Collision self-ionization and self-excitation of a single atom in superbright pumping laser field

The process of self-ionization and self-excitation of atoms of rarefied gases in superbright laser fields (with intensity greater than or equal to 10 to the 17 W/cm-squared) is considered. In rarefied gases the ionization and excitation process is not a single one. The electrons generated from the ionization of the atom beyond the threshold ionization level remain in the neighborhood of the atom and oscillate near their own particular atom. If one considers that this atom is not an attracting point, the free electrons in a certain point in space will appear at that point with the same velocity after one oscillation period. Because the electron has low velocity at the moment it becomes a free electron, such an electron cannot produce either ionization or excitation at this attracting point. This study considers whether the situation is changed when an attracting center does exist. It is found that multiphoton semiclassical ionization (and excitation) prevail in the case of red and IR laser pumping radiation with circular polarization and high field strength. For lasers with linearly polarized blue, violet, and UV radiation, collision processes are the predominant mechanisms at lower intensities. 7 refs