Benchmarking semiclassical approaches to strong-field QED: nonlinear Compton scattering in intense laser pulses

TL;DR

This paper benchmarks semiclassical models against exact QED calculations for nonlinear Compton scattering in intense laser fields, demonstrating high accuracy at high intensities and discussing implications for QED cascade studies.

Contribution

It provides a comprehensive comparison of semiclassical approaches with exact QED results for nonlinear Compton scattering in intense laser pulses.

Findings

Percentage-level agreement in photon spectra

Accurate predictions for absorption from the background field at high intensities

Discussion of potential improvements in numerical methods

Abstract

The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as are found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes $a_0 > 5$. We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.