We study the role of classical resonances in quantum systems subjected to a periodic external force. It is demonstrated that classical invariant vortex tubes determine the structure of Floquet states ‘‘captured’’ by resonances in the classical phase space. In addition, resonance quantum numbers are introduced. The analysis of simple model calculations leads to a qualitative description of nonperturbative phenomena relevant for the interaction of atoms or molecules with strong, short laser pulses.     «

We study the role of classical resonances in quantum systems subjected to a periodic external force. It is demonstrated that classical invariant vortex tubes determine the structure of Floquet states ‘‘captured’’ by resonances in the classical phase space. In addition, resonance quantum numbers are introduced. The analysis of simple model calculations leads to a qualitative description of nonperturbative phenomena relevant for the interaction of atoms or molecules with strong, short laser pulses...     »