Probing vacuum birefringence using x-ray free electron and optical high-intensity lasers

TL;DR

This paper provides a detailed theoretical analysis and realistic modeling of an experiment to detect vacuum birefringence using x-ray free electron lasers and high-intensity optical lasers, aiming to improve detection strategies.

Contribution

It advances previous work by incorporating realistic laser pulse descriptions and additional effects, enabling precise predictions and optimization of the experimental signal.

Findings

Quantitative predictions for vacuum birefringence signal

Optimized experimental parameters for detection

Enhanced understanding of laser field effects

Abstract

Vacuum birefringence is one of the most striking predictions of strong field quantum electrodynamics: Probe photons traversing a strong field region can indirectly sense the applied "pump" electromagnetic field via quantum fluctuations of virtual charged particles which couple to both pump and probe fields. This coupling is sensitive to the field alignment and can effectively result in two different indices of refraction for the probe photon polarization modes giving rise to a birefringence phenomenon. In this article we perform a dedicated theoretical analysis of the proposed discovery experiment of vacuum birefringence at a x-ray free electron laser/optical high-intensity laser facility. Describing both pump and probe laser pulses realistically in terms of their macroscopic electromagnetic fields, we go beyond previous analyses by accounting for various effects not considered before in this context. Our study facilitates stringent quantitative predictions and optimizations of the signal in an actual experiment.