Ab initio calculations of two-electron emission by attosecond pulses

Abstract

Recent experimental developments of high-intensity, short-pulse XUV light sources are enhancing our ability to study electron-electron correlations. We perform time-dependent calculations to investigate the so-called "sequential" regime (ℏω > 54.4 eV) in the two-photon double ionization of helium. We show that attosecond pulses allow to not only probe but also to induce angular and energy correlations of the emitted electrons. Electron correlation induced by the time correlation between emission events manifests itself in the angular distribution of the ejected electrons. The final momentum distribution reveals regions dominated by the Wannier ridge break-up scenario and by post-collision interaction. In addition, we find evidence for an interference between direct ("nonsequential") and indirect ("sequential") double photo-ionization with intermediate shake-up states, the strength of which is controlled by the pulse duration. © 2009 IOP Publishing Ltd.