Kapitza-Dirac effect in the relativistic regime

TL;DR

This paper provides a relativistic quantum analysis of the Kapitza-Dirac effect, revealing spin-flip phenomena and spin rotation effects during electron-laser interactions in the Bragg regime, supported by numerical and perturbative solutions.

Contribution

It introduces a relativistic framework for the Kapitza-Dirac effect, including explicit spin rotation descriptions and generalized Rabi theory for off-resonant cases.

Findings

Spin-flips occur in two- and three-photon regimes under certain parameters.

Electron spin is rotated during laser interaction, with explicit rotation axis and angle.

Off-resonant effects are described by a generalized Rabi theory.

Abstract

A relativistic description of the Kapitza-Dirac effect in the so-called Bragg regime with two and three interacting photons is presented by investigating both numerical and perturbative solutions of the Dirac equation in momentum space. We demonstrate that spin-flips can be observed in the two-photon and the three-photon Kapitza-Dirac effect for certain parameters. During the interaction with the laser field the electron's spin is rotated, and we give explicit expressions for the rotation axis and the rotation angle. The off-resonant Kapitza-Dirac effect, that is, when the Bragg condition is not exactly fulfilled, is described by a generalized Rabi theory. We also analyze the in-field quantum dynamics as obtained from the numerical solution of the Dirac equation.