Brillouin-Backscattering from Plasma Produced by a Long CO₂-Laser Pulse

Abstract

Experimental studies were performed on the interactions of a CO2 laser beam of long pulse duration (∼50 ns FWHM) and peak power up to 4×1012 W/cm2 with plasma blobs produced by this laser from a massive planar target of aluminum or polyethylene. Special attention was paid to the laser reflectivity (R) due to the stimulated Brillouin backscattering (SBS), in particular to the correlation between the SBS reflectivity and the e-folding scale-length for spatial plasma density variation (L n ). It is shown that (1) the experimental L n -values are consistent with the theoretical ones predicted from an ellipsoidally-expanding self-regulating plasma model, and (2) taking those predicted L n -values into account, the experimental R-values agree well with those estimated from an existing simulation model, which is restricted to a relatively low percentage (15–20%) even for longer pulse duration.