The photodouble ionisation of helium and heavier rare gases

Recent progress in the understanding of the photodouble ionisation process in He and a new set of measurements in Ar are reported. In the case of He we discuss a method which allows to extract the complex amplitudes of the triple differential cross section (TDCS) and their relative phase from the experimental data. This method provides a compact way to compare theory and experiment and does not rely on any assumption on the energy and angular dependence of the TDCS. The results of the TDCS of the Ar2+3p4(3Pe) state measured at 20 eV excess energy in equal energy sharing conditions are presented. The data of the present experiment and previous ones of the He2+(1Se) state in the same kinematic have been represented by an 'exact' parameterisation of the triple differential cross section (Malegat et al 1997 J. Phys. B: At. Mol. Opt. Phys. 30 251).