H-ATOM IONIZATION BY ELLIPTICALLY POLARIZED MICROWAVE FIELDS - THE OVERLAP CRITERION

The threshold for H-atom ionization by elliptically polarized microwav e fields is discussed within the classical-mechanics framework using t he Chirikov overlap criterion. It is shown that the trends observed in the recent experiment [M. R. W. Bellermann et al. Phys. Rev. Lett. 76 , 892 (1996)] are qualitatively reproduced by the theory; the origin o f the remaining discrepancy is discussed. Increased stability of some orbits with respect to the perturbation due to the elliptically polari zed microwaves has been related to vanishing widths of the correspondi ng resonance islands. Analytic Chirikov overlap prediction is compared with results of numerical simulations.