TY - DATA T1 - Experimental setup for the investigation of atoms by ion TOF spectroscopy in an FEL focus of a spherical narrow-bandwidth multilayer mirror PY - 2013/08/13 AU - R Guichard AU - M Richter AU - J-M Rost AU - U Saalmann AU - A A Sorokin AU - K Tiedtke UR - https://iop.figshare.com/articles/figure/_Experimental_setup_for_the_investigation_of_atoms_by_ion_TOF_spectroscopy_in_an_FEL_focus_of_a_sphe/1012460 DO - 10.6084/m9.figshare.1012460.v1 L4 - https://ndownloader.figshare.com/files/1480282 KW - ion TOF spectroscopy KW - model KW - photon energies KW - ion charge states KW - rate equations KW - neon atoms KW - photoionization channels KW - laser beam KW - photoionization yields KW - FEL focus KW - intensity distribution KW - sequential photoionization KW - flash KW - ionization yields KW - Atomic Physics KW - Molecular Physics N2 - Figure 1. Experimental setup for the investigation of atoms by ion TOF spectroscopy in an FEL focus of a spherical narrow-bandwidth multilayer mirror. Abstract At the free-electron laser FLASH, multiple ionization of neon atoms was quantitatively investigated at photon energies of 93.0 and 90.5 eV. For ion charge states up to 6+, we compare the respective absolute photoionization yields with results from a minimal model and an elaborate description including standard sequential and direct photoionization channels. Both approaches are based on rate equations and take into account a Gaussian spatial intensity distribution of the laser beam. From the comparison we conclude that photoionization up to a charge of 5+ can be described by the minimal model which we interpret as sequential photoionization assisted by electron shake-up processes. For higher charges, the experimental ionization yields systematically exceed the elaborate rate-based prediction. ER -