Subrecoil cooling of ⁶Li atoms by 2S→3P ultraviolet narrow transition

Laser cooling of atoms and molecules is crucial to exhibiting excellent features in the field of low-temperature physics. Cooling ⁶Li atoms to very low temperatures is difficult due to their partially resolved D ₂ line of excited states. Here we report an observation of cooling ⁶Li atom samples to 16 µK with an ultraviolet (UV) laser in a magneto-optical trap, which breaks the Doppler cooling limit and approaches half of the photon-recoil limit. The essential mechanism of cooling results is that the natural linewidth is comparable to the recoil frequency in such a 2S→3P ultraviolet narrow transition. Laser frequency stability is important in the cooling process, and thus, the UV laser was locked to an optical frequency comb referenced to an ultrastable optical cavity. The cooling was numerically simulated to explain the cooling forces. The results can provide an ideal platform in the field of precision measurements and ultracold Fermi gases.