Field-ionization threshold and its induced ionization-window phenomenon for Rydberg atoms in a short single-cycle pulse

摘要

We study the field-ionization threshold behavior when a Rydberg atom isionized by a short single-cycle pulse field. Both hydrogen and sodium atoms areconsidered. The required threshold field amplitude is found to scale\emph{inversely} with the binding energy when the pulse duration becomesshorter than the classical Rydberg period, and, thus, more weakly boundelectrons require larger fields for ionization. This threshold scaling behavioris confirmed by both 3D classical trajectory Monte Carlo simulations andnumerically solving the time-dependent Schr\"{o}dinger equation. Moresurprisingly, the same scaling behavior in the short pulse limit is alsofollowed by the ionization thresholds for much lower bound states, includingthe hydrogen ground state. An empirical formula is obtained from a simplemodel, and the dominant ionization mechanism is identified as a nonzero spatialdisplacement of the electron. This displacement ionization should be anotherimportant mechanism beyond the tunneling ionization and the multiphotonionization. In addition, an "ionization window" is shown to exist for theionization of Rydberg states, which may have potential applications toselectively modify and control the Rydberg-state population of atoms andmolecules.