Microwave ''ionization'' of excited hydrogen atoms: Frequency dependence in a resonance zone

In the microwave ''ionization'' of excited 3d H atoms by a linearly polarized field, we observe experimentally for the first time a fine-scale frequency dependence that is suppressed when relatively weak broad-band noise is added to the driving field. We use 1d classical calculations, 1d quantal calculations and Husimi wave function distributions to give a semiclassical explanation for the delicate behavior.