Signatures of autoionization in the angular electron distribution in two-photon double ionization of Ar

Abstract

A kinematically complete experiment on two-photon double ionization of Ar by free-electron laser radiation with a photon energy of 27.93 eV was performed. The electron energy spectra show that double ionization is dominated by the sequential process. Comparison of the electron angular distributions to our data for single ionization and to theory confirms that even in the sequential process the electrons from both ionization steps are correlated with each other through polarization of the intermediate Ar + state. Furthermore, a very important role of auto-ionization in both ionization steps is found.

Electron-ion coincidence measurements of molecular dynamics with intense X-ray pulses

“…They are expected to open up a variety of new possibilities for imaging molecular dynamics at X-ray free-electron lasers (XFELs), in particular, enabling channel-selective and molecular-frame measurements 5 . However, this method has been implemented in only a few experiments at free-electron laser (FEL) facilities to date [6][7][8][9] , largely hindered by its requirement of low interaction rates (less than one interaction event per laser shot). With several high-repetition rate X-ray freeelectron lasers now coming into operation, electron-ion coincidence measurements are becoming a more feasible approach 10 that can take full advantage of the envisioned MHz repetition rates in order to significantly increase the information content of the experiments.…”

Atomic, Molecular and Cluster Science with the Reaction Microscope Endstation at FLASH2

“…Momentum conservation in three-dimension is used to sort out all particles originating from the same fragmenting target particle, that is finding coincident particles. Angle-and energy-resolved measurements of charged particles in multi-coincidence are the key features of the REMI and enable to investigate atomic and molecular processes in detail [5,6,29,30].…”

“…In a kinematically complete experiment, double ionization of argon by absorption of two photons was measured [30]. Neutral argon atoms were irradiated by FEL radiation with a photon energy of 27.93 eV (averaged peak intensity (3 ± 2) × 10 13 W/cm 2 , pulse duration approximately 50 fs).…”

Near-threshold two-photon double ionization of Kr in the vacuum ultraviolet

“…In that case the photon energy of the FLASH FEL was tuned to five specific values in the range from 38 to 91 eV and the experimental results were compared with theoretical calculations provided by Fritzsche et al [28,29] and Kheifets et al [30]. A few other experiments on PADs in multiphoton double ionization in FEL fields exist [31][32][33][34][35][36]. The early studies on the sequential ionization in noble gases are outlined in Ref.…”

“…[39]. The present work was motivated by an experiment on TPDI in Ar [31] where only the 3 P term of the rm3p 4 configuration of Ar 2+ was accessible to the FEL photon energy used. The 2 P term of the 3p 5 configuration was also accessible in the first step but it was not possible to resolve the individual 3 P2,1,0 spin-orbit split terms.…”