Observations of Transition to Strongly Coupled Stimulated Brillouin Scattering in Laser-Plasma Interactions

Scattered light near the laser wavelength has been spectrally and temporally resolved in experiments in which a 1.06 μm wavelength laser irradiates a low-$Z$ target. At sufficiently high laser intensities, the backscattered spectrum broadens toward longer wavelengths (lower frequencies) by an amount which is several times an ion acoustic shift. The behavior of the spectra agrees well with the prediction of time-dependent, homogeneous theory.