Frequency-tunable narrow-linewidth watt-level 318-nm UV laser system and single-step Rydberg excitation of cesium cold atoms

We used narrow-linewidth 1560.492-nm and 1076.956-nm single-frequency MOPA fiber lasers to produce 637.2-nm red laser efficiently via single-pass Sum-Frequency Generation (SFG) with PPLN crystal. The cavity-enhanced Second-Harmonic Generation (SHG) with BBO crystal was utilized to produce the frequency-tunable narrow-linewidth watt-level 318.6-nm UV laser. Red Pitaya modules based on FPGA were employed to lock the SHG cavity with BBO crystal to 637.2-nm red laser via PDH locking scheme, and also lock the 1560.492-nm MOPA fiber laser to Rubidium-87 D2 transition via single-pass PPLN frequency doubling to 780.246 nm and Rubidium polarization spectroscopy. We achieved 318.6-nm UV laser with more than 2 Watts output and its linewidth is < 10 kHz. Using the 318.6-nm UV laser system, we have realized the single-step Rydberg excitation from the ground state 6S1/2 to the Rydberg state nP3/2 (n = 70~100) of cesium atoms in hot atomic vapor cell and laser cooled and trapped in a MOT. The background DC electric fields were measured experimentally via cold Rydberg atoms’ Stark effect. To avoid random localized electric fields which come from the self-ionization of Rydberg atoms, the Rydberg weakly-dressed ground state of cold cesium atoms will be prepared via 318.6-nm UV laser and will be employed to detect weak DC electric fields via Ramsey interferometer. Refs: [1] JOSAB, 33 (2016) p.2020; [2] Opt. Express, 25 (2017) p.22510; [3] IEEE J. Sel. Topics Quant. Electr., 26 (2020) 1600106; [4] J. Quant. Opt., 31 (2025) 011001 (in Chinese); [5] Opt. Express, 33 (2025) p.7081