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A high-pressure CO{sub 2} laser with a discharge initiated by an electron beam of sub-nanosecond duration in the laser gas mixture at a pressure up to 5 atm is fabricated. For the 20-ns pulses the energy from the active volume {approx} 4 cm{sup 3} amounted to 40 mJ. The laser operation at a pulse repetition rate up to 5 Hz is demonstrated. In the gas mixture CO{sub 2}:N{sub 2}:He = 1:1:6 at a pressure 5 atm, the specific energy deposition of {approx} 0.07 J cm{sup -3} atm{sup -1} is obtained in the process of a non-self-sustained discharge with ionisation amplification.

Luminescence of crystals of natural spodumene and natural diamond of the type IIa is studied upon excitation by a laser at a wavelength of 222 nm and by a subnanosecond avalanche electron beam (SAEB) formed in air at the atmospheric pressure. The photoluminescence spectra of spodumene and diamond are shown to exhibit additional bands, which are absent upon SAEB excitation. It is demonstrated that SAEB excitation allows one to analyse various crystals under normal conditions without using any vacuum equipment.

The phenomenon of electric breakdown in air at atmospheric pressure without additional preionization was studied by experimental and theoretical methods. Using voltage pulses of different polarity with subnanosecond leading front and nanosecond width, volume discharge can be obtained under such conditions between electrodes of various configurations, in particular, between two point electrodes. The development of an ionization wave in nitrogen is described within the framework of a diffusion-drift approximation in a spherical geometry. The fact that the qualitative character of discharge is independent of the voltage pulse polarity is explained by the multiplication of background electrons in the high-density gas.

It is shown that a volume discharge is formed in a nonuniform electric field for the short leading edge of a voltage pulse and nanosecond pulse duration without any additional preionisation source in various gases at pressures higher than atmospheric (6 atm in helium and 3 atm in nitrogen). Lasing at atomic transitions in Xe is obtained in an Ar—Xe mixture under a pressure of 1.2 atm for an active length of 1.5 cm. A record-high specific power input (more than 0.8 GW cm-3 under a pressure 1 atm in air) is realised in the volume discharge stage. The volume discharge is formed due to preionisation of the discharge gap by fast electrons accelerated due to amplification of the electric field in the cathode region and in the gap. In a nonuniform electric field, volume discharge is realised under a quasistationary voltage from 10 to 180 kV across the gap, at a pulse repetition rate of up to 160 Hz and for various discharge gap geometries.

Lasers on the second positive nitrogen system (the C3Πu—B3Πg electronic band, λ=337.1 and 357.7 nm) are studied. Mixtures of nitrogen with electronegative gases (SF6 and NF3) are pumped by transverse and longitudinal discharges. The amplitude—time and spectral characteristics of a laser pumped from capacitive and inductive energy storage units are measured. The output energies of the laser pumped by a transverse discharge from a capacitive and inductive storage units are 17 and 18.4 mJ, respectively. It is shown that the mean output energy in N2—NF3 mixtures continues to increase at higher pulse repetition rates than in nitrogen. Under the pumping by a transverse discharge, two-peak 357.7-nm lasing with a total pulse duration of >40 ns is achieved. It is established that adding SF6 to the mixture enhances the output power of a longitudinal-discharge-pumped nitrogen laser.

The effect of IR and UV laser pulses on thin metal and composite films on glass substrates as a function of the energy density is studied. Upon irradiation by ~300-ns laser pulses with a nonuniform energy-density distribution over the laser-beam cross section, the characteristic regions can be distinguished on the film surface. The dimensions of these regions correlate with the energy distribution in the beam and correspond to the evaporation, melting, and damage conditions caused by thermal stresses. For a uniform energy-density distribution over the laser-beam cross section and a pulse duration of ~20 ns, the adhesion of metal and composite films to glass was disturbed due to induced thermal stresses without substrate melting. The threshold laser-energy densities required for disturbing the adhesion of titanium, titanium nitride, zirconium, niobium, and stainless-steel films on glass substrates are measured. Numerical estimates of the surface temperature and thermal stresses caused by heating show that the film adhesion to a substrate can be overcome by expending a small fraction of the energy, while most of the energy of thermal stresses goes to the formation of cracks and the kinetic energy of escaping film fragments. It is suggested to use pulsed laser radiation to roughly estimate the adhesion of metal and composite films to glass substrates.

This article reports on experimental studies of subnanosecond electron beams formed in air under atmospheric pressure. An electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼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 the cathode type and occurrence on the cathode of plasma protrusions. It is shown that to get maximum amplitude of the electron beam in the gas diode, the discharge in the gas diode should be volumetric.

Experiments are performed on the formation of coloured dots of a submillimetre size on the titanium foil surface irradiated by pulsed IR lasers. It is shown that the parameters of laser pulses can be selected so that the dots produced on the titanium foil surface will change their colour from yellow to blue with increasing exposure time. The threshold laser power densities required for the formation of contrast coloured dots on the titanium foil surface irradiated by laser pulses with low repetition rates are estimated as ~1.5 × 103 J cm-2 for a 1.73-μm Xe laser and ~2.3 × 103 J cm-2 for a 10.6-μm CO2 laser.

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. Both theoretical results and experimental data indicate that the electron beam is generated both at a large strength of the electric field, when the fraction of runaway electrons is large, and in a field of low strength, where intensive electron multiplication takes place. In the latter case, a high current can be obtained despite a small fraction of runaway electrons relative to their total number. The electron beams obtained in the helium-filled diode had a current amplitude of up to 140 A (corresponding to a current density above 10 A/cm2) at an electron energy of ∼150 keV.

Subnanosecond electron beams with the record current amplitude (∼70 A in air and ∼200 A in helium) were produced at 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 the electron beam was produced at the stage when the cathode plasma closely approaches the 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).

The amplitude — time and spectral characteristics of laser radiation and discharge characteristics in mixtures of SF6 with hydrogen and hydrocarbons at a high lasing efficiency are investigated. Lasing efficiencies of ~10 % with respect to the deposited energy are obtained under the pumping from capacitive and inductive energy storage units. It is shown that, during a pump pulse, the maximum efficiencies are achieved at high values of the parameter E/p in the laser gap. When profiled electrodes and UV preionisation are used, a specific output energy of a nonchain HF laser of ~140 J L-1 atm-1 and a lasing efficiency of ~4.5 % with respect to the stored energy were obtained. It is shown that the emission spectrum of a nonchain HF laser operating at high lasing efficiencies becomes significantly wider and cascade lasing is realised on the ν(3–2) → ν(2–1) → ν(1–0) vibrational transitions at several rotational lines.

Experimental and theoretical investigations were made of the excitation and emission from a high-power HF laser pumped by a nonchain chemical reaction initiated by a radially converging electron beam. The distribution of the specific radiation energy in the output beam was determined and the distribution of the input energy over the laser chamber cross section was calculated for various gas mixtures. The space-charge field influenced the input energy distribution. The output radiation energy of a mixture of the SF6 : H2=8 : 1 composition was ~115 J at a pressure of 0.45bar when the active volume was ~30 litres, the efficiency relative to the input energy was ~7%—8%, and the distribution of the radiation energy over the output beam cross section was relatively uniform. For the same input energy, because of the high density of SF6, a pressure jump in SF6— H2(D2) mixtures resulting from the combined effect of the electron beam injection and the chemical reaction was several times less than in active mixtures of exciplex lasers.

Subnanosecond electron beams can be formed in gas-filled diodes at high pressures (up to 6 and 4 bar in helium and nitrogen, respectively). In a diode filled with air at atmospheric pressure, a beam current amplitude above 240 A was obtained at a pulse duration (FWHM) of ∼0.2 s and a beam current density of ∼40 A/cm2.

An atmospheric-pressure CO2 laser with an electron-beam-initiated discharge produced in a working mixture is developed. The laser output energy of 18 mJ from a ~6-cm3 active volume is achieved. The laser operation with a pulse repetition rate of up to 5 Hz is demonstrated. The specific energy deposit of ~0.1 J cm-3 is obtained in the CO2:N2:He = 1:1:4 gas mixture at the atmospheric pressure during a pulsed nonself-sustained discharge with ionisation amplification.

We have studied the conditions for the formation of a pulsed beam of runaway electrons in a diode filled with air at atmospheric pressure, whereby the current and voltage pulses in the system were measured with a subnanosecond time resolution. It is experimentally demonstrated for the first time that the electron beam appears on the leading front of the voltage pulse at a relatively small voltage on the discharge gap. At atmospheric pressure, a full width at half maximum of the current pulse does not exceed 0.3 ns.

We have studied the electron beam formation in a diode filled with a molecular gas at atmospheric pressure. A beam current amplitude of up to ∼20 A at an electron energy of ∼70 keV was obtained in an air-filled diode. It is suggested that the main fraction of runaway electrons at low initial values of the parameter E/p (∼0.1 kV/(cm Torr)) is formed in the space between cathode plasma and anode. As the plasma spreads from cathode to anode, the electric field strength between the plasma front and anode increases and the E/p value reaches a critical level.

The generation and discharge are studied in a nonchain HF laser operating on mixtures of SF6 with hydrogen and hydrocarbons. The specific output energy of the laser is 8.8 J L-1 (73 J L-1 atm-1) and the total lasing efficiency is 5.5%. It is shown that the formation and maintaining of a volume discharge in self-sustained-discharge-pumped HF lasers with a large content of electronegative gases is caused by the accumulation of the volume discharge of negative ions in conducting regions.

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.

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).

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/cm 2 was obtained. It has been also shown that at a smal l 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. Key words: e-beam, running electrons, gas diode, volume discharge

The experimental results of the studies on process of radiation interaction of the pulsed CO 2 - 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.

The subject of study is ultrashort avalanche-produced electron pulses generated in air under atmospheric pressure. The current amplitude of the pulses behind 45-μm-thick AlBe foil exceeds 100 A, and their FWHM is ≈0.2 ns. The conditions of generation of ultrashort pulses persist at repetition rates as high as 1.5 kHz. A volume discharge initiated in an open coaxial-electrode gas diode by high-voltage nanosecond pulses generates hard (> 60 keV) radiation.

A study was made of the excitation of the working medium of a CO2-laser at a pressure of up to 8 atm by an electron beam of duration 15 · 10−9 sec. Results are given of the energy dissipation in a CO2:N2-1∶3 gas medium in the whole range of pressures with E0/p = (18–38) V /cm · mm Hg. The dependences of the time of appearance of the stimulated radiation with respect to the current pulse are given.

An interrupted discharge has been used to examine the production of light in the breakdown of an overvoltage gas gap in air under conditions of E/p = 90–110 V/cm-mm Hg. It is found that there are two types of discharge, the type being dependent on the number of initial electrons: diffuse when there are many electrons and of channel type when there is a single initiating electron. The observed voltage-fall curves for the first type of discharge agree well with theoretical ones derived from the avalanche theory. A study has been made of the dependence of the delay time and switching time on the relative intensity of the illumination used to produce the initial electrons.

The repetitively pulsed regime of an atomic xenon transition laser pumped by an electron beam with various pulse durations and an electron-beam-initiated discharge is studied experimentally. An average radiation power of 2.5 W has been achieved in a quasi-stationary regime for a pulse repetition rate of 5 Hz in a laser pumped by a radially convergent electron beam of duration 100 μs without circulation of the Ar — Xe working mixture. The average output power for a laser pumped by a planar electron beam in quasi-stationary regime is 2 W. It is shown that for a specific energy contribution not exceeding 50 J L-1 and laser excitation by a train of electron-beam pulses at a repetition rate of 50 Hz, the amplitude and duration of the second lasing pulse virtually coincide with those of the first. For a laser pumped by a discharge initiated by a nanosecond electron beam, an average lasing power of 380 mW is achieved under steady-state conditions upon transverse circulation of the working mixture and a pump pulse repetition rate of 25 Hz. Pumping by an electron beam from two accelerators with a pulse duration of a few tens of microseconds under an Ar — Xe mixture pressure of about 1 atm and a specific pump power of 1 — 3 kW cm-3 per pulse is proposed for the development of 1.73-μm repetitively pulsed Xe lasers with a high average output power.

Theoretical estimates are obtained of the threshold energy of a high-pressure pulsed CO2 laser on the assumption that the stimulated emission is due to a single rotational line of the P branch of the 0001-1000 band. These estimates are obtained as a function of the parameters of the resonator and of the CO2 + N2 + He working gas mixture. It is reported that the calculations are in satisfactory agreement with the results of experiments carried out on an electric-ionization CO2 laser at pressures p up to 4 atm. The measured threshold values of the ratio E/p are also reported and it is shown that the presence of helium affects this ratio.