Ionization of atoms in intense laser fields. Strong mixing of auto- and photoionizations

Photoelectron spectra of an atom with an autoionizing state in intense laser fields are investigated theoretically. In intense fields, photoelectron spectra are found to have a profile totally different from that in weak fields. A “phase transition” is found to take place at a critical laser intensity and the spectral profile changes drastically at this critical point. This phenomenon originates from mixing of auto- and photoionizations in intense laser fields.