Two-photon sweeping out of the K-shell of a heavy atomic ion

TL;DR

This paper predicts that two-photon double ionization of a heavy atomic ion's K-shell has a significantly higher cross-section at high photon energies, suggesting new experimental avenues with X-ray free-electron lasers.

Contribution

The study introduces a theoretical framework for calculating generalized cross-sections of two-photon K-shell ionization in heavy ions, incorporating advanced quantum perturbation and wave function methods.

Findings

High-energy (≥15.8 keV) two-photon ionization cross-section exceeds single ionization by several orders of magnitude.

Predicted results align qualitatively with previous work, confirming the significance of two-photon processes.

Proposes experimental setup using polarized X-ray photons to test the predictions.

Abstract

Within the framework of the second-order non-relativistic quantum perturbation theory, the methods of the theory of irreducible tensor operators, and nonorthogonal orbitals, the absolute values and shape of the generalized cross-sections of the two-photon double ionization (sweeping) of the K-shell of a heavy neon-like ion of an iron atom were predicted. The complete wave functions of the ground state of the ion and the states of its ionization are obtained in the single-configuration Hartree-Fock approximation. The effects of radial relaxation of ionization states in the field of one and two vacancies in the K-shell are taken into account. The matrix element of the operator of the radiation transition between continuum-spectrum states is taken into account by introducing a correlation function. It was established that the generalized cross-section of the two-photon sweeping of the K-shell at high (greater than or equal to 15.8 keV) energies of absorbed X-ray photons is several orders of magnitude greater than the generalized cross-section of the two-photon single ionization of the K-shell. This result qualitatively reproduces the work of Novikov S.A. and Hopersky A.N. (J. Phys. B 2002. V. 35. P. L339), stimulates future research, in particular, the effects of cascade "evaporation" of electron shells of an atom (atomic ion) when filling an empty K-shell and can be tested in X-ray free-electron laser experiments with high peak radiation brightness and ultrashort photon pulse duration. The scheme of the proposed experiment with two linearly polarized X-ray photons is presented.