# Ultrafast Polarization of an Electron Beam in an Intense Bi-chromatic Laser Field

## TL;DR

This paper demonstrates ultrafast radiative polarization of high-energy electron beams using intense bi-chromatic laser fields, combining kinetic and quantum Monte Carlo simulations to optimize conditions and predict measurable spin effects.

## Contribution

It introduces a combined kinetic and quantum Monte Carlo approach to simulate and optimize ultrafast electron beam polarization in high-intensity laser fields.

## Key findings

- Maximum polarization achieved under specific laser parameters.
- Predicted 5% energy splitting between spin states.
- Feasible experimental setup for verifying ultrafast polarization.

## Abstract

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.