Optical ray retracing of Brillouin backscatter from a nonisothermal plasma

The optical ray retracing of stimulated Brillouin backscatter from a laser fusion plasma has been studied, including the effects of density gradient and flow velocity and allowing the acoustic wave to be weakly damped. The pump is comprised of two plane uniform beams propagating at some angle with respect to each other, producing an interference pattern that behaves as an active grating for the scattered radiation. When the convective loss due to plasma inhomogeneity is small, Bragg diffraction of the scattered radiation results in the reproduction of the same transverse spatial structure as the pump, i.e., the two beams are retraced. However, when the convective loss dominates, the Bragg diffraction is severely affected and the scattered radiation no longer reproduces both beams of the pump with equal intensities or in the correct backward directions.