Deep inner-shell multiphoton ionization by intense x-ray free-electron laser pulses
H. Fukuzawa et al.
Accepted
We have investigated multiphoton multiple ionization dynamics of xenon atoms using a new x-ray free electron laser (XFEL) facility, SPring-8 Ångstrom Compact free electron LAser (SACLA) in Japan, and identified that Xen+ with n up to 26 are produced at a photon energy of 5.5 keV. The observed high charge states (n 24) are produced via five-photon absorption, evidencing the occurrence of multiphoton absorption involving deep inner shells. A newly developed theoretical model, which shows good agreement with the experiment, elucidates the complex pathways of sequential electronic decay cascades accessible in heavy atoms. The present study of heavy-atom ionization dynamics in high-intensity hard-x-ray pulses makes a step forward towards molecular structure determination with XFELs.