Fluid and kinetic nonlinearities for back-stimulated Raman scattering driven by a broadband laser

Broadband lasers are anticipated to play a pivotal role in future direct-drive inertial confinement fusion experiments as an advanced driving scheme for suppressing laser-plasma instabilities (LPIs). However, the nonlinearities associated with broadband LPI remain incompletely understood. In this work, we conducted numerical simulations to investigate the nonlinearities of broadband laser-driven back-stimulated Raman scattering across various plasma densities. Our results demonstrate that, in the fluid nonlinearity-dominated regime, broadband lasers significantly reduce backscattered light and suppress Langmuir wave decay instability. In the kinetic nonlinearity-dominated regime, broadband lasers induce kinetic inflation and amplify the frequency shift of electron plasma waves. Additionally, we found that the intensity fluctuations of broadband lasers enhance electron trapping across a wide range of plasma densities, leading to the generation of more hot electrons.