Auto-ionization and stochastic diffusion of Rydberg electrons in fluctuating laser fields

The influence of laser fluctuations on the excitation of auto-ionizing Rydberg states close to an ionization threshold is investigated. Based on quantum defect theory a theoretical framework is developed within which all threshold phenomena originating from the infinitely many Rydberg states converging towards the ionization threshold as well as the stochastic influence of the exciting laser field can be described conveniently. It is demonstrated that the competition between the coherent process of auto-ionization and the incoherent processes induced by the fluctuating laser field leads to a variety of novel phenomena.