Closed-orbit theory for photodetachment in a time-dependent electric field

TL;DR

This paper extends closed-orbit theory to analyze photodetachment of negative ions in a time-dependent electric field, specifically a terahertz pulse, revealing how the detachment rate oscillates with pulse strength and orbit geometry.

Contribution

The authors develop a generalized closed-orbit theory for time-dependent fields and identify classical orbit types influencing photodetachment rates in strong terahertz pulses.

Findings

Photodetachment rate remains unaffected by weak terahertz fields.

Strong terahertz pulses induce complex oscillations in the detachment rate.

In-phase and antiphase oscillations depend on orbit geometry.

Abstract

The standard closed-orbit theory is extended for the photodetachment of negative ions in a time-dependent electric field. The time-dependent photodetachment rate is specifically studied in the presence of a single-cycle terahertz pulse, based on exact quantum simulations and semiclassical analysis. We find that the photodetachment rate is unaffected by a weak terahertz field, but oscillates complicatedly when the terahertz pulse gets strong enough. Three types of closed classical orbits are identified for the photoelectron motion in a strong single-cycle terahertz pulse, and their connections with the oscillatory photodetachment rate are established quantitatively by generalizing the standard closed-orbit theory to a time-dependent form. By comparing the negative hydrogen and fluorine ions, both the in-phase and antiphase oscillations can be observed, depending on a simple geometry of the contributed closed classical orbits. On account of its generality, the presented theory provides an intuitive understanding from a time-dependent viewpoint for the photodetachment dynamics driven by an external electric field oscillating at low frequency.