Development of a continuous-wave, deep-ultraviolet, and single-frequency coherent light source-challenges toward laser cooling of silicon

Laser cooling techniques of silicon may be a powerful tool to create a new silicon road map. In the first step, to realize the laser cooling of neutral silicon atoms highly efficient frequency conversions are conducted to obtain a deep-ultraviolet single-mode coherent light using two-stage external cavities. The 154-mW power at around 252 nm is obtained with a conversion efficiency of more than 8% by doubly resonant sum-frequency mixing of 373-nm light from the first-stage conversion and 780-nm light from a single-mode Ti:sapphire laser. This paper reviews a series of challenges for taking possession of the spatial design of nuclear spins of the family of stable isotopes with laser cooling of silicon.