We demonstrate microwave-to-optical conversion using six-wave mixing in 87 Rb atoms where the microwave field couples to two atomic Rydberg states, and propagates collinearly with the converted optical field. We achieve a photon conversion efficiency of ∼ 5% in the linear regime of the converter. In addition, we theoretically investigate all-resonant six-wave mixing and outline a realistic experimental scheme for reaching efficiencies greater than 60%.
Starting from weakly bound Feshbach molecules, we demonstrate a two-photon pathway to the dipolar ground state of bi-alkali molecules that involves only singlet-to-singlet optical transitions. This pathway eliminates the search for a suitable intermediate state with sufficient singlet-triplet mixing and the exploration of its hyperfine structure, as is typical for pathways starting from triplet dominated Feshbach molecules. By selecting a Feshbach state with a stretched singlet hyperfine component and controlling the polarization of the excitation laser, we assure coupling to only a single hyperfine component of the A 1 Σ + excited potential, even if the hyperfine structure is not resolved. Similarly, we address a stretched hyperfine component of the X 1 Σ + rovibrational ground state, and therefore an ideal three level system is established. We demonstrate this pathway with 6 Li 40 K molecules. By exploring deeply bound states of the A 1 Σ + potential, we are able to obtain large and balanced Rabi frequencies for both transitions. This method can be applied to other molecular species.
We use two continuous-wave (CW) laser beams of 780 nm and 515 nm to optically drive 85 Rb atoms in a heated vapor cell to a low-lying Rydberg state 10D 5/2 . We observe a collimated ultraviolet (UV) beam at 311 nm, corresponding to the transition frequency from the 11P 3/2 state to the 5S 1/2 state. This indicates the presence of a coherent four-wave mixing process, built up by two input laser fields as well as a terahertz (THz) radiation of 3.28 THz that is generated by amplified spontaneous emission between the 10D 5/2 and the 11P 3/2 states. We characterize the 311 nm UV light generation and its dependence on various physical parameters. This scheme could open up a new possibility for generating narrow-band THz waves as well as deep UV radiation.
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