X-ray vacuum diffraction at finite spatio-temporal offset

TL;DR

This paper investigates the nonlinear quantum electrodynamics effect of x-ray vacuum diffraction caused by high-intensity laser and x-ray pulse collisions with finite spatio-temporal offsets, analyzing the phenomenon with Gaussian beam models.

Contribution

It provides a first-principles analysis of vacuum diffraction effects using Gaussian beam models, enhancing understanding of quantum vacuum nonlinearity signatures.

Findings

Signal photons are scattered outside the forward cone, indicating vacuum nonlinearity.

The angular distribution of the signal is sensitive to wavefront curvature.

Vacuum diffraction can help improve signal-to-background separation in experiments.

Abstract

We study the nonlinear QED signature of x-ray vacuum diffraction in the head-on collision of optical high-intensity and x-ray free-electron laser pulses at finite spatio-temporal offsets between the laser foci. The high-intensity laser driven scattering of signal photons outside the forward cone of the x-ray probe constitutes a prospective experimental signature of quantum vacuum nonlinearity. Resorting to a simplified phenomenological ad-hoc model, it was recently argued that the angular distribution of the signal in the far-field is sensitive to the wavefront curvature of the probe beam in the interaction region with the high-intensity pump. In this work, we model both the pump and probe fields as pulsed paraxial Gaussian beams and reanalyze this effect from first principles. We focus on vacuum diffraction both as an individual signature of quantum vacuum nonlinearity and as a potential means to improve the signal-to-background-separation in vacuum birefringence experiments.