Development of a high-power deep-ultraviolet continuous-wave coherent light source for laser cooling of silicon atoms

We developed a robust, high-power, tunable, CW, single-mode, and deep-UV coherent light source by two-stage highly efficient frequency conversions with external cavities We obtained the second harmonic power of 500 mW, corresponding to the generation of more than 520 mW in the cavity. This result shows more than 40% of the total conversion efficiency from the input power to the generated power. In the second bow-tie-type external cavity the obtained 373 nm light and 780 nm light provided by a diode laser are doubly resonantly sum-frequency-mixed in the other external cavity to generate the 252 nm light. The power of 252 nm radiation of 50 mW was obtained out of the cavity when the power of 780 nm radiation was 380 mW. The input power of the 373 nm light was 480 mW under this condition. The generated intracavity power was estimated to be more than 60 mW. Then, the enhancement factors were measured as 34 and 92 for 373 nm and 780 nm light, respectively. when the wavelength of the LD was tuned from 767 nm to 785 nm and the angle of the crystal was well adjusted to satisfy the phase-matching condition, the deep-UV light was tuned from 251 nm to 253 nm with the average power of 48 mW. This tuning range sufficiently covers the cooling transitions of silicon isotopes