Abstract
We present experimental results on the sub-Doppler Rydberg spectroscopy of potassium in a hot cell and cold atoms, performed with two counter-propagating laser beams of 405 nm and 980 nm in the inverted ladder-type system (4S1/2-5P3/2-nS1/2 and nD3/2;5/2). Such an inverted ladder-type scheme is predicted to be without sub-Doppler electromagnetically induced transparency (EIT) feature in a thermal ensemble under the weak-probe approximation. Instead, we utilized a strong probe field and successfully observed 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 MOT 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 (\delta p>>0) can be described by the picture of dressed atom, the on-resonance case (\delta 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.
Highlights
A Rydberg atom, which is an excited atom with one or more electrons in a high principal quantum number (n) state has gained growing interest recently because of its extremely large polarizability
With a potassium hot vapor cell, we successfully demonstrate a sub-Doppler EIT spectroscopy using two-step excitation in an inverted ladder-type scheme
We develop a theoretical model using optical Bloch equations without the weak probe approximation, which is in an excellent agreement with our experimental results
Summary
A Rydberg atom, which is an excited atom with one or more electrons in a high principal quantum number (n) state has gained growing interest recently because of its extremely large polarizability. More comprehensively, we experimentally studied the optical excitation of K Rydberg states using both hot and cold atoms, together with a numerical simulation comparison. Towards the heteronuclear Rydberg atoms interaction applications, such a high-power laser acts as an optical dipole trap for the ultracold atomic ensembles of K and Rb. Despite the inverted ladder-type scheme, in hot atomic ensembles there was known to be the lack of a sub-Doppler feature, such as EIT, in the weak probe approximation using a simple three-level model [27]. We employed the steady-state approach to show that the trap loss, induced by the interaction between the ground-state and Rydberg atoms, depends on the principle quantum number n, and the orbit angular momentum l
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