Measurements of Brillouin-Backscatter Dependence on Density-Scale Lengths near Critical Density

The Brillouin backscatter fraction was measured from laser-produced spherical plasmas with prepared scale lengths of from 5 to 50 μm. The scale lengths in the region of $0.1<~\frac{n}{n_c}<~1$ were measured using double-pulse holographic interferometry. The backscatter energy was found to vary from 5% to 25% of the incident energy over the range of scale lengths measured. The spectra of the backscatter light were obtained and show the red shifts characteristic of Brillouin scattering.