Inverted-ladder-type optical excitation of potassium Rydberg states with hot and cold ensembles

Abstract

We present experimental results on the sub-Doppler Rydberg spectroscopy of potassium in a hot cell and cold atoms, using two counterpropagating laser beams of 405 and 980 nm as an inverted ladder-type excitation configuration (4S 1/2-5P 3/2-nS 1/2 and nD 3/2,5/2). Such an inverted ladder-type scheme is predicted to be without the sub-Doppler electromagnetically induced transparency feature in a thermal ensemble under the weak-probe approximation. Instead, we utilize a strong probe field and successfully observe a transparency window with a width narrower than 50 MHz. Our all-order numerical simulation is in satisfactory agreement with the experimental results. This narrow linewidth allows us to measure the energy levels of the Rydberg levels from n = 20-70 with improved accuracy. The deduced ionization energy agrees with the previous measurements. Furthermore, the two-photon Rydberg excitation scheme was applied to the cold ensembles to study the ground-state atoms population decrease in the magneto-optical trap for various Rydberg states. Our experimental observations suggested two distinct regimes of the trap losses under different probe detuning conditions. While the far off-resonance case (p 0) can be described by the picture of dressed atom, the on-resonance case (p ∼ 0) reveals more interesting results. The higher Rydberg states suffer larger trap loss. Besides, even with similar level energies, the excitation to nD states result in faster escape of the ground-state atom from trap than nearby nS states.

EIT spectroscopy of high-lying Rydberg states in $^{39}K$

“…Compared to other experimentally measured energies of 39 K Rydberg states (Table I), ours agree with recent results from Ref. [26] within uncertainties, except for 68S.…”

“…Notwithstanding this, our ionization energies and δ 0 agree with results derived using similar methods in Refs. [23,25,26,38].…”

“…High-lying Rydberg states with n ∼ 60 − 90 in 39 K would be particularly relevant to future axion searches in this mass range. However, only a few of the Rydberg states with n > 50 have been identified in previous spectroscopy studies [23][24][25][26]. Therefore, we study the energy spectrum of high-lying Rydberg states with n ∼ 50 − 90 using an all-optical detection based on electromagnetically induced transparency (EIT) [27][28][29].…”

Advancing Rydberg atom-based axion detection

“…Therefore, creating the Rydberg states in an atomic beam requires finding the energy difference between the 39 K ground state and the desired Rydberg state, and then finding the laser frequency that corresponds to that energy difference. However, the literature was sparse in identifying Rydberg states in 39 K with n > 50, [43][44][45][46] so we needed to find the energy spectrum of n ∼ 50 − 90 ourselves. Additionally, simulations show that the approximate wavelength required to get 39 K to these Rydberg levels is 286 nm, 47 which is in the ultraviolet range.…”