Excitation and ionization of hydrogen atoms by ultra-intense fields

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Abstract
The Volkov wavepacket is used to trace the evolution of a ground-state hydrogen atom in an ultra-intense field, where the peak electric field strength is larger than the mean Coulomb binding field. We find the probabilities for excitation and ionization by projecting the time-dependent wavefunction onto the field-free atomic states. The ground-state atom is drastically shaken up into highly excited Rydberg states and continuum states within a very short time. Results are given for linearly and circularly polarized oscillating fields and for static fields. The dominant mechanism is field excitation and emission as a result of the instantaneous binding potential being suppressed below all bound-state energy levels. Our results are quite different from those of several other authors, some of whom claim that bound-state stabilization occurs in the high-field limit. We see no stabilization and we comment on possible reasons for the diverse results.