Nondipole signatures in ionization

TL;DR

This paper introduces a numerical method for solving the time-dependent Schrödinger equation to study nondipole effects in laser-induced ionization, revealing how these effects influence electron dynamics and harmonic generation.

Contribution

A novel numerical approach based on the Suzuki-Trotter scheme that efficiently incorporates nondipole effects in laser-matter interaction simulations.

Findings

Even-order harmonics are generated along the laser polarization direction.

Nondipole effects cause low-energy electrons to be emitted opposite to the laser propagation.

Rescattering processes dominate at low frequencies, less so at high frequencies.

Abstract

A general method for solving numerically the time-dependent Schr\"odinger equation, that is based on the Suzuki-Trotter scheme with the split-step Fourier approach, is introduced. The method relies on a Hamiltonian decomposition, where except of the components depending exclusively on the momentum or on the position operators, there are also terms depending on both momentum and position operators in particular configurations. We demonstrate that, for as long as the latter does not depend on noncommuting coordinates of the momentum and position operators, nondipole effects in laser-matter interactions can be studied without applying extra unitary operations. Specifically, we analyze the effect of nondipole corrections in ionization of a two-dimensional hydrogen atom for low- and high-frequency pulses. In the former case, the electron wave packet dynamics is dominated by rescattering processes within the laser pulse, leading to the high-order harmonic generation. We illustrate that harmonics of even orders are generated in the direction of the laser field polarization. On the contrary, for high-frequency pulses, such rescattering processes can be neglected. We demonstrate that a significant portion of the low-energy photoelectrons is detected opposite to the laser pulse propagation direction as a consequence of their post-pulse wave packet spreading and interaction with the parent ion.