Experimental evidence of stimulated Raman re-scattering in laser-plasma interaction

TL;DR

This paper provides the first experimental evidence of stimulated Raman re-scattering in laser-plasma interactions, demonstrating that scattered light can undergo re-scattering, which has implications for inertial confinement fusion.

Contribution

It reports the first experimental observation of stimulated Raman re-scattering, confirming theoretical predictions and simulations in laser-plasma interactions relevant to fusion research.

Findings

Re-scattering of Raman scattered light observed experimentally.

Good agreement between simulations and experimental results.

Implications for laser-plasma interaction in inertial confinement fusion.

Abstract

We present the first experimental evidence of stimulated Raman re-scattering of a laser in plasma: The scattered light produced by the Raman instability is intense enough to scatter again through the same instability. Although never observed, re-scattering processes have been studied theoretically and numerically for many years in the context of inertial confinement fusion (ICF), since the plasma waves they generate could bootstrap thermal electrons to high energies [Phys. Rev. Lett. \textbf{110}, 165001 (2013)], preheating the fuel and degrading ignition conditions. Our experimental results are obtained with a spatially smoothed laser beam consisting of many speckles, with an average intensity around $10^{14}$ W/cm$^2$ and close to $10^{15}$ W/cm$^2$ in the speckles, such as those usually used in direct-drive ICF. Kinetic and hydrodynamic simulations show good agreement with the observations.