Ultraviolet Thomson Scattering from Two-Plasmon--Decay Electron Plasma Waves Driven by Multiple Laser Beams

Thomson scattering is used to probe electron plasma waves (EPW's) driven by the common-wave two-plasmon--decay (TPD) instability near the quarter-critical density. Between two and five laser beams ($\lambda_{3\omega} = 351$ nm) illuminated planar CH targets with 300-$\mu $m-diam (FWHM) laser spots with overlapped intensities $\sim 10^{15}$ W/cm$^{2}$. A 263-nm Thomson-scattering beam was used to probe densities ranging from 0.2 to 0.25 $n_{\mathrm{c}}$ while $k$ matching the TPD common wave. The Thomson-scattering spectra show two spectral peaks consistent with scattering from forward-scattered TPD common-wave EPW's and Langmuir decay of backscattered TPD waves. Broad TPD driven spectral features were observed in an alternate scattering configuration probing EPW $k$ vectors that do not lie along a TPD maximum-growth hyperbola, consistent with TPD $k$-space saturation. Experimental results are compared to \textit{ZAK3D} simulations. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.