Resonance-induced ionization enhancement and suppression of circular states of the hydrogen atom in strong laser fields

We theoretically investigated the ionization dynamics of a hydrogen atom in circular excited states irradiated by the circularly polarized laser pulses by solving the time-dependent $\mathrm{Schr}\stackrel{\ifmmode \ddot{}\else \"{}\fi{}}{\mathrm{o}}\mathrm{dinger}$ equation. We calculated the ionization yields of the two excited states which are corotating and counter-rotating with respect to the laser fields as a function of the laser frequency. For the corotating excited state, our results show an obvious ionization suppression when the laser frequency is beyond the one-photon ionization threshold, and it is followed by a strong ionization enhancement when the laser frequency further increases. These ionization suppressions and enhancements are absent for the counter-rotating excited state. By tracing the ionization process, we found that resonance between the initial state and a lower-energy state occurs at the frequency of the ionization enhancement. Ionization from this lower-energy state is responsible for this ionization enhancement. At the frequency of ionization suppression, Rabi oscillation between the initial and the lower-energy state occurs, which prevents further ionization and thus suppresses the final ionization yield.