SUB-DOPPLER LASER COOLING OF LITHIUM ATOMS IN A GRAY OPTICAL MOLASSES

Abstract

Alkali-metal atoms are prime candidates for studies of degenerate quantum gases and laser cooling and trapping of these elements to the Doppler limit is conventionally done on the D2 transition. However, typical sub-Doppler cooling techniques are not effective for lithium because of this species' unresolved hyperfine structure in the excited state. In this research work, a gray molasses operating on the D1 atomic transition is employed to efficiently cool a cloud of lithium-6 atoms from 380 to 32 μK in 2.5 ms. From a compressed magneto-optical trap (MOT), 2.8 ∗ 10⁸ atoms are captured in the low-intensity molasses. The peak and phase-space densities observed are compared to previously obtained results for gray molasses experiments, and to those achieved in a different method employed in our group that uses a two-stage magneto-optical trap. Due to a reduction in the peak density after the molasses phase, an attempt to transfer of the atoms into an optical dipole trap was so far not efficient. A discussion is given, and suggestions are put forward to improve these results.