H-atom ionization by elliptically polarized microwave fields: Three-dimensional analysis

The classical analysis of H-atom ionization by elliptically polarized microwave fields is performed for a realistic three-dimensional model of an atom. As a limiting situation the circular polarization case is discussed in detail too. The sensitivity of initial electronic orbits of different orientation to microwave perturbation is studied analytically using the Chirikov overlap criterion. Generally the orbits lying in the polarization plane are most vulnerable to microwave perturbation, although important exceptions from this rule of thumb are found. In particular a class of orbits is found that is unusually stable against the perturbation. This behavior is linked to vanishing widths of the corresponding resonance islands within the first-order perturbation theory. The results of a recent experiment [Bellerman et al., Phys. Rev. Lett. 76, 892 (1996)] are qualitatively reproduced by the theory.