Mitigation of Inflationary Stimulated Raman Scattering with Laser Bandwidth

Kinetic inflation exacerbates the threat of the stimulated Raman scattering (SRS) instability to inertial confinement fusion. Continued growth of the instability requires phase matching between the incident light wave and the decay products, a scattered light wave, and an electron plasma wave (EPW). In principle, a density inhomogeneity can disrupt the phase matching by changing the frequency of the EPW along the gradient. In reality, electron trapping in the EPW produces a frequency shift that can compensate this change. This autoresonance, or kinetic inflation, can substantially enhance the SRS reflectivity. Here we demonstrate that laser bandwidth can mitigate inflationary SRS and limit the reflectivity to non-inflationary levels by rapidly moving the location of exact phase matching. While the instantaneous reflectivity depends on the local chirp of the incident light, the inflationary SRS threshold depends on the bandwidth format, for example random or smoothing by spectral dispersion. This leads to distinct scaling laws which can help guide SRS mitigation efforts.