Effects of density scale length on backward and forward stimulated Raman scattering in 0.53 μm laser–plasma interaction

Abstract

Forward and backward stimulated Raman scattering (SRS) have been investigated in three different plasma geometries: in exponential density profile, in Gaussian density profile, and in quasihomogeneous preformed plasmas. The experiments were performed with the same irradiation setup at 0.53 μm wavelength and at a laser intensity ∼1015 W/cm2. Time-resolved spectra and energy rates of this instability have been measured in the three experiments. A strong increase of the backward SRS energy rate—up to 1%—with the increasing length of the plasma was observed. From data analysis, backward SRS is explained in terms of absolute instability. On the other hand, forward SRS can be interpreted by considering linear scattering of the incident laser light on the plasma wave driven by backward SRS. This assumption is adequately supported both by the spectral characteristics and by the energy rates of the forward emission light.