# Time-dependent configuration-interaction-singles calculation of the $5p$-subshell two-photon ionization cross section in xenon

## TL;DR

This paper uses a time-dependent configuration-interaction-singles method to calculate xenon's $5p$ two-photon ionization cross section below the one-photon threshold, comparing results with RPA and analyzing interchannel effects.

## Contribution

It introduces a time-dependent CI approach for two-photon ionization in xenon and compares it with RPA, highlighting the impact of interchannel coupling.

## Key findings

- TDCIS reproduces Rydberg state energies well.
- Interchannel coupling slightly alters the cross section.
- Results provide insights into multi-photon ionization processes.

## Abstract

The $5p$ two-photon ionization cross section of xenon in the photon-energy range below the one-photon ionization threshold is calculated within the time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS calculations are compared to random-phase-approximation (RPA) calculations [Wendin \textit{et al.}, J. Opt. Soc. Am. B \textbf{4}, 833 (1987)] and are found to reproduce the energy positions of the intermediate Rydberg states reasonably well. The effect of interchannel coupling is also investigated and found to change the cross section of the $5p$ shell only slightly compared to the intrachannel case.