Photo double ionization of He by circular and linear polarized single-photon absorption

We have measured absolute fully differential cross sections for photo double ionization of helium by circularly and linearly polarized light 20 eV above threshold. The data have been obtained by measuring in coincidence the momentum vector of the He2+ ion and one of the electrons, covering 4π solid angle for all particles. We give an overview over the momentum distribution in the three-body continuum and show fivefold differential cross sections. We find a swirl in the electron momentum space for double ionization by circularly polarized light. The present data supersede earlier data from our group (V mergel et al 1998 Phys. Rev. Lett. 80 5301). M This article features multimedia enhancements available from the abstract page in the online journal; see www.iop.org. (Some figures in this article are in colour only in the electronic version; see www.iop.org)