Resonant scattering of plane-wave and twisted photons at the Gamma Factory

TL;DR

This paper theoretically investigates the resonant elastic scattering of laser photons by ultra-relativistic ions, focusing on angular distribution and polarization, including the effects of twisted photons with orbital angular momentum.

Contribution

It develops a general approach using polarization tensors to describe scattering properties for arbitrary relativistic ions and explores scattering of both plane-wave and twisted photons.

Findings

Derived relations between incident and scattered photon polarization states.

Analyzed angular distribution of scattered photons for various resonant transitions.

Discussed conditions under which scattered photons retain orbital angular momentum.

Abstract

We present a theoretical investigation of the resonant elastic scattering of laser photons by ultra-relativistic partially stripped ions, that is the core process of the Gamma Factory project. Special emphasis in our study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion-rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many-electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization tensors we explore in detail the scattering of both, conventional plane-wave- and twisted (or vortex) photons. For the former case we show how the propagation directions and polarization states of incident and outgoing photons are related to each other for the $n S_{0} \to n' P_{1} \to n S_{0}$, $n S_{1/2} \to n' P_{1/2} \to n S_{1/2}$ and $n S_{1/2} \to n' P_{3/2} \to n S_{1/2}$ resonant transitions. For the scattering of initially twisted light, that carries non-zero orbital angular momentum, we explore the angular distribution of secondary photons and discuss the conditions under which they are also twisted.