Impact of electron trapping on stimulated Raman scattering under incoherent broadband laser light in homogeneous plasma

TL;DR

This paper investigates how increasing laser bandwidth affects stimulated Raman scattering in plasma, revealing that broad bandwidths do not suppress scattering in the kinetic inflation regime dominated by Landau damping.

Contribution

It demonstrates that broad laser bandwidths are ineffective in suppressing Raman scattering in the kinetic inflation regime, contrary to previous assumptions.

Findings

Broad bandwidth lasers do not significantly reduce Raman backscattering in the kinetic inflation regime.

Electron plasma wave matching broadens with increased laser bandwidth, maintaining high scattering levels.

Landau damping dominates the scattering process even with increased laser bandwidth.

Abstract

Backward stimulated Raman scattering is a three-wave coupling instability requiring the matching of an incoming pump light wave to a scattered light wave and electron plasma wave. It can be harmful to laser-driven inertial confinement fusion because of the reflection of a part of incident laser flux and the generation of suprathermal electrons that preheat the fuel. It is believed that by increasing the laser bandwidth one can suppress the excitation of Raman scattering and mitigate its detrimental effects. It is demonstrated in this paper that using a broad bandwidth laser has little effect on stimulated Raman scattering in the kinetic inflation regime where Landau damping dominates, as the additional bandwidth allows the electron plasma wave to match a wider range of laser frequencies. As a result, plasma wave saturation and Raman backscattering levels remain high even when the laser bandwidth is much larger than the effective instability growth rate.