Experimental studies of Raman scattering from foam targets using a 0.35 μm laser beam

Abstract

Experimental studies of the forward scattered spectrum and stimulated Raman backscattering from foam targets are presented. An attempt has been made to isolate the effects of the presence of the quarter critical density on the Raman spectrum by creating plasmas with various peak plasma densities. The plasmas created had a length larger than 600 μm and a variable peak density between 0.11nc and slightly higher than 0.25nc. The total Raman reflectivity in the backward direction is of 0.3%, with 80% of its energy being scattered in a range of frequencies between 470 nm and 500 nm for all the targets used. The scattered intensity near the half-harmonic region shows a weak dependence on the presence of the nc/4 density layer. The forward scattered spectrum obtained from targets with average densities between 0.11nc and 0.22nc shows a broadband of frequencies similar to the backscattered spectrum indicating that the forward spectrum is probably being seeded by the beating of the plasma wave from stimulated Raman backscattering (SRS-B) with the ion acoustic wave from stimulated Brillouin scattering (SBS).