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 photoionization 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 spectrometry measurements were performed to put the on an absolute scale. The result is compared with two recent calculations, and a parametrization is given which extends the TDCS obtained at one specific geometry to the whole space. (author)