Many-electron character of two-photon above-threshold ionization of Ar

TL;DR

This study investigates the many-electron effects in two-photon above-threshold ionization of argon, revealing significant correlation impacts on cross sections and resonances, supported by advanced theoretical calculations.

Contribution

The paper extends the correlation function technique to continuum states and demonstrates the dominant role of many-electron correlations in argon ionization near the $3p^{4}$ threshold.

Findings

Cross sections increase by over a factor of 3 due to correlations.

Resonances appear in the photon energy range of doubly-excited states.

Good agreement between length and velocity form calculations.

Abstract

The absolute generalized cross sections and angular distribution parameters of photoelectrons for the two-photon above threshold $3p$-ionization of Ar were calculated in the exciting photon energy range from 15.76 to 36 eV. The correlation function technique developed earlier was extended for the case when an intermediate-state function is of a continuum-type. We show that two-photon ionization of Ar near the $3p^{4}$ threshold to a large extent is determined by the $(3p\dashrightarrow\varepsilon d)^{2}$ two-photon absorption via the giant resonance. This many-electron correlation causes (i) an increase of the photoionization cross sections by more than a factor of 3; (ii) the appearance of resonances in the exciting-photon energy range of the doubly-excited states. The predictions are supported by a good agreement between length and velocity results obtained after taking into account of the higher-order perturbation theory corrections.