The Coupling of Stimulated Raman and Brillouin Scattering in a Plasma

We report the observation of an anti-Stokes satellite in the spectrum of light backscattered from a CO sub 2 laser plasma. Its origin is found to be Thomson scattering of the incident light from a counterpropagating mode-coupled plasma wave. The parent electron and ion waves in the mode-coupling process were simultaneously driven by stimulated Raman and Brillouin backscattering. The parent and daughter plasma waves were detected independently by ruby laser Thomson scattering. A computer simulation modeling the experiment shows further cascading of the backscattered light to lower frequencies, apparently due to rescattering of the backscattered light by another counterpropagating coupled mode. Comparisons with theoretical predictions are presented.