Single-photon cross sections σjk in units of 10−18 cm2, from experiment [26, 30] (bold), using the GIPPER codeprotecthyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32]

Table 1. Single-photon cross sections σjk in units of 10−18 cm2, from experiment [26, 30] (bold), using the GIPPER code\protect\hyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32].

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.