Optical Discharge Plasma Research Articles

Influence of polarization of radiation on steady-state 180° stimulated Brillouin scattering in gyrotropic media

A theoretical analysis is made of the dependence of the intensity of a Stokes wave on the propagation coordinate in the case of steady-state 180° stimulated Brillouin scattering in an optical discharge plasma when the pump radiation is elliptically polarized.

Diagnostics of an optical discharge plasma sustained in atmospheric air by neodymium laser radiation

Measurements of the temperature distribution and electron density were made in an optical discharge, sustained in atmospheric air by 1.06-μ laser radiation of ~1 MW/cm2 intensity. The plasma temperature within the beam was ~20 kK and the electron density was 2×1017 cm−3. The measured temperature distribution was used to show that about 90% of the energy absorbed by the discharge was carried away by the characteristic plasma radiation, and less than 10% by heat conduction. The method of schlieren photography was used to determine the shape and dimensions of the discharge as a whole, including a region of heated gas surrounding the ionized core. The energy distribution in the various discharge zones was determined.

Optical discharge in air of reduced density containing solid particles

An experimental study was made of the influence of the pressure of air in the range 25–743 Torr on the dynamics of the appearance of an optical discharge plasma initiated on a thin tungsten filament by λ=1.06 laser radiation. A study was made of the transmission by the discharge plasma and of the threshold of its formation in an aerosol medium as a function of the air pressure.

Refraction of laser radiation by an optical discharge plasma

Measurements were made of the radial intensity distributions of a laser beam transmitted by an optical discharge plasma sustained by it. The distributions provided a direct experimental proof of refractive broadening of the focal spot. A quantitative measure is proposed for the degree of refraction by optical discharges in which the energy balance is determined by radiative losses.

Transmission of laser radiation by an optical discharge plasma and the channel discharge model

An experimental investigation was made of the structure of optical discharges in air and in argon in a quasi-cw CO2 laser beam. Measurements of the fraction of the laser power transmitted by the discharge plasma and of the power density at the center of the focal spot, when the plasma was present, showed that the heating of the plasma in the beam propagation zone to temperatures above 17 kK was accompanied by its bleaching in the beam and by a peaking of the beam intensity distribution in the focal plane. A channel model of the optical discharge is proposed to provide an analytical description of its temperature distribution in the laser beam. Sufficient conditions for the discharge bleaching regime are determined.

Structure and properties of an optical breakdown plasma in a CO2laser beam near a target surface

An experimental investigation was made of a surface optical discharge plasma in a CO2 laser beam. The spatial temperature distributions were measured in the optical discharge plasma and on the surface of the irradiated target in the presence of the optical discharge. It was found that the optical discharge in the target vapor was localized in the caustic of the focused beam, while that in the gas surrounding the target moved a considerable distance from the target. This was due to the difference between their energy balance conditions. An optical discharge in the target vapor can increase substantially the power flux absorbed by the target at the center of the focal spot, while one in the gas transfers the power absorbed from the laser beam to an area which is considerably larger than that of the spot. The influence of the laser beam focusing conditions on the efficiency of the localized interaction with the target is indicated and methods are proposed for increasing this efficiency in the presence of plasma.

Superdetonation optical discharge waves in air (λ = 1.06 μ)

An experimental investigation was made of the superdetonation nature of the growth of an optical discharge plasma on thin tungsten filaments. The maximum recorded velocity of the ionization front growing on a filament 45 μ in diameter was 500 km/sec and the intensity of the emitted radiation was ~ 1010 W/cm2. The velocity of the ionization front was inversely proportional to the filament diameter.

Two gasdynamic propagation regimes of a subsonic optical discharge

A method was developed for recording the motion of gas in the region of an optical discharge which is based on observing the transport of specially created optical inhomogeneities by the gas. It was used to confirm the existence of a cold gas ahead of the discharge front and to obtain quantitative data concerning its motion. The conditions were realized for the propagation of an optical discharge plasma completely immersed in a laser beam, the laser radiation being only weakly absorbed in the discharge. A sudden change in the discharge front velocity on reaching the lateral surface of the laser beam indicated that the gasdynamic regime of the propagation of the slow combustion optical discharge had changed.