# Nonlinear effects in photoionization over a broad photon-energy range within the TDCIS scheme

## TL;DR

This paper reviews the TDCIS method for modeling nonlinear photoionization across a broad photon-energy spectrum, highlighting its application to argon and xenon, and exploring phenomena like giant resonances and multiphoton ionization in the x-ray regime.

## Contribution

It provides a comprehensive tutorial on the TDCIS scheme's application to nonlinear ionization, including wave function propagation, photoelectron spectra calculation, and analysis of high-energy phenomena.

## Key findings

- Analysis of xenon 4d giant dipole resonance reveals resonance substructure.
- Identification of the intensity threshold for multiphoton ionization at hard x-ray energies.
- Application of TDCIS demonstrates its effectiveness across a broad photon-energy range.

## Abstract

The present tutorial provides an overview of the time-dependent configuration interaction singles (\acs{TDCIS}) scheme applied to nonlinear ionization over a broad photon-energy range. The efficient propagation of the wave function and the calculation of photoelectron spectra within this approach are described and demonstrated in various applications. Above-threshold ionization of argon and xenon in the extreme ultraviolet energy range is investigated as an example. A particular focus is put on the xenon $4d$ giant dipole resonance and the information that nonlinear ionization can provide about resonance substructure. Furthermore, above-threshold ionization is studied in the x-ray regime and the intensity regime, at which multiphoton ionization starts to play a role at hard x-ray photon energies, is identified.