Calculation of multiphoton ionization amplitudes and cross sections of few-electron atoms

TL;DR

This paper introduces a theoretical method to calculate multiphoton ionization amplitudes and cross sections for few-electron atoms, applicable across a range of photon energies and including resonance effects.

Contribution

The novel approach extracts partial wave amplitudes from scattering wave functions using Coulomb wave descriptions, enabling calculations for multiphoton ionization processes.

Findings

Calculated multiphoton ionization cross sections for hydrogen and helium.

Determined photoelectron angular distribution asymmetry parameters.

Applicable to photon energies below and above ionization thresholds.

Abstract

We present a theoretical method for calculating multiphoton ionization amplitudes and cross sections of few-electron atoms. The present approach is based on an extraction of partial wave amplitudes from a scattering wave function, which is calculated by solving a system of driven Schroedinger equations. The extraction relies on a description of partial waves in terms of a small number of Coulomb waves with fixed wave numbers. The method can be used for photon energies below and above the ionization threshold and to treat resonance-enhanced multiphoton ionization. We use it to calculate two-, three-, and four-photon ionization cross sections of hydrogen and helium atoms for a wide range of photon energies and to determine the asymmetry parameters of photoelectron angular distributions for two-, three-, and four-photon ionization of the helium atom.