Nonsequential Two-Photon Double Ionization of Atoms: Identifying the Mechanism

TL;DR

This paper introduces a simplified model for nonsequential two-photon double ionization of atoms, accurately predicting cross sections and providing insight into the physical mechanism, validated against ab initio calculations.

Contribution

The paper presents a new approximate model that effectively describes nonsequential two-photon double ionization, matching detailed ab initio results and extending to neon.

Findings

Model accurately predicts helium ionization cross sections

Agreement with ab initio calculations at a quantitative level

Extended predictions to neon in the nonsequential regime

Abstract

We develop an approximate model for the process of direct (nonsequential) two-photon double ionization of atoms. Employing the model, we calculate (generalized) total cross sections as well as energy-resolved differential cross sections of helium for photon energies ranging from 39 to 54 eV. A comparison with results of \textit{ab initio} calculations reveals that the agreement is at a quantitative level. We thus demonstrate that this complex ionization process is fully described by the simple model, providing insight into the underlying physical mechanism. Finally, we use the model to calculate generalized cross sections for the two-photon double ionization of neon in the nonsequential regime.