ON THE SIMULTANEOUS EJECTION OF SEVERAL ELECTRONS FROM AN ATOM IN A HIGH ELECTROMAGNETIC-FIELD

A basic mean-field theory for the interaction between several bound electrons of an atom and an intense electromagnetic field is presented. From it, we infer that simultaneous ejection of several electrons is to be seen as a zero-order process, i.e. as an independent quasi-particle reaction of dressed single-electron states and that the shell structure of the atom does not dominate the process. Indeed, even inner shell electrons can be ejected in this way, with comparable probability. Our conclusions contrast with those of other authors who have argued that complete shells tend to be blown off or that, as is the case in very low electromagnetic fields where single photon processes dominate, multiple ionization depends for its existence on the magnitude of electron-electron correlations. We estimate the turn-on time of the laser pulse required to observe simultaneous, multiple ionization.