Theory of stimulated Brillouin scattering in a rarefied inhomogeneous plasma

A theory is developed of stimulated Brillouin scattering (STBS) in a rarefied inhomogeneous plasma with an arbitrary density profile and transparent to the waves involved in the interaction. In contrast to the generally accepted view on the convective nature of STBS, an absolute instability effect has been identified. The instability threshold and growth rate are determined for arbitrary directions of the radiation and arbitrary polarizations of the scattered wave. An investigation is made of STBS arising from distributed heat sources in the bulk of a plasma. It is found that up to the absolute instability threshold the dependence of the scattering intensity on the pump intensity is exponential and corresponds to convective amplification at all resonance points. Beyond the absolute instability threshold the convective instability is suppressed and it corresponds to wave amplification at just one resonance point.