Stimulated Brillouin scattering in an inhomogeneous plasma with broad-bandwidth thermal noise

Abstract

Stimulated Brillouin scattering in a plasma containing broad‐bandwidth thermal noise was considered. Plasma profiles which are inhomogeneous (for example, because of a velocity gradient) were studied. At each point in the profile, a different electromagnetic wave can be resonant with the pump wave and a local ion acoustic wave, and can thus be amplified from its noise level. Some difficult points of the linear theory of this process are first examined. Then a nonlinear equation is derived, which governs the decrease of the incident‐wave amplitude as it propagates toward the critical density surface. Solutions of this equation predict a maximum value of the absorbed intensity, I_max. For incident laser intensities I_in, higher than this value, only a fraction I_max/I_in is absorbed.