Radiative polarization of electrons in a strong laser wave

TL;DR

This paper reanalyzes electron radiative polarization in strong laser fields, confirming previous formulas, and finds polarization is limited to moderate energies with long polarization times, making practical polarization unfeasible.

Contribution

It provides an independent verification of polarization formulas and clarifies the conditions under which polarization occurs, highlighting limitations for practical applications.

Findings

Polarization exists mainly for electrons with energy $ ext{} extless 10$ and non-head-on collisions.

Maximum polarization degree can reach up to 65%.

Polarization time exceeds 1 second, making it practically unachievable.

Abstract

We reanalyze the problem of radiative polarization of electrons brought into collision with a circularly polarized strong plane wave. We present an independent analytical verification of formulae for the cross section given by D.\,Yu. Ivanov et al [Eur.\ Phys.\ J. C \textbf{36}, 127 (2004)]. By choosing the exact electron's helicity as the spin quantum number we show that the self-polarization effect exists only for the moderately relativistic electrons with energy $\gamma = E/mc^2 \lesssim 10$ and only for a non-head-on collision geometry. In these conditions polarization degree may achieve the values up to 65%, but the effective polarization time is found to be larger than 1\,s even for a high power optical or infrared laser with intensity parameter $\xi = |{\bf E}| m c^2/E_c \hbar \omega \sim 0.1$ ($E_c = m^2 c^3/e \hbar$). This makes such a polarization practically unrealizable. We also compare these results with the ones of some papers where the high degree of polarization was predicted for ultrarelativistic case. We argue that this apparent contradiction arises due to the different choice of the spin quantum numbers. In particular, the quantum numbers which provide the high polarization degree represent neither helicity nor transverse polarization, that makes the use of them inconvenient in practice.