Role of spatiotemporal couplings in stimulated Raman side scattering

Abstract

A high-intensity laser pulse propagating through underdense plasma is prone to parametric instabilities. We report on experiments investigating the influence of a pulse-front tilt (PFT), one of the most common spatiotemporal couplings in the laser focus, on stimulated Raman side scattering (SRSS). For a laser pulse exhibiting such a PFT, SRSS becomes asymmetric, varies as the pulse propagates through the plasma, and yields larger scattering angles than expected from traditional SRSS theory, indicating a correlation of the scattering with the PFT. We show that by including the propagation of a Gaussian laser pulse with a PFT in an analytical model, we can describe the observed asymmetric side scattering. Two-dimensional particle-in-cell simulations reproduce the observed scattering and the asymmetry induced by the PFT. A microscopic analysis of the simulation data shows that the sum of the angles from PFT and SRSS describe the observed side scattering.