Two-photon double ionization of Ne by free-electron laser radiation: a kinematically complete experiment

Abstract

We present kinematically complete data on two-photon double ionization of Ne induced by\nshort (∼25 fs) intense (∼5 × 1013 W cm−2) free-electron laser pulses at 44 eV. The observed\nelectron energy spectrum points to the dominance of ‘sequential’ ionization. We analyse\nstate-selective angular distributions as well as the two-electron angular correlation function,\nand suggest a method to determine the time delay between both ionization steps. The\nmeasured angular asymmetry ( ß-) parameters significantly deviate from the results of an\nearlier non-coincident experiment providing benchmark data for theory.