Single-Photon Rydberg Excitation and Trap-Loss Spectroscopy of Cold Cesium Atoms in a Magneto-Optical Trap by Using of a 319-nm Ultraviolet Laser System

We demonstrate the single-photon Rydberg excitation of cesium atoms in a magneto-optical trap (MOT). We excite atoms directly from 6S
_1/2
ground state to nP
_3/2
(n = 70-100) Rydberg state with a narrow-linewidth 319-nm ultra-violet laser. The detection of Rydberg states is performed by monitoring the reduction of fluorescence signal of the MOT as partial population on 6S
_1/2
(F = 4) ground state are transferred to Rydberg state. We clearly observe Autler-Townes doublet in the trap-loss spectra due to the cooling lights. Utilizing the large electric polarizibility of Rydberg atoms, we observe Stark splitting in the Autler-Townes doublet induced by background DC electric fields. We investigate the dependence of Stark shift on electric fields by theoretical analysis, and then infer the DC electric field from the measured Stark splitting. We find that there is a 44.8(4) mV/cm DC electric field in the vicinity of the cold ensemble. It indicates that high-lying Rydberg atoms can be used as sensors for DC electric fields.