and design of the laser systems developed for lidar experiments. The laser systems with radiation energy of hundreds of millijouls at each of several wavelengths allow to detect NO2 and SO2 atmospheric impurities. At the moment the laser system: powerful XeCl*-laser-dye laser is incorporated in a lidar developed at the Scientific Research Institute of Space Equipment (Moscow) for measurements of NO2 content in the atmosphere.
In the recent years, great progress in development of spontaneous UV and VUV sources, radiating on the transitions of excimer and exciplex molecules has been achieved. However, practical use of sealed-off excilamps is limited by low lifetime of gas mixture. In this paper, stability of output parameters of the excilamps pumped by glow, barrier and capacitive discharges is studied and the mechanism of chlorine losses in low pressure halogen containing excilamps made of quartz is determined.
Generators with inductive energy storage units and semiconductor opening switches designed for laser excitation are described. Operation of the generators on gas-discharge load is considered and possible excitation modes are discussed. Longitudinal N2-laser with inductive energy storage unit and semiconductor opening switch is investigated. It is shown that pumping by inductive energy storage unit reduced the influence of the discharge circuit inductance and broadened the range of the operating pressures at which lasing was possible. Besides the laser output energy may be increased by means of peaking capacitors connected in parallel with a discharge tube. Transverse discharge non-chain HF-laser and C02-laser are developed basing on this pumping technique. Output energy of 0,6 J and 3,2 J and the laser efficiency of 5,5% and over 17% were demonstrated on H2-SF6 and He-CO2-N2 gas mixtures, respectively. High laser parameters obtained demonstrate considerable promise of such inductive generators for pumping different gas lasers.
KEYWORDS: Electron beams, Halogens, Diodes, Hydrogen fluoride lasers, Monte Carlo methods, Laser energy, Pulsed laser operation, Mirrors, Gas lasers, Chemical reactions
The results are presented of experimental and theoretical investigations of excitation and generation of the HF laser pumped by nonchain chemical reaction initiated by a beam of electrons as well as of the KrF and XeCl lasers pumped by beams of electrons. The effect of the volume charge field on the distribution of energy over the cross section of a laser cell and of the radiant energy density over the cross section of an output laser beam in mixtures with different concentrations of halogen is analyzed. The output energy density distribution over the beam cross section for lasers excited by the radially convergent beam of electrons and the total pump energy are determined. The pump energy distribution over the laser cell cross section and the total pump energy in various gas mixtures are calculated.
The results of the experimental study of UV and IR lasers pumped by various methods are presented. The accelerators with radially converging or planar e-beams pumping gas mixtures at pressures up to 3 atm and self-sustained discharges were used. The highest laser radiation energies in the UV up to 2 kJ have been obtained at (lambda) equals 308 nm. Output of 100 J at (lambda) equals 1.73 micrometer in Ar-Xe mixture and 50 J at (lambda) equals 2.03 micrometer in He-Ar-Xe mixture was obtained from the e-beam laser with active volume of 600 l. Output energies of 110 J at (lambda) equals 308 nm and 90 J at (lambda) approximately 250 nm, respectively, were achieved in compact high-power e-beam laser with chamber of 20 cm in diameter and 30 l active volume. This e-beam geometry was shown to be very promising for excitation of non-chain HF- laser media. HF-laser efficiency with respect to deposited energy as high as approximately 10% and energy up to 200 J at (lambda) approximately 2.8 micrometer were demonstrated. Amplification of XeCl-laser beam from master oscillators and amplifiers under conditions of strong amplified spontaneous emission is considered. Investigations of CO2 laser excited by e-beam controlled discharge and e-beam ignited discharge were performed. The highest laser output in the IR of 3 kJ have been obtained at (lambda) equals 10.6 micrometer.
Operating parameters of powerful excilamps with different discharge geometry pumped by glow discharges, high-pressure volume discharge with UV-preionization and barrier discharge are presented. Intense radiation of Ar2*, Kr2*, Xe2*, ArF*, KrBr*, Cl2, KrCl*, KrF*, XeI*, XeBr*, XeCl*, XeF*, I2 and IBR molecules was obtained in rare gas or in rare gas -- F2 (CH3Br, Cl2, HCl, I2, NF3) mixtures. Excilamps with high spatial uniformity of the output, narrow emission line and high gas life-time were developed. It was shown that efficiency of luminescence of exciplex molecules KrCl* of about 30% can be obtained in high- voltage glow discharge and positive column of glow discharge. Output at (lambda) approximately 222 and 308 nm up to 200 W from single excilamp and 500 W from three excilamps operating in parallel was demonstrated. It was shown that the efficiency of barrier discharge excilamps pumped by sinusoidal pulses several tens microseconds in duration can be sufficiently improved.
The present report describes gas lasers pumped by generators with inductive energy storage and semiconducting opening switch. It is shown that these generators significantly improves output parameters of different gas lasers. Longitudinal small-scale N2 laser and CO2 and non- chain HF transverse discharge lasers are developed using this pumping technique. Efficiencies of CO2 and HF lasers up to 17% and 5,5%, respectively, were demonstrated. Advantages of generators with inductive energy storage are discussed.
Excilamps with different tube geometry pumped by continuous glow and barrier discharges are described. It was shown that the efficiency of barrier discharge excilamps pumped by sinusoidal pulses with duration of several tens microseconds can be sufficiently improved. The range of UV wavelength emitted by glow discharge excilamps was extended. Intense radiation of KrBr*, XeBr*, I2* and IBr* molecules was obtained in rare gas - CH3Br (I2) mixtures pumped by glow discharge KrCl* excilamp ((lambda) approximately 222 nm) with output power up to 200 W was developed. UV power of 500 W from three KrCl* excilamps operating in parallel was demonstrated. Efficiency of exciplex molecule luminescence in the positive column of glow discharge was found to be as high as approximately 30%.
Novel single block process facility including UV excilamp and sources of atomic hydrogen is described. Circular sealed-off KrCl* excilamp emitting two intensive bands at 195 and 222 nm was used. The source of atomic hydrogen on the base of reflecting Penning arc discharge was placed in line with the lamp. Semiconducting structures were treated in an expanding effusion jet of atomic hydrogen. The possibility to realize the process of cleaning GaAs surface under joint action of atomic hydrogen and UV radiation has been investigated. Effect of UV radiation on the rate of removing oxide layer is found at low temperature (18 - 100 degree(s)C). The mechanism providing an explanation for this event is suggested. The possibility to realize GaAs surface cleaning using successive performing the procedures of the surface treatment by atomic hydrogen, its oxidation with UV- stimulation and additional treatment by atomic hydrogen was also studied. The sources of atomic hydrogen and UV radiation developed allows to improve cleaning control and provides a way of producing the surface with specified properties.
KEYWORDS: Hydrogen fluoride lasers, Energy efficiency, Pulsed laser operation, Laser energy, Electron beams, Chemical lasers, Switches, Chemical reactions, Diodes, Argon
Non-chain HF lasers initiated by electric discharge and e- beam are described. A generator with an inductive energy storage and semiconducting opening switch was used for discharge formation. The generator was shown to be very promising for development of efficient discharge HF lasers with high output energy. It produces very uniform discharge in SF6-H2(C3H8) gas mixtures at elevated pressure and increases its stability. Discharge HF laser efficiency up to 5.5% was demonstrated. Radially convergent e-beam was used to pump 30 1 HF laser. Optimal gas mixture SF6:H2 equals 8:1 under pressure of 0.45 atm was chosen to provide no more than two-fold specific output power variations across the laser beam area. Output energy as high as 115 J and efficiency with respect to e-beam energy deposited into gas mixture up to 7-8% were demonstrated. Total laser energy and efficiency with respect to deposited energy at pressure of 1.1 atm when the output distribution was non-uniform were found to be up to 200 J and 11%, respectively. The `jump' of pressure in SF6-H2 mixture at the instance of e-beam injection was found to be lower than that in excimer laser mixtures due to SF6 high density. This simplifies creation of wide-aperture e- beam HF-lasers. We expect that the use of pulse generators and wide-aperture laser setup available at HCEI enable us to develop 1 kJ non-chain HF laser initiated either by self- sustained discharge or e-beam.
Design and operating parameters of powerful KrCl((lambda) approximately 222nm), XeCl((lambda) approximately 308nm) excilamps with different discharge geometry pumped by continuous glow discharges along with Ar2((lambda) approximately 126nm) and Kr2((lambda) approximately 146nm) excilamps pumped by barrier discharge are presented. Excilamps with high spatial uniformity of the output and gas lifetime up to 100 hours were developed. It was shown that efficiency of luminescence of exciplex molecules of about 30 percent can be obtained in high-voltage glow discharge and positive column of glow discharge. Output at (lambda) approximately 222nm up to 200 W from single excilamp and 500 W from three excilamps, operated in parallel, was demonstrated.
Results of the experimental study of powerful lasers pumped by a radially convergent electron beam and powerful excilamps are presented. Laser radiation energies of 110, 90, 100, and 50 have been obtained at (lambda) equals 308, 249, 1730 and 2030 nm, respectively. Excilamp average power of 130 W have been obtained at (lambda) approximately 222 and 208 nm, the efficiency was up to 14%.
The results of an experimental study of coaxial exciplex lamps pumped by various types of discharge (the longitudinal discharge, barrier discharge, or continuous glow discharge) are presented. The mixture compositions and pressures as well as the pumping pulse parameters have been optimized for the production of radiation with (lambda) equals 350, 308, 249, 222, and 193 nm. Exciplex lamps with a radiating surface area of 570, 840 and 1300 cm2 have been created. The average radiation power achieved for (lambda) equals 222 nm is up to 4 W and for (lambda) approximately 308 and 350 nm is approximately 10 W. The possibility of an inductive energy store with a semiconductor opening switch being used for pumping a longitudinal-discharge-based exciplex lamp has been demonstrated.
Simple readily manufacturable laser designs pumped by a self-sustained discharge are outlined. The outcomes of tests on laser action from exciplex molecules (ArF*, KrCl*, XeCl*, and XeF*) on electronic transitions in N2, N2+, F2, and F and vibration transitions in CO2 and HF are presented.
Output control of the XeCl- and KrCl-lasers is summarized. Output energy, pulse duration, beam divergence, and linewidth characteristics are investigated. The results of SRS conversion of the XeCl- and KrCl-lasers radiation in hydrogen gas and lead vapor are presented.
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