Nondipole circularly polarized laser-assisted photoelectron emission

Abstract

We theoretically study atomic laser-assisted photoelectric emission (LAPE) beyond the electric dipole approximation. We present a theoretical description based on the strong-field approximation (SFA) for first-order nondipole corrections [O(1/c)] 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 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-like minima are observed. Our work lays a theoretical foundation for understanding time-resolved nondipole LAPE in cutting-edge ultrafast experiments.