Discrete-time picture for multiphoton microwave spectroscopy

Abstract

The time evolution of atomic and molecular systems driven by periodic external fields is reformulated to combine Floquet's theorem with time-dependent representations of the atomic degrees of freedom. This approach increases the flexibility of Floquet calculations of multiphoton processes in strong radiation fields, particularly at low frequencies, by incorporating adiabatic states into the basis. The depopulation of Rydberg states of He and Na in strong microwave fields illustrates the utility of the method. In particular, a study of the depopulation of the 11s state of Na in an oscillatory field reveals a strong correspondence between dc-field Stark maps and quasienergy spectra and predicts a resonance feature associated with Landau-Zener transitions between dc Stark levels.