Brillouin and dielectric sidescatter of 10-μm light by a plasma

Sidescatter of CO2 laser light from underdense, laser-heated plasmas in H2 and He is observed at theta=900. Spectrum, exponentiation, isotropy, and polarization measurements are used to deconvolve two separate mechanisms: (1) Doppler-shifted reflections from moving dielectric discontinuities created in the laser-ionization process, and (2) Stimulated Brillouin scattering seeded by these reflections. The dielectric sidescatter is unpolarized and azimuthally symmetric, similar to the diffuse component of scattering in solid-target experiments. The Brillouin sidescatter saturates at a low level corresponding to an ion wave amplitude of 0.1--1.0%, consistent with previous data on the saturation of backscatter