Vacuum birefringence in strong inhomogeneous electromagnetic fields

TL;DR

This paper develops an analytical framework to predict vacuum birefringence effects in strong, inhomogeneous electromagnetic fields, emphasizing the importance of interaction geometry for experimental detection with current laser and FEL facilities.

Contribution

It derives analytical solutions for vacuum birefringence considering realistic laser field structures and interaction geometries, enhancing precision in theoretical predictions.

Findings

Photon scattering depends strongly on interaction geometry.

Perpendicular scattered photons can be detected outside the incident beam cone.

The framework facilitates experimental tests of non-linear QED effects.

Abstract

Birefringence is one of the fascinating properties of the vacuum of quantum electrodynamics (QED) in strong electromagnetic fields. The scattering of linearly polarized incident probe photons into a perpendicularly polarized mode provides a distinct signature of the optical activity of the quantum vacuum and thus offers an excellent opportunity for a precision test of non-linear QED. Precision tests require accurate predictions and thus a theoretical framework that is capable of taking the detailed experimental geometry into account. We derive analytical solutions for vacuum birefringence which include the spatio-temporal field structure of a strong optical pump laser field and an x-ray probe. We show that the angular distribution of the scattered photons depends strongly on the interaction geometry and find that scattering of the perpendicularly polarized scattered photons out of the cone of the incident probe x-ray beam is the key to making the phenomenon experimentally accessible with the current generation of FEL/high-field laser facilities.