Yu. I. Bychkov

EFFICIENT HIGH-HOMOGENEOUS WIDE-APERTURE EXCIMER DISCHARGE USING A STABILIZING LOW-CURRENT PREDISCHARGE

A technique of initiation of a self‐sustained electrical discharge for pumping excimer lasers, based on the use of a stabilizing predischarge with an electron density Ne∼1012–1013 cm−3, has been developed. It has been demonstrated that such an auxiliary discharge is stable for random disturbances of the plasma parameters. An efficient, stable, and highly homogeneous pumping discharge of duration up to 800 ns with an aperture of 6×12 cm2 and current density of ∼300 A/cm2 has been realized in Ne(He,Ar)/Xe(Kr)/HCl mixtures. The proposed technique can be used in developing wide‐aperture excimer lasers and shows promise for creating high‐repetition‐rate systems of kilowatt average power.

A 10‐J electric‐discharge‐pumped phototriggered XeCl laser

An electric‐discharge‐pumped XeCl laser using phototriggering by x rays is reported. 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 ∼3‐l active volume with an efficiency ≳2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A stability analysis of the discharge pumping has been made for the XeCl laser in terms of the current‐voltage characteristic model. The method for parametric optimization of such systems is described.

Two-dimensional simulation of initiation and evolution of a plasma channel in the XeCl laser pumping discharge

We present two-dimensional simulation results of the formation and evolution of a diffuse plasma channel in the XeCl pumping discharge. Channel formation was initiated by metallic convexity at the cathode surface with a characteristic dimension of ∼0.1 cm. Two pumping regimes were considered. Initial voltage in the second regime was increased 1.6 times and impedance was decreased 2 times in contrast with the first regime. Evolutions and spatial distributions are presented for electron density, electric field, and frequencies of the main process. In the first regime, the diffuse plasma channel forms. The main processes causing development of the plasma channel are inhomogeneous distribution of the electric field, increase of the stepwise ionization frequency at n e ∼ 10 15 cm −3 , and depletion of HCl. Increasing of the initial voltage and decreasing of the impedance in the second regime results in a quick rise of the discharge current and electron density in the discharge gap, and uniform discharge takes place during the current pulse.

Rapid increase in the delay time for the breakdown of gas-filled gaps in high electric fields

An experimental study is reported of the delay-time statistics for electrical breakdown in air in intense electric fields E = 100–200 kV/cm. The dependence of the statistical delay time tst for the breakdown on the gap width δ is obtained for various fields E. With E = 100 kV/cm and with an air pressure of p = 1 atm, the delay time is ∼20 nsec and depends weakly on δ in the range δ5 = 3–10 mm. As the gap width is reduced from 3 to 2 mm, tst increases sharply, reaching 3000 nsec. The gap width at which the sharp increase in tst sets in decreases with increasing E. The gap-width dependence of tst has the same nature at different pressures. The minimum delay time has been measured to be ∼8 nsec.

Wide-aperture CO2 lasers pumped with an electron-beam-controlled discharge

This review paper presents the results obtained during the development and study of three high-power wide-aperture CO2 lasers (λ=10.6 μm) pumped with a discharge controlled by an electron beam. In developing these lasers, the method of formation of a space discharge at elevated pressures due to uniform ionization of the working mixture by an electron beam with an energy of some hundreds of kiloelectron-volts was used, which was proposed by researchers at the Instute of High-Current Electronics (IHCE).

Two-dimensional simulation of the development of an inhomogeneous volume discharge in a Ne/Xe/HCl gas mixture

The kinetic processes accompanying plasma column formation in an inhomogeneous discharge in a Ne/Xe/HCl gas mixture at a pressure of 4 atm were investigated by using a two-dimensional model. Two cathode spots spaced by 0.7 cm were initiated by distorting the cathode surface at local points, which resulted in an increase in the field strength in the cathode region. Three regimes differing in the charging voltage, electric circuit inductance, and electric field strength at the local cathode points were considered. The spatiotemporal distributions of the discharge current; the electron density; and the densities of excited xenon atoms, HCl(v = 0) molecules in the ground state, and HCl(v > 0) molecules in vibrational levels were calculated. The development of the discharge with increasing the electron density from 104 to 1016 cm−3 was analyzed, and three characteristic stages in the evolution of the current distribution were demonstrated. The width of the plasma column was found to depend on the energy deposited in the discharge. The width of the plasma column was found to decrease in inverse proportion to the deposited energy due to spatiotemporal variations in the rates of electron production and loss. The calculated dependences of the cross-sectional area of the plasma column on the energy deposited in the discharge agree with the experimental results.

Research of short pulse discharge XeCl laser

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.

Increase in the laser pulse length of lasers operating on self-quenching transitions

The reasons limiting the time for maintaining population inversion in lasers operating on self-quenching transitions are investigated theoretically and experimentally. It is shown how the nature of the pumping of the upper laser level affects this property of the active medium in N2 and N2-Ar lasers.

Development of an electrical discharge in strongly overstressed gaps with a low air pressure

The time of switching, “step” length and delay time of a discharge were investigated in this present project, under the following experimental conditions: plain brass electrodes, two- to 20-fold overvoltage and air pressure 30 mm Hg. In addition, the relative intensity of bremsstrahlung from the anode was measured and theγ-quanta energy was determined by the radiation attenuation method in aluminum plates. It is suggested that such short delay times obtained can be explained first of all by the accelerated motion of electrons and secondly by the bremsstrahlung from the anode.

Electron-optics study of the development of an electric discharge in a gas at high-electric field intensities and with one-electron ignition

A study was made of the luminous region in a discharge gap with copper electrodes, a field of E = 80 kV/cm, air at atmospheric pressure, and a gap width of 4 or 2 mm. The cathode was irradiated with a spark to ignite the initial electrons. The electron current from the cathode was 0.2 · 109 electrons/sec. The exposure time per frame was 3 · 10−9 sec. With a gap width of δ = 4 mm, a luminous region is observed at the cathode 2 nsec after voltage is applied to the gap; this region propagates toward the anode, simultaneously increasing in diameter, at a velocity of ∼ 103 cm/sec. A voltage drop is established across the gap approximately 0.5 nsec after the luminous front arrives at the cathode. In narrower gaps, the voltage drop is established across the gap a considerable time after the luminous region has crossed the gap.