Signatures of vacuum birefringence in low-power flying focus pulses

TL;DR

This paper proposes a novel method using flying focus laser pulses to detect vacuum birefringence at lower laser powers, making experimental observation more feasible with current technology.

Contribution

It introduces a scheme utilizing programmable flying focus pulses to enhance vacuum birefringence detection, reducing the required laser power for observable effects.

Findings

Induces polarization ellipticity of ~10^{-10} in x-ray probe

Overcomes power barriers for vacuum birefringence detection

Compatible with existing x-ray polarimeters

Abstract

Vacuum birefringence produces a differential phase between orthogonally polarized components of a weak electromagnetic probe in the presence of a strong electromagnetic field. Despite representing a hallmark prediction of quantum electrodynamics, vacuum birefringence remains untested in pure light configurations due to the extremely large electromagnetic fields required for a detectable phase difference. Here, we exploit the programmable focal velocity and extended focal range of a flying focus laser pulse to substantially lower the laser power required for detection of vacuum birefringence. In the proposed scheme, a linearly polarized x-ray probe pulse counter-propagates with respect to a flying focus pulse, whose focus moves at the speed of light in the same direction as the x-ray probe. The peak intensity of the flying focus pulse overlaps the probe over millimeter-scale distances and induces a polarization ellipticity on the order of $10^{-10}$, which lies within the detection sensitivity of existing x-ray polarimeters.