EXPERIMENTAL-DETERMINATION OF THE ABSOLUTE VALUE OF THE TRIPLE DIFFERENTIAL CROSS-SECTION FOR DOUBLE PHOTOIONIZATION IN HELIUM

The absolute triple differential cross section (TDCS) for double photo ionization has been determined experimentally for the first time. The investigation was carried out for helium at a photon energy of 99 eV, for equal energy of the emitted electrons and in a plane perpendicular to the photon beam. Electron, ion and combined ion-electron spectrome try measurements were performed to put the data on an absolute scale. The result is compared with two recent calculations, and a parametriza tion is given which extends the TDCS obtained at one specific geometry to the whole space.