Deep inner-shell multiphoton ionization by intense x-ray free-electron laser pulses

TL;DR

This study demonstrates multiphoton inner-shell ionization in argon and xenon atoms using intense x-ray free-electron laser pulses, revealing high charge states produced via multi-photon absorption at 5.5 keV.

Contribution

It introduces a new experimental and theoretical approach to study deep inner-shell multiphoton ionization in heavy atoms with XFELs.

Findings

Xenon ions up to +26 charge state via four-photon absorption

Argon ions up to +10 charge state via two-photon absorption

Determined XFEL pulse fluence using two-photon processes in argon

Abstract

We have investigated multiphoton multiple ionization dynamics of argon and xenon atoms using a new x-ray free electron laser (XFEL) facility, SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, and identified that highly charged Xe ions with the charge state up to +26 are produced predominantly via four-photon absorption as well as highly charged Ar ions with the charge state up to +10 are produced via two-photon absorption at a photon energy of 5.5 keV. The absolute fluence of the XFEL pulse, needed for comparison between theory and experiment, has been determined using two-photon processes in the argon atom with the help of benchmark ab initio calculations. Our experimental results, in combination with a newly developed theoretical model for heavy atoms, demonstrate the occurrence of multiphoton absorption involving deep inner shells.