High-Intensity QED beyond the Locally Constant Field Approximation

Abstract

The locally constant field approximation (LCFA) underlies the numerical simulation of QED processes in plasma physics, astrophysics, and intense laser physics. The validity of the LCFA has been questioned in the parameter regime of current laser experiments, and improvements to it are needed. Using nonlinear Compton scattering in laser fields to illustrate, we show here how to overcome the problems inherent in corrections to the LCFA. We derive an "LCFA+" which, comparing with the full QED result, shows an improvement over the LCFA across the whole photon emission spectrum. We also demonstrate a numerical implementation of our results in the codes used to design and analyse intense laser experiments.