Relativistic calculations of the non-resonant two-photon ionization of neutral atoms

TL;DR

This paper presents relativistic calculations of non-resonant two-photon ionization in neutral atoms, highlighting the significant impact of relativistic and screening effects on the ionization cross sections, with detailed results for several elements.

Contribution

It provides the first detailed relativistic and screening effect analysis on two-photon ionization cross sections for neutral atoms across multiple elements.

Findings

Relativistic effects halve the ionization cross section for uranium.

Screening effects cause a minimum in the cross section at the ionization threshold.

Relativistic and screening effects are crucial for accurate cross section predictions.

Abstract

The non-resonant two-photon one-electron ionization of neutral atoms is studied theoretically in the framework of relativistic second-order perturbation theory and independent particle approximation. In particular, the importance of relativistic and screening effects in the total two-photon ionization cross section is investigated. Detailed computations have been carried out for the K-shell ionization of neutral Ne, Ge, Xe, and U atoms. The relativistic effects significantly decrease the total cross section, for the case of U, for example, they reduce the total cross section by a factor of two. Moreover, we have found that the account for the screening effects of the remaining electrons leads to occurrence of an unexpected minimum in the total cross section at the total photon energies equal to the ionization threshold, for the case of Ne, for example, the cross section drops there by a factor of three.