Nondipole circularly polarized laser-assisted photoelectron emission

TL;DR

This paper develops a theoretical framework for nondipole corrections in laser-assisted photoelectron emission using circularly polarized IR and XUV pulses, revealing new angular and momentum distribution features beyond the dipole approximation.

Contribution

It introduces the first-order nondipole correction theory for laser-assisted photoemission with circular polarization, analyzing the transition from dipole to nondipole regimes and identifying novel angular effects.

Findings

Nondipole effects cause asymmetry in photoelectron momentum distribution.

Identification of dipole forbidden directions with non-zero contributions.

Observation of Cooper-like minima in the angular distribution.

Abstract

We theoretically study atomic laser-assisted photoelectric emission (LAPE) beyond the electric dipole approximation. We present a theoretical description for first-order nondipole corrections ($O(c^{-1})$ where $c$ is the speed of light) to the nonrelativistic description of the laser-atom interaction for a strong circularly polarized infrared (IR) laser field combined with a train of extreme-ultraviolet (XUV) laser pulses. We investigate the photoelectron momentum distribution (PMD) as the product of two main contributions: the intra- and interpulse factors. Whereas the interpulse factor gives rise to a sideband pattern with a shift opposite to the IR beam propagation direction, the intrapulse factor forms an angular streaking pattern following the IR time-dependent polarization direction. We explore the transition of the PMD from the dipole to the nondipole framework, showing the gradual break of the forward-backward symmetry as the laser parameters are varied. Furthermore, we find non-zero contributions in dipole forbidden directions independent of the IR polarization state, wherein Cooper-\textit{like} minima are observed. Our work lays a theoretical foundation for understanding time-resolved nondipole LAPE in cutting-edge ultrafast experiments.