Sub-Doppler cooling of sodium atoms in gray molasses

Abstract

We report on the realization of sub-Doppler laser cooling of sodium atoms in gray molasses using the D1 optical transition ($3s{}^2{S}_{1/2}\to 3p{}^2{P}_{1/2}$) at 589.8 nm. The technique is applied to samples containing $3\times 10^9$ atoms, previously cooled to 350 $\mu$K in a magneto-optical trap, and it leads to temperatures as low as 9 $\mu$K and phase-space densities in the range of $10^{-4}$. The capture efficiency of the gray molasses is larger than 2/3, and we observe no density-dependent heating for densities up to $10^{11}$ cm${}^{-3}$.

6 pages, 4 figures