INVESTIGATIONS OF STIMULATED RAMAN SCATTERING FROM HIGH DENSITY UNDERDENSE PLASMAS IRRADIATED BY A 0.35 MICRON LASER.

摘要

Studies of stimulated Raman back and forward scattering and the generation of high energy electrons at 0.35 microns are presented. To isolate the various phenomena occurring at different densities, we attempted to control the plasma density by varying the thickness of the foil targets and also by using foam targets of variable average density. The frequency of the scattered light is used as a diagnostic to measure the plasma density. Time resolved and time integrated spectra for various plasma densities are discussed. Also, the measured energy and angular distribution of the high energy electrons from foil targets are presented. Two-plasmon decay is suggested as the probable mechanism generating the hot electrons.;The backscattered light presents a broadband spectrum in the sub-half-harmonic region. This spectrum is limited by a sharp cut-off near 400 nm and by a spectral gap near the half-harmonic region. The half-harmonic spectrum is shown to be split into a red and a blue shifted peak. Effects of the self-generated magnetic fields and plasma temperature on Raman scattering and two-plasmon decay, respectively, are examined as possible mechanisms responsible for the splitting of the half-harmonic spectrum. Finally, a discussion of the effects of the coupling of Raman and Brillouin scattering on the Raman spectrum is presented with emphasis on the quarter critical region. This last mechanism is suggested to contribute to the splitting of the half-harmonic light.