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

TL;DR

This paper investigates the threshold behavior of field ionization in Rydberg atoms subjected to short single-cycle pulses, revealing a universal inverse scaling with binding energy and identifying a displacement ionization mechanism, along with an ionization window for control.

Contribution

It uncovers the inverse scaling law of ionization thresholds in short pulses, introduces a displacement ionization mechanism, and demonstrates an ionization window for selective Rydberg state manipulation.

Findings

Threshold field scales inversely with binding energy in short pulses.

Displacement ionization is a significant mechanism beyond tunneling and multiphoton ionization.

Existence of an ionization window for controlling Rydberg-state populations.

Abstract

We study the field-ionization threshold behavior when a Rydberg atom is ionized by a short single-cycle pulse field. Both hydrogen and sodium atoms are considered. The required threshold field amplitude is found to scale \emph{inversely} with the binding energy when the pulse duration becomes shorter than the classical Rydberg period, and, thus, more weakly bound electrons require larger fields for ionization. This threshold scaling behavior is confirmed by both 3D classical trajectory Monte Carlo simulations and numerically solving the time-dependent Schr\"{o}dinger equation. More surprisingly, the same scaling behavior in the short pulse limit is also followed by the ionization thresholds for much lower bound states, including the hydrogen ground state. An empirical formula is obtained from a simple model, and the dominant ionization mechanism is identified as a nonzero spatial displacement of the electron. This displacement ionization should be another important mechanism beyond the tunneling ionization and the multiphoton ionization. In addition, an "ionization window" is shown to exist for the ionization of Rydberg states, which may have potential applications to selectively modify and control the Rydberg-state population of atoms and molecules.