ANGULAR-DISTRIBUTIONS FOR DOUBLE PHOTOIONIZATION OF HELIUM - A COMPARATIVE-STUDY

We have performed calculations of the triply differential cross sectio n (TDCS) for double photoionization of helium. Our calculations are ba sed on two different nb initio methods, one where the final continuum state is represented by a product of three Coulomb wavefunctions, with the dipole matrix element evaluated directly, the other where the fin al state is represented by a product of two screened Coulomb wavefunct ions, which is substituted into a Bur formula that in principle yields exact results. We compare the results of the two calculations with ea ch other and also with two different sets of experimental data, for va rious geometries, for various ratios of the energies of the two photoe lectrons, and for various photon energies such that the total energy o f the photoelectrons ranges from 0.6-20 eV above threshold. The theore tical results for the shapes of the TDCS are in good agreement with th e experimental data and also with each other, although the calculated absolute values of the TDCS differ. We comment on various features of the angular distributions.