Laser photon merging in an electromagnetic field inhomogeneity

TL;DR

This paper investigates laser photon merging in inhomogeneous electromagnetic fields, deriving explicit results and analyzing the dominance of quantum reflection over merging, with implications for experimental detection.

Contribution

It introduces a systematic expansion of the photon polarization tensor in plane wave fields and analyzes photon merging versus quantum reflection in inhomogeneous fields.

Findings

Photon merging is dominated by quantum reflection in typical scenarios.

Proper polarization and filtering can enhance detection of merging signals.

A new systematic expansion of the photon polarization tensor is developed.

Abstract

We study the effect of laser photon merging, or equivalently high harmonic generation, in the quantum vacuum subject to inhomogeneous electromagnetic fields. Such a process is facilitated by the effective nonlinear couplings arising from charged particle-antiparticle fluctuations in the quantum vacuum subject to strong electromagnetic fields. We derive explicit results for general kinematic and polarization configurations involving optical photons. Concentrating on merged photons in reflected channels which are preferable in experiments for reasons of noise suppression, we demonstrate that photon merging is typically dominated by the competing nonlinear process of quantum reflection, though appropriate polarization and signal filtering could specifically search for the merging process. As a byproduct, we devise a novel systematic expansion of the photon polarization tensor in plane wave fields.