Optimizing a Rydberg Atom-based Terahertz Imaging System

Abstract

We build upon previous work by characterising and optimizing the signal from a Rydberg atom-based terahertz (THz) imaging system, where atoms are excited to a Rydberg state by a three step ladder scheme. These Rydberg atoms provide a THz imaging mechanism via a fluorescence signal, . We implement a Pound-Drever-Hall lock and a digital scanning transfer cavity lock on the Rydberg laser. Both schemes see an improvement in the stability of fluorescence signal over time, to within 3. We characterise the effect of laser parameters on . A pumping scheme consisting of alternating circular polarisations for each step are found to maximise , providing a increase compared to the all-linear configuration. The dependence of on Rydberg laser detuning and THz detuning is also characterised, and splitting due to the AC Stark shift is observed at higher THz powers. Simultaneous resonant excitation of the Rydberg and THz transition is found to maximize . A repump laser is implemented on both the D1 and D2 lines, and found to increase most on the D1 line, by a factor of seven. The effect on of the repump lasers power and detuning is characterised, and a two-photon transition is observed in the D2 line spectrum. A change in spatial intensity distribution of the THz beam is observed under the effect of rotation of a linear polariser, which is theorised to be due to a vector diffraction pattern.