Double stimulated Raman scattering in a plasma

An analysis is made of the simultaneous stimulated scattering of the incident and reflected components of a pump wave by electron density perturbations in a plasma. It is shown that this double stimulated Raman scattering (DSTRS) effect results in an absolute instability of the scattered component. A model of a homogeneous plasma layer of finite thickness is used to find the DSTRS reflection coefficient allowing both for the pump wave depletion and for the plasma wave nonlinearity. It is shown that the DSTRS effect is retained also in a plasma with an inhomogeneous density distribution. In this case the width of the wave interaction region is governed either by electron collisions or by convective transport of plasma waves. The angular and spectral characteristics of DSTRS in an inhomogeneous plasma are considered.