Beam focus and longitudinal polarization influence on spin dynamics in the Kapitza-Dirac effect

TL;DR

This paper theoretically examines how beam focusing and longitudinal polarization affect spin dynamics in the Kapitza-Dirac effect, revealing that focusing effects can be minimized with low beam foci.

Contribution

It introduces a relativistic Dirac equation approach to analyze the impact of longitudinal polarization and beam focusing on spin dynamics in Kapitza-Dirac scattering.

Findings

Longitudinal polarization effects scale with the square of the diffraction angle

Beam focusing influence can be negligible at low foci

Theoretical framework accounts for Gaussian beam profiles

Abstract

We theoretically investigate the influence of a longitudinal laser polarization component from beam focusing on spin dynamics in Kapitza-Dirac scattering by solving the relativistic Dirac equation with time-dependent perturbation theory. The transverse spacial dependence of the longitudinal beam polarization component is accounted for, by approximating a Gaussian beam with plane-wave components. We find that corrections from a longitudinal laser beam polarization component approximately scale with the second power of the diffraction angle $\epsilon$, from which we conclude that a related influence from beam focusing can be made negligibly small for sufficiently low beam foci.