Abstract-Probing double Rydberg wave packets in a helium atom with fast single-cycle pulses

Xiao Wang and F. Robicheaux

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.96.043409

Fully quantum and classical calculations on a helium atom with two excited, radially localized Rydberg wave packets are performed. The differences between classical and quantum methods are compared for a wide range of principal quantum numbers to study the validity of the classical method for low-lying states. The effects of fast terahertz single-cycle pulses on an atomic system with one or two Rydberg wave packets are also studied using classical equations of motion. These results suggest that single-cycle pulses can be used as time-resolved probes to detect motion of the wave packets and to investigate autoionization properties.

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

B. C. Yang and F. Robicheaux

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.053413

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.

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Abstract-Temporal interferences driven by a single-cycle terahertz pulse in the photodetachment dynamics of negative ions

B. C. Yang and F. Robicheaux

http://journals.aps.org/pra/accepted/ed07dNdfYf519e16d2a313c51b13ef2e1db7dc640

We present theory and calculations of a real-time-domain interferometry for the photodetachment dynamics of negative ions in the presence of a single-cycle terahertz pulse. The photoelectron can follow two or more classical trajectories to arrive at a detector \emph{simultaneously} allowing the electron waves to interfere quantum mechanically. Both the inphase and antiphase oscillations can be observed in the photoelectron interferences from negative hydrogen and fluorine ions depending on the pulse strength and the observing angle. Especially, a temporal-caustic bifurcation is observed when the detecting angle is not in the line with the pulse polarization direction. Similar interferences and bifurcations are also expected in the angle-resolved energy spectrum, as a result of its approximate equivalence with the time-dependent electron flux at large distances.