On efficiency of double ionization of a three-electron atom in moderate laser field intensities

TL;DR

This study investigates the double ionization process in a three-electron atom under moderate laser fields, revealing a shifted ionization yield 'knee' due to recollision-excitation channels involving inner orbital electrons.

Contribution

A semi-analytic model combining multiple ionization channels was developed to explain the shifted double ionization 'knee' in three-electron atoms under laser fields.

Findings

The 'knee' appears at lower intensities than in two-electron systems.

Recollision-excitation from inner orbitals dominates the shifted 'knee'.

The model aligns with ab initio simulation results.

Abstract

We study double ionization in a one-dimensional model of a three-electron atom exposed to strong short laser fields. The corresponding ab initio simulations reveal a characteristic ``knee'' in the ionization yield at lower field intensities than in comparable two-electron systems. To understand the origin of this shift, a quantitative semi-analytic model for double ionization of a three-electron atom has been created. In this model, ionization is treated as a combination of different scenarios and channels. Each channel is simulated with either Quantitative Rescattering Theory (QRS) or two-electron ab initio model. Analysis of the semi-analytical results indicates that the shifted part of the ``knee'' is dominated by a recollision-excitation channel in which the rescattering electron initially escapes the parent atom from an inner orbital. This counterintuitive phenomenon is then discussed and explained.