Study For The Cooling Laser Of The ¹⁹⁹Hg⁺ Optical Frequency Standard

The reference of optical frequency standards is higher at the 4-5 levels than microwave frequency standards. Being of the superiority, optical frequency standards will be hopeful to become the next generation of frequency standards.The energy level structure of ¹⁹⁹Hg⁺ suggests that ¹⁹⁹Hg⁺ optical frequency standards require two 194 nm ultraviolet lasers with the frequency deviation of 47.2GHz to be the cooling lasers. Since this mature commercial product is not exists, we need to make it by ourselves. The main work of this thesis is production of the 194 nm deep ultra-violet CW lasers in experiment. Due to the opacity to deep ultra-violet lasers with wavelength below 200 nm of the majority of nonlinear crystals, we product 194 nm lasers by the sum frequency of 718 nm laser and 266 nm laser in BBO crystal. This thesis introduces the theoretical analysis and experiment research of the whole process, which includes the following aspects:1. Design and realization of the Compact SHG system. The impact of the fundamental wave's waist shape in crystal to conversion efficiency is analysized. Using the elliptical focusing wave, we obtain high power 266 nm radiation output by adopting a Hansch-Couillaud locking method. 340 m W 266 nm radiation output is obtained when 2W fundamental wave input. The SHG conversion efficiency reaches 17%. The beam distortion due to walk-off effect is improved by the cylindrical lens. As a result, the beam quality becomes much better.2. We obtain the 194 nm laser by summing the 718 nm laser and the 266 nm laser. The output of 194 nm laser meets the need of ¹⁹⁹Hg⁺ optical frequency standards. More than 1m W 194 nm deep ultra-violet CW output is obtained when 300 m W 266 nm and 800 m W 718 nm input.3. Integrated experimental system which to product two 194 nm waves with 47.2GHz frequency deviation is constructed. It is used to detect fluorescence signal of the trapped Hg ions.4. Structure and operating principle of the locking circuit are introduced. The time from unlocking to relocking is less than 2 second. Continuous locking time reaches 30 minutes for one-time.