# Polarized positron beams via intense two-color laser pulses

## TL;DR

This paper presents a theoretical study demonstrating that intense two-color laser pulses can generate highly polarized ultrarelativistic positron beams with significant polarization, low divergence, and high density, within femtosecond timescales.

## Contribution

It introduces a novel method using two-color laser pulses to produce polarized positrons, leveraging spin asymmetries in pair production processes in strong fields.

## Key findings

- Positron beams with approximately 60% polarization can be generated.
- The produced positrons have a small angular divergence of about 74 mrad.
- The density of the positron beam can reach approximately 10^14 cm^-3.

## Abstract

Generation of ultrarelativistic polarized positrons during interaction of an ultrarelativistic electron beam with a counterpropagating two-color petawatt laser pulse is investigated theoretically. Our Monte Carlo simulation based on a semi-classical model, incorporates photon emissions and pair productions, using spin-resolved quantum probabilities in the local constant field approximation, and describes the polarization of electrons and positrons for the pair production and photon emission processes, as well as the classical spin precession in-between. The main reason of the polarization is shown to be the spin-asymmetry of the pair production process in strong external fields, combined with the asymmetry of the two-color laser field. Employing a feasible scenario, we show that highly polarized positron beams, with a polarization degree of $\zeta\approx 60\%$, can be produced in a femtosecond time scale, with a small angular divergence, $\sim 74$ mrad, and high density $\sim 10^{14}$ cm$^{-3}$. The laser-driven positron source, along with laser wakefield acceleration, may pave the way to small scale facilities for high energy physics studies.