Two-photon double ionization of He and Ne with intense VUV free-electron-laser pulses

Abstract

Two-photon double ionization of He and Ne by intense (1013-1014 W/cm2) short pulsed (∼ 25 fs) 44 eV radiation delivered by the free-electron LASer at Hamburg (FLASH) has been studied using a «Reaction Microscope». We observe characteristic signatures of direct (for He) and sequential (for Ne) ionization imprinted in different momentum distributions of the doubly charged ions. For Ne we also present kinematically complete data, extracting state-selective angular asymmetry parameters and an angular correlation function of both electrons, and compare them with recent theoretical predictions.