# X-ray photon scattering at a focused high-intensity laser pulse

## TL;DR

This paper investigates x-ray photon scattering during head-on collisions with focused high-intensity laser pulses, exploring vacuum birefringence effects and how beam profile deformations influence the scattering signal.

## Contribution

It extends previous models by analyzing the impact of transverse focus profile deformations on x-ray scattering signals in high-intensity laser interactions.

## Key findings

- Vacuum birefringence manifests as polarization-flipped photons.
- Scattering signals can be detected outside the forward cone of the XFEL.
- Deformations of the focus profile affect the scattering signal distribution.

## Abstract

We study x-ray photon scattering in the head-on collision of an XFEL pulse and a focused high-intensity laser pulse, described as paraxial Laguerre-Gaussian beam of arbitrary mode composition. For adequately chosen relative orientations of the polarization vectors of the colliding laser fields, this gives rise to a vacuum birefringence effect manifesting itself in polarization flipped signal photons. Throughout this article the XFEL is assumed to be mildly focused to a waist larger than that of the high-intensity laser beam. As previously demonstrated for the special case of a fundamental paraxial Gaussian beam, this scenario is generically accompanied by a scattering phenomenon of x-ray energy signal photons outside the forward cone of the XFEL beam, potentially assisting the detection of the effect in experiment. Here, we study the fate of the x-ray scattering signal under exemplary deformations of the transverse focus profile of the high-intensity pump.