Optical Mixing Controlled Stimulated Scattering instabilities: Suppression of SRS by the Controlled Introduction of Ion Acoustic and Electron Plasma Wave Turbulence

TL;DR

This paper demonstrates that controlled optical mixing of laser beams can suppress stimulated Raman scattering (SRS) instabilities in plasma, with potential applications for improving laser-driven fusion experiments.

Contribution

It introduces a method to suppress SRS by externally controlling ion acoustic and electron plasma wave turbulence through optical mixing techniques.

Findings

SRS suppression achieved in prescribed spectral windows

Green beam amplification observed when crossed with blue pump

Potential for reducing SRS in large-scale hohlraum experiments

Abstract

In a series of experiments on the Omega laser facility at LLE, we have demonstrated the suppression of SRS in prescribed spectral windows due to the presence of externally controlled levels of ion acoustic waves (IAW, by crossing two blue beams at the Mach -1 surface) and electron plasma waves (EPW, by crossing a blue and a green beam around a tenth critical density plasma) generated via optical mixing. We have further observed SRS backscattering of a green beam when crossed with a blue pump beam, in whose absence, that (green beam) backscattering signature was five times smaller. This is direct evidence for green beam amplification when crossed with the blue. Additional proof comes from transmitted green beam measurements. A combination of these techniques may allow the suppression of unacceptable levels of SRS near the light entrance hole of large-scale hohlraums on the NIF or LMJ.