Coherent forward stimulated Brillouin scattering of a spatially incoherent laser beam in a plasma and its effect on beam spray

TL;DR

This paper develops a statistical model for forward stimulated Brillouin scattering (FSBS) in incoherent laser beams in plasma, identifying a power threshold for coherent growth and proposing a new control metric for beam propagation.

Contribution

It introduces a novel statistical model for FSBS in incoherent beams, revealing a power threshold for coherent growth and beam spray onset, with implications for laser-plasma applications.

Findings

Existence of a power threshold below which incoherence suppresses FSBS

Confirmation of threshold and beam spray onset through 3D simulations

Proposal of a new figure of merit for controlling laser beam propagation in plasma

Abstract

A statistical model for forward stimulated Brillouin scattering (FSBS) is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. A threshold for the average power in a speckle is found, well below the self-focusing one, above which the laser beam spatial incoherence can not prevent the coherent growth of FSBS. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of the propagation through a plasma of a spatially incoherent laser beam.