Comparison study of electron correlation in one-photon and two-photon double ionization of helium

Abstract

Based on ab initio time-dependent calculations for helium, we study the joint angular distribution (JAD) of the two electrons ionized by absorbing one or two photons. On the JAD plane for the equal energy sharing case, one can identify a common symmetric ejection mode with respect to the laser polarization for three different processes, i.e., one-photon double ionization, two-photon nonsequential ionization, and sequential double ionization. In this symmetric ejection case, the two ejected electrons strongly favor a particular interelectron angle. We show that this angle can mimic the electron correlation strength in these double-ionization processes. The interelectron angle in the three types of double ionization is found to be obviously different.