Rydberg atoms in low-frequency fields : fundamental aspects and applications

Abstract

In this thesis we investigate highly excited atoms, so-called Rydberg atoms, in oscillating fields with frequencies from the megahertz to the terahertz domain. The strong interaction of Rydberg atoms with external fields is used to establish a connection between the ionization of Rydberg atoms by radiofrequency fields and the field ionization process of ground-state atoms by high-power laser pulses, which precedes high-order harmonic generation. This strong interaction leads to asymmetries in the ionization process. Furthermore we propose a photocathode made from Rydberg atoms which can be used to image far-infrared pulses in the THz frequency range. The THz camera presented in this thesis is not restricted to coherent radiation and does not require temporal overlap of two ultrashort pulses, as many THz imaging schemes do. An intricate feature of the interaction of THz pulses and Rydberg atoms which combines weak and strong interactions and coherent excitation is presented and applied to perform far-infrared spectroscopy of a rotational absorption line of water vapor.