# Ultrarelativistic electron beam polarization in single-shot interaction with an ultraintense laser pulse

## TL;DR

This paper demonstrates how an ultraintense laser pulse can rapidly polarize an ultrarelativistic electron beam through spin-dependent radiation reaction, enabling generation of highly polarized beams in femtoseconds.

## Contribution

It introduces a Monte-Carlo method to model electron spin effects in intense fields and shows how laser pulses can polarize electron beams via quantum radiation reaction.

## Key findings

- Electron beams can be polarized to over 70% within tens of femtoseconds.
- Elliptically polarized laser pulses induce spin-dependent splitting of electron beams.
- The method is feasible with current laser technology.

## Abstract

Spin-polarization of an ultrarelativistic electron beam head-on colliding with an ultraintense laser pulse is investigated in the quantum radiation-reaction regime. We develop a Monte-Carlo method to model electron radiative spin effects in arbitrary electromagnetic fields by employing spin-resolved radiation probabilities in the local constant field approximation. Due to spin-dependent radiation reaction, the applied elliptically polarized laser pulse polarizes the initially unpolarized electron beam and splits it along the propagation direction into two oppositely transversely polarized parts with a splitting angle of about tens of milliradians. Thus, a dense electron beam with above 70\% polarization can be generated in tens of femtoseconds. The proposed method demonstrates a way for relativistic electron beam polarization with currently achievable laser facilities.