Quantum-orbit analysis of above threshold ionization by intense spatially inhomogeneous field

TL;DR

This paper analyzes above threshold ionization in atoms under intense spatially inhomogeneous laser fields, revealing how inhomogeneity affects quantum orbits, ionization times, and electron spectra beyond traditional models.

Contribution

It introduces a detailed quantum orbit analysis of ATI in inhomogeneous fields, showing significant differences from homogeneous field behavior and extending the ATI cutoff beyond semiclassical predictions.

Findings

Inhomogeneous fields cause ionization and rescattering times to differ between cycles.

The ATI cutoff extends beyond the semiclassical limit with increased inhomogeneity.

Electron momentum distributions vary significantly between neighboring cycles.

Abstract

We perform a detailed analysis of above threshold ionization (ATI) in atoms within the strong field approximation (SFA) by considering spatially inhomogeneous monochromatic laser fields. The locally enhanced field induced by resonance plasmons is an example for such inhomogeneous fields. We investigate how the individual pairs of quantum orbits contribute to the photoelectron spectra and the angular electron momentum distributions. We demonstrate that the quantum orbits have a very different behavior in the spatially inhomogeneous field when compared to the homogeneous field. In the case of inhomogeneous fields, the ionization and rescattering times differ between neighboring cycles, despite the field being monochromatic. Indeed, the contributions from one cycle may lead to a lower cutoff, while another may develop a higher cutoff. Within our model, we show that the ATI cutoff extends far beyond the semiclassical cutoff, as a function of inhomogeneity strength. Furthermore, the angular momentum distributions have very different features compared to the homogeneous case. For the neighboring cycles, the electron momentum distributions do not share the same absolute momentum, and they do not have the same yield