Saturation of the leading spike growth in backward Raman amplifiers

TL;DR

This paper investigates the maximum intensity achievable in backward Raman amplifiers, showing that relativistic electron nonlinearity causes early saturation of the leading spike, limiting the amplification before filamentation occurs.

Contribution

It introduces a simple analytical model for the saturation caused by relativistic nonlinearity, supported by numerical simulations, to determine the upper intensity limit in Raman amplification.

Findings

Relativistic nonlinearity causes early saturation of the leading spike.

The model predicts the upper limit for unfocused intensity.

Saturation occurs before filamentation instabilities develop.

Abstract

Backward Raman amplification of laser pulses in plasmas can produce nearly relativistic unfocused output intensities and multi-exawatt powers in compact devices. The largest achievable intensity depends on which of major competitive processes sets this limit. It is shown here that the relativistic electron nonlinearity can cause saturation of the leading amplified spike intensity before filamentation instabilities develop. A simple analytical model for the saturation, which supports numerical simulations, is suggested. The upper limit for the leading output spike unfocused intensity is calculated.