Massively parallel ionization of extended atomic systems.

Massively parallel ionization of many atoms in a cluster or biomolecule is identified as a new phenomenon of light-matter interaction which becomes feasible through short and intense FEL pulses. Almost simultaneously emitted from the illuminated target the photo-electrons can have such a high density that they interact substantially even after photoionization. This interaction results in a characteristic electron spectrum which can be interpreted as a convolution of a mean-field electron dynamics and binary electron-electron collisions. We demonstrate that this universal spectrum can be obtained analytically by summing synthetic two-body Coulomb collision events. Moreover, we propose an experiment with hydrogen clusters to observe massively parallel ionization.