The paper studies the dynamics of a nanosecond diffuse discharge with no additional preionization at a voltage rise time of less than 1 ns and its effect on drinking and distilled water. It is shown that the diffuse discharge is formed due to avalanche charge multiplication initiated by fast electrons and is sustained by secondary breakdown waves through ionized gas channels. Fourier transform infrared spectroscopy reveals that repeated exposure to the discharge changes the absorption spectra of drinking and distilled water such that the stretching vibration band of OH groups broadens and lacks clearly defined peaks. The water conductivity after irradiation increases. Probably, this is due to cluster rearrangement of water molecules.
A high-pressure CO2 laser with a discharge initiated by a subnanosecond electron beam formed in the laser operating medium under pressure 5 atm. Radiation energy of 40 mJ in active volume of ~ 4 cm3 at radiation duration of 20 ns has been obtained. Laser operation at pulse repetition rate (p.r.r.) of up to 5 Hz has been demonstrated. Specific energy input of ~0,07 J/cm3.atm have been realized in laser operating gas mixture CO2:N2:He = 1:1:6 under pressure of 5 atm on the course of a pulsed non-sustained discharge with pre-ionization.
The studies of luminescence of synthetic ruby, natural spodumene and natural IIa type diamond under the action of laser radiation at 222 nm and subnanosecond avalanche electron beam (SAEB) were carried out. It was demonstrated that SAEB parameters allow obtaining high-intensity luminescence of various crystals in the normal conditions without any vacuum equipment used. At the both types of excitation, ruby emission spectra were similar demonstrating luminescence of chrome only. It was shown that photoluminescence spectra of the spodumene and diamond samples contained some bands being absent in SAEB-initiated cathodoluminescence spectra.
Formation of nanosecond discharges in air under atmospheric pressure at different voltage pulse polarities and various discharge gap geometry has been investigated. It has been shown that in a wide range of experimental conditions at high voltage nanosecond pulses used, electrode construction or voltage pulse polarity have no essential effect on volume character of a discharge. With negative voltage pulses applied to a potential electrode, no matter what construction it has, X-ray radiation is being recorded both from anode surface and volume. Under a voltage pulse of positive polarity, X-ray radiation is recorded with the lower intensity. It has been shown that with subnanosecond voltage pulse rise time and a discharge of diffusion character, X-ray radiation is observed fiom a brightly glowing corona discharge area. The mean energies and velocities of fast electrons in nitrogen have been calculated. It was shown that head-on collisions establish the fact that the mean velocity of a group of fast electrons is permanent. These head-on collisions of electrons lead to emission of X-ray radiation from a volume.
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).
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.
The experimental results of the studies on process of radiation interaction of the pulsed CO2 - laser with polytetrafluoroethylene (PTFE) are presented. A dependence of PTFE transmission factor at λ = 10.6 μm versus temperature in the range -90 - 300°C has been obtained.
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.
It has been shown that the use of gas diodes with cathode electric field enhancement and voltage pulses having a short leading edge allow to form high-current subnanosecond electron beams. An electron beam appears at voltage pulse leading edge with duration at FWHM not more than 0.3 ns. On the beam current termination the discharge is usually continued in a quasi-stationary mode having a volume character. With a diode filled in with air under atmospheric pressure, beam current amplitude over ~240 A at a pulse duration at FWHM of ~0.2 ns and current density of ~40 A/cm2 was obtained. It has been also shown that at a small gas diode inductance the subnanosecond electron beams are formed in various gases in a wide pressure range (up to 6 atm in helium, and up to 4 atm in nitrogen). It has been established that with the new method an electron beam is formed due to critical field reached between an anode and plasma propagating from a cathode.
Atmosphere pressure CO2-laser with e-beam initiated disch arge formed in laser operating mixture has been created. Energy of radiation as 18 mJ in active volume of ~6 cm3 has been obtained. Laser operation at pulse repetition rate of up to 5 Hz was demonstrated. Specific energy input as ~0.1 J/cm3 was realized in gas mixture CO2:N2:He = 1:1:4 under atmosphere pressure in the process of a pulsed non-self-sustained discharge with ionized amplification. This method of discharge initiation is rather promising for creation of short-pulse high-pressure lasers.
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.
Experimental results obtained on the pulsed repetitive CO2 laser pumped by a longitudinal discharge are reported. The laser pumping system included both the inductive energy storage with semiconductor opening switch and capacitive energy storage. The average radiation power of 300 mW was reached at the pulsed repetitive rate of 10 Hz. The duration of radiation pulse at FWHM was 60 μs, and the intrinsic efficiency was 5,5%. It has been shown that the radiation energy in a pulse at this parallel-flat cavity laser is sufficient for glass marking.
The formation of a beam of runaway electrons in a diode filled with helium at a pressure from 0.1 to 760 Torr was studied under conditions of a pulsed (4 ns) high (200 kV) voltage applied to the discharge gap. The experimental data results indicate that the electron beam is generated either at a large strength of electric field, when the fraction of runaway electrons is large, or in the field of low strength, where intensive electron multiplication takes place. In the latter case, cathode plasma propagates to anode at high velocity, at that with electrical field distribution in gas diode area the critical value of E/p is reached either due to geometric quotient leading to formation of nanosecond and subnanosecond electron beams. The electron beams obtained in the helium-filled diode had the current amplitude of up to 200 A (corresponding to the current density above 20 A/cm2) at electron energy of ~130 keV.
Properties of plasma produced in volume nanosecond high-pressure discharge and its formation conditions under elevated pressure in air, nitrogen, krypton, argon, neon and gas mixtures Ar-N2, Ar-Xe, CO2-N2-He in the gap with the cathode having small curvature radius have been investigated. Time-amplitude characteristics and radiation spectra of plasma in different gases in the range of 230-600 nm were defined. Lasing in the gas mixture Ar-Xe at active length of 1.5 cm has been achieved by excitation through volume nanosecond high-pressure discharge. Comparison of spectral radiation in nitrogen, krypton, argon, and neon under pumping of mentioned gases by volume discharge in non-uniform electric field, by nanosecond e-beam, and by volume pulsed discharge in the uniform electric field with high initial voltage was made. Lasing has also been obtained in the gas mixture CO2-N2-He under pumping by e-beam initiated discharge. The electron beam was formed in a gas diode filled the same gas mixture.
This paper reports on experimental study of subnanosecond e-beam formed in air under atmospheric pressure. An electron beam with amplitude of ~ 170 A with duration at FWHM ~0.3 ns has been obtained. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is cathode type and plasma protrusions occurred on the cathode. It is shown that in order to get maximum e-beam in gas diode, the discharge in gas diode should be volume.
Subnanosecond electron beams with the record current amplitude (~70 A in air and ~200 A in helium) were produced at the atmospheric pressure. The optimal generator open-circuit voltage was found for which the electron-beam current amplitude produced in a gas diode was maximal behind a foil. It was established that electron beam was produced at the stage when the cathode plasma closely approaches anode. It was shown that a high-current beam can be produced at high pressures because of the presence of the upper branches in the curves characterizing the electron-escape (runaway) criterion and the discharge-ignition criterion (Paschen curve).
Investigation of the modes of thin metal and ceramic films (0,3-1 μm) removal from the glass and stainless steel substrate by IR and UV laser radiation has been performed. It is presented that the efficient film destruction and removal occurs due to laser induced thermal strength under laser fluxes of ~0.5 J/cm2 not sufficient for phase transformation.
Formation of microscopic size colored dots on titanium foil surface by pulsed IR-laser irradiation was studied. It was found that the dot on titanium surface changes its color from yellow to blue as the exposure is increased. According to our numerical calculation, the colored dot formation is accompanying with titanium surface melting and partial evaporation. At pulse-periodical irradiation mode it can result in foil break-through.
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.
The interaction of pulsed periodical CO2-(λ~10.6 µm), and Xe-(λ~1.73 μm) lasers radiation with surfaces of polymers has been studied. Correlation between parameters of surface erosion (area of crater and amount of evaporated material versus laser focus position and number of pulses) was investigated using teflon (polytetrafluoroethylene-PTFE) and vinypros (plasticized semi-transparent polyvinylchloride) sample. Monitoring of erosion track on surfaces was performed through optical microscopy. It has been shown that at pulsed periodical CO2-radiation interaction with teflon and vinypros the sputtering of polymers with formation of submicron-size particles occurs. Dependencies of particle sizes, form and sputtering velocity on laser pulse duration and target temperature have been obtained.
The interaction of Xe- (λ~1.73 µm) and XeCl- (0.308 μm) lasers radiation with surfaces of metal and TiN-ceramic coatings on glass and steel substrates has been studied. Correlation between parameters of surface erosion (area of crater and amount of evaporated material versus laser focus position and number of pulses) was investigated. Monitoring of laser induced erosion on smooth polished surfaces was performed using optical microscopy. The correlation has been revealed between characteristic zones of thin coatings damaged by irradiation and energy distribution over laser beam cross section allowing evaluation of defects and adhesion of coatings.
Presently, from the world data available on interaction of laser radiation with metal and dielectric surfaces and development of experimental diagnostic techniques by itself it is possible to raise a reverse question, namely, restoration of laser radiation energy spatial distribution through surface imprint. With this in mind, we have made the detailed morphology of imprint of a pulse HF-laser interaction with carbon steel surface through atomic force microscope. Interaction of the radiation of a relatively short pulse of ArXe-laser ((tau) ½equals400 ns, (lambda) equals1,73 micrometers , Q ~ 20 J/cm+2)) with carbon steel surface of 40X (4140 (USA)) type besides the surface layer hardening leaded to decrease of steel hardness at below original value on depth of about 10 - 12 micrometers . This effect can be related to occurrence of deformation and thermal residual stresses in the subsurface layer. At multiple-pulse interaction (~500 pulses) of UV-laser focused radiation ((lambda) equals0,222 or 0,308 micrometers , (tau) ½equals 12 or 20 ns) with the steel 40X (4140 (USA)) surface a distinct interference imprint of laser beam is formed after diffraction at outer diaphragm being determined by its form.
The complex of experimental installations for studying of laser radiation interaction with surface of metals has been established. At titanium surface irradiating depending on the accumulated laser radiation energy, the surface color might be changed from bright yellow to red and deep-blue colors. The presented results testify to the possibility to use the change of titanium surface color at heating by laser irradiation in the open air to obtain dot raster images. Presently, form the world data available on interaction of laser radiation with metal and dielectric surfaces and development of experimental diagnostics techniques by itself it is allowed to raise a reverse question, i.e., restoration of laser radiation energy spatial distribution through surface imprint. Using imprints, it is also possible to make an express diagnostics of multi-layer surface coatings. With this in mind, we have made the detailed morphology of imprint of the pulsed HF-laser interaction with carbon steel surface through atomic force microscope.
Energy, temporal and spectral characteristics of HF-laser pumped by non-chain chemical reaction initiated by radially converging e-beam, planar e-beam and non-self-sustained discharge have been investigated. The major channels of vibrationally excited HF molecules formation have been analysed. It has been confirmed that the high efficiency (~ 10 %) of non-chain HF laser can be reached only by simultaneous atomic and molecular fluorine formation under the action of e-beam and molecular fluorine participation in the inversion releasing process. It is shown that the laser pulse has a complex spectral-temporal structure caused by consecutive generation of the P-lines P2?P1?P3?P4?P5?P6 and overlapping of the rotary lines of the same oscillatory band and separate oscillatory lines during a pulse of radiation. With e-beam pumping of a 30 1 active volume laser, the output energy as high as 115 J and efficiency with respect to e-beam energy deposited into gas mixture up to 8 % were demonstrated. The optimal gas mixture SF6 : H2 =8 : 1 under pressure of 0.45 atm has been obtained. At pressure 1 .1 atm and non-uniform output distribution, total laser energy and efficiency with respect to e-beam energy deposited into gas were found to be up to 200 J and 1 1 %, respectively. Use of e-beam initiated low pressure pulsed discharge for excitation HF molecules leads to increase of radiation energy in 2.8 times. Also investigations on zeolite-based different absorbents influence on energy stability of HF-laser are presented and radiation energy decay after 103 shoots not more than 15-20 % is gained.
Energy, temporal and spectral characteristics of HF-laser pumped by non-chain chemical reaction initiated by radially converging e-beam, planar e-beam and non-self-sustained discharge have been investigated. The major channels of vibrationally excited HF molecules formation have been analyzed. It has been confirmed that the high efficiency of non-chain HF laser can be reached only by simultaneous atomic and molecular fluorine formation under the action of e-beam and molecular fluorine participation in the inversion releasing process. It is shown that the laser pulse has a complex spectral-temporal structure caused by consecutive generation of the P-lines and overlapping of the rotary lines of the same oscillatory band and separate oscillatory lines during a pulse of radiation. With e-beam pumping of a 30 1 active volume laser, the output energy as high as 115 J and efficiency with respect to e-beam energy deposited into gas mixture up to 8 percent were demonstrated. The optimal gas mixture SF6: H2 equals 8:1 under pressure of 0.45 atm has been obtained. At pressure 1.1 atm and non-uniform output distribution, total laser energy and efficiency with respect to e-beam energy deposited into gas were found to be up to 200 J and 11 percent respectively. E-beam initiated low pressure pulsed discharge for excitation HF molecules leads to increase of radiation energy in 2.8 times.
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.
Basic principles of weak echo-signals laser receiving are briefly summarized and autodyne lidars employing this way of weak signal detection while sounding the atmosphere are described. Detection of weak light signals by a hybrid laser is studied theoretically and experimentally. Autodyne lidar modifications, namely the multipurpose cw parametric autodyne lidar which allows one to increase a set of retrieved from the received by the laser echo-signal optical and dynamic characteristics of an atmospheric path and a remote retroreflector and a hybrid lidar in which positives of conventional cw autodyne lidars are combined with those inherent to pulsed lidars are discussed
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.
The peculiarities of output radiation formation in electroionization CO2-lasers with smooth tuning of frequency are experimentally investigated. The possibility of the output radiation formation using system master oscillator-amplifier in one excited volume is considered. Operation of tuned CO2-laser in pulse-repetitive mode is tested.
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.
This paper presents investigations of the carbon-dioxide lasers excited using two techniques: e-beam controlled discharge and e-beam ignited discharge. The working mixtures were CO2-N2-He, CO2-N2 and CO2-N2He- H2. We can change working mixture composition, its pressures, pumping power and the laser pulse duration from 50 ns to 10 microseconds. The operating time of a repetitive carbon-dioxide lasers excited by e-beam controlled discharge or e-beam ignited discharge in nonstop mode is determined by the lifetime of the foil separating the vacuum gap from the gas cell. The radiation energy of 3 kJ has been achieved in the active volume of 50 1 at pressure of 2 atm. When 12 1 active volume was used the energy deposited in to the CO2:N2:He equals 1:2:2 mixture was as high as 0.6 kJ/lXatm while the radiation energy was about order of magnitude 80 J/lXatm.
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