Stimulated Brillouin scattering of CO2 laser radiation from underdense plasma

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Abstract
Results of detailed measurements undertaken to compare experiment and theory of stimulated Brillouin scattering of high‐intensity CO2 laser radiation from underdense hydrogen and helium plasmas are reported. Spectral measurements confirm the ion acoustic wave as responsible for the backscatter. Ion Landau damping and collisions both contribute to spectral broadening. The maximum linear scattering growth rate γk was determined experimentally to be 6×1011 sec−1 in good agreement with a theoretical value calculated from random‐phase wave scattering. The value derived assuming coherent‐wave interaction was 1011 sec−1 which is a factor of 2 greater than the corresponding theoretical prediction. Temporal characteristics and reflectivity of the backscattered radiation are discussed.