Collective stimulated Brillouin scatter

TL;DR

This paper presents a new statistical theory for stimulated Brillouin backscatter (BSBS) in laser fusion plasma, revealing a collective regime with higher thresholds and implications for laser system design.

Contribution

It introduces a novel collective BSBS regime with a higher threshold and analyzes two distinct instability contributions in partially incoherent laser beams.

Findings

Identifies a collective BSBS regime with a higher threshold than classical models.

Shows the threshold is within the parameter space of NIF.

Suggests KrF-laser bandwidth can suppress BSBS effectively.

Abstract

We develop a statistical theory of stimulated Brillouin backscatter (BSBS) of a spatially and temporally partially incoherent laser beam for laser fusion relevant plasma. We find a new collective regime of BSBS which has a much larger threshold than the classical threshold of a coherent beam in long-scale-length laser fusion plasma. We identify two contributions to BSBS convective instability increment. The first is collective with intensity threshold independent of the laser correlation time and controlled by diffraction. The second is independent of diffraction, it grows with increase of the correlation time and does not have an intensity threshold. The instability threshold is inside the typical parameter region of National Ignition Facility (NIF). We also find that the bandwidth of KrF-laser-based fusion systems would be large enough to allow additional suppression of BSBS.