From quantum to classical modelling of radiation reaction: a focus on the radiation spectrum

TL;DR

This paper explores the transition from quantum to classical models of radiation reaction in ultra-high-intensity laser interactions, focusing on photon spectrum predictions and the impact of quantum effects.

Contribution

It introduces a detailed analysis of radiation reaction models and links spectral predictions to electron distribution moments in the moderately quantum regime.

Findings

Quantum effects can cause spectrum hardening.

Spectrum evolution depends on laser and electron parameters.

Models connect photon spectrum to electron energy moments.

Abstract

Soon available multi petawatt ultra-high-intensity (UHI) lasers will allow us to probe high-amplitude electromagnetic fields interacting with either ultra-relativistic electron beams or hot plasmas in the so-called moderately quantum regime. The correct modelling of the back-reaction of high-energy photon emission on the radiating electron dynamics, a.k.a. radiation reaction, in this regime is a key point for UHI physics. This will lead to both validation of theoretical predictions on the photon spectrum emitted during the laser-particle interaction and to the generation of high energy photon sources. In this paper we analyse in detail such emission using recently developed models to account for radiation reaction. We show how the predictions on the spectrum can be linked to a reduced description of the electron distribution function in terms of the first energy moments. The temporal evolution of the spectrum is discussed, as well as the parameters for which quantum effects induce hardening of the spectrum.