Coulomb focusing at above-threshold ionization in elliptically polarized mid-infrared strong laser fields

TL;DR

This paper investigates Coulomb focusing effects in above-threshold ionization under elliptically polarized mid-infrared laser fields, revealing how multiple scattering and Coulomb interactions influence electron spectra and ionization yields.

Contribution

It introduces a semiclassical model that captures Coulomb focusing effects, highlighting the role of multiple scattering and Coulomb influence at different ellipticities.

Findings

Coulomb focusing causes a low-energy structure in the photoelectron spectrum.

Multiple forward scattering dominates Coulomb focusing at moderate ellipticities.

Normalized ionization yield is enhanced at higher ellipticities due to Coulomb effects.

Abstract

The role of Coulomb focusing in above-threshold ionization in an elliptically polarized mid-infrared strong laser field is investigated within a semiclassical model incorporating tunneling and Coulomb field effects. It is shown that Coulomb focusing up to moderate ellipticity values is dominated by multiple forward scattering of the ionized electron by the atomic core that creates a characteristic low-energy structure in the photoelectron spectrum and is responsible for the peculiar energy scaling of the ionization normalized yield along the major polarization axis. At higher ellipticities, the electron continuum dynamics is disturbed by the Coulomb field effect mostly at the exit of the ionization tunnel. Due to the latter, the normalized yield is found to be enhanced, with the enhancement factor being sharply pronounced at intermediate ellipticities.