SPECIAL AMO SEMINAR<br>Production of Extremely High-Lying States as a Byproduct of Microwave Ionization of Rydberg Atoms

In this talk, I will cover a recently observed phenomenon closely related to the ionization of Rydberg atoms by electric fields of microwave frequency. When Rydberg states of Li or Na atoms are exposed to a multi-cycle microwave pulse with frequency in a region of 17 – 80 GHz, a substantial fraction of population remains bound in the form of very high states with n > 300. Despite being very weakly bound, these states survive the microwave field but are easily ionized by static fields with amplitudes lower by more than three orders of magnitude. The production of the high-lying stable states may be attributed to a recombination process in the microwave field or a multiphoton excitation to the continuum and is related to recent experiments with ultra-intense attosecond laser pulses and an observation of low energy electrons in ATI. I will present experimental results showing that the production and survival of these states is a general feature of microwave ionization and try to uncover a mechanism responsible for it.