Experimental determination of the absolute value of the triple differential cross section for double photoionization in helium

Abstract

The recent paper by M Pont and R Shakeshaft in J. Phys. B: At. Mol. Opt. Phys., 28 L571, and former discussions with M Pont have pointed out to us the importance of integrating the triple differential cross section (TDCS) of double photoionization towards the total cross section σ++. Using our parametrized TDCS, the integrations over the solid angles of the ejected electrons and the final integration over the energy coordinate have been performed, assuming for the last step a flat distribution for the energies of the electrons and avoiding double counting. The resulting integrated cross section σ++(Eexc = 20eV) appears to be too small by a factor of about two when compared to known experimental and theoretical σ++ values, the same conclusion has been derived independently by M Pont, R Shakeshaft, F Maulbetsch and J S Briggs (to appear as a brief report in Phys. Rev. A). In the light of this result, our experimental TDCS values should be revised upwards by a factor of about two, even though we could not find in neither in the individual measurements nor the procedure to derive the absolute TDCS an obvious source for this discrepancy.