Nonstationary Stimulated Brillouin Backscattering in Inhomogeneous Density Profiles

Abstract

In inhomogeneous density profiles electromagnetic light is partially absorbed and reflected at the critical surface. In those profiles where the reflection is non-negligible the counterpropagating electromagnetic waves cause standing ion density fluctuations which act as a source for backscattering. To study this effect a simplified model based on the usual three wave interaction as well as an extended model using the nonlinear hydrodynamic description of the ion fluid have been investigated. In certain parameter regions at which absorption and reflection at the critical surface are of comparable magnitude no steady state in the evolution of the back-scattered light can establish over long time intervals. The spectral composition of the backscattering signal shows a strong competition between the frequency shifted stimulated scattering (SBS) and the unshifted reflection process.