Time dependent screening in the photoionization of doubly excited two-electron systems

We have investigated the two-electron dynamics of asymmetric doubly highly excited high angular momentum states in Sr interacting with a laser field. Even down to modest laser intensities the dominant fragmentation process is the photoionization of the inner electron. Analysis of the final ionic state reveals that the near-threshold ionization process is compatible with a time dependent screening of the nuclear charge on a time scale comparable to the orbit time of the outer electron. This is evidence of long-range dipolar correlation forces during the ionization process.