Low Stimulated Brillouin Backscatter Observed from Large, Hot Plasmas in Gas-Filled Hohlraums

Stimulated Brillouin scattering (SBS) has been measured from hohlraums with plasma conditions similar to those predicted for high gain targets. The plasmas differ from the more familiar exploding foil or solid targets in being hot (3 keV), high electron density (1$0^{21}$ c${\mathrm{m}}^{–3}$), stationary, confined within a gold cylinder, and uniform over greater than 2 mm. Peak SBS backscatter is <3% in these hohlraums for an interaction beam with intensities of $\left(1-4\right)\times {10}^{15}$ W/c${\mathrm{m}}^2$, laser wavelength equal to 0.351 μm, $f/4\mathrm{}$ or $f/8\mathrm{}$ focusing optics, and a variety of beam smoothing implementations.