Pulsed Rydberg four-wave mixing with motion-induced dephasing in a thermal vapor

TL;DR

This paper demonstrates time-resolved pulsed four-wave mixing in thermal Rubidium vapor involving Rydberg states, revealing motion-induced dephasing, revivals of signals, and the impact of Doppler class selectivity, supported by numerical simulations.

Contribution

It introduces a resonant FWM scheme in thermal vapor showing richer temporal dynamics and motion-induced revivals, with detailed modeling of Doppler effects.

Findings

FWM signals with dephasing times up to 7 ns

Observation of signal revivals shortly after pulse termination

Numerical simulations qualitatively match experimental data

Abstract

We report on time-resolved pulsed four-wave mixing (FWM) signals in a thermal Rubidium vapor involving a Rydberg state. We observe FWM signals with dephasing times up to 7 ns, strongly dependent on the excitation bandwidth to the Rydberg state. The excitation to the Rydberg state is driven by a pulsed two-photon transition on ns time scales. Combined with a third cw de-excitation laser, a strongly directional and collective emission is generated according to a combination of the phase matching effect and averaging over Doppler classes. In contrast to a previous report [1] using off-resonant FWM, at a resonant FWM scheme we observe additional revivals of the signal shortly after the incident pulse has ended. We infer that this is a revival of motion-induced constructive interference between the coherent emissions of the thermal atoms. The resonant FWM scheme reveals a richer temporal structure of the signals, compared to similar, but off-resonant excitation schemes. A simple explanation lies in the selectivity of Doppler classes. Our numerical simulations based on a four-level model including a whole Doppler ensemble can qualitatively describe the data.