Bidirectionally kicked Rydberg atoms: Population trapping near the continuum

The behavior of high-n Rydberg atoms subject to a periodic sequence of short half-cycle pulses (HCPs) that alternate in sign is reexamined. Each HCP delivers an impulsive momentum transfer or “kick” to the electron and the net average field it experiences is zero. The data show that the excited electron energy distribution initially moves toward the continuum, i.e., toward states of higher n, but then becomes transiently trapped near the edge of the continuum leading to sizable overall survival probabilities. The physical mechanisms responsible for this are discussed with the aid of classical trajectory Monte Carlo simulations.