10.6084/m9.figshare.1012453.v1 K Motomura K Motomura T Sakai T Sakai K Nagaya K Nagaya M Kimura M Kimura Y Ito Y Ito T Tachibana T Tachibana S Mondal S Mondal S-K Son S-K Son H Fukuzawa H Fukuzawa K Matsunami K Matsunami (a) Experimental configuration IOP Publishing 2013 compact XFEL pulse calculations point electron laser ionization ion spectrometer figure abstract xe argon atom sequential absorption fluence facility cross section Experimental configuration xenon atoms angstrom occurrence SACLA multiphoton charge states kev Atomic Physics Molecular Physics 2013-08-13 00:00:00 Figure https://iop.figshare.com/articles/figure/_a_Experimental_configuration/1012453 <p><strong>Figure 1.</strong> (a) Experimental configuration. (b) Cross section of the ion spectrometer.</p> <p><strong>Abstract</strong></p> <p>We have investigated multiphoton multiple ionization of argon and xenon atoms at 5 keV using a new x-ray free electron laser (XFEL) facility, the SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan. The experimental results are compared with the new theoretical results presented here. The absolute fluence of the XFEL pulse has been determined with the help of the calculations utilizing two-photon processes in the argon atom. The high charge states up to +22 observed for Xe in comparison with the calculations point to the occurrence of sequential <em>L</em>-shell multiphoton absorption and of resonance-enabled x-ray multiple ionization.</p>