Kinetic Energies in the Direct Double Photoionization of Helium and the Electron-Electron Correlation

We present a simple model describing kinetic energy probability distributions of outgoing electrons in the direct double photoionization of helium. The model applies to photons of energy greater than the binding energy of the atom and to radiation intensities extending from perturbation regime to the strong-field one. It appears that the shape of probability distribution is mainly determined by the electron-electron correlation in their final state. For nonperturbative intensities the distribution depends strongly on polarization of incident radiation.