Sub-Doppler cooling of sodium atoms in gray molasses

TL;DR

This paper demonstrates sub-Doppler laser cooling of sodium atoms using gray molasses on the D1 transition, achieving temperatures around 9 μK and high capture efficiency, enhancing cold atom preparation.

Contribution

It introduces a novel application of gray molasses cooling on the D1 line for sodium, achieving lower temperatures and higher efficiency than previous methods.

Findings

Achieved sodium atom temperatures as low as 9 μK.

Capture efficiency exceeds 66%.

No density-dependent heating observed up to 10^{11} cm^{-3}.

Abstract

We report on the realization of sub-Doppler laser cooling of sodium atoms in gray molasses using the D1 optical transition ($3s\, ^2S_{1/2} \rightarrow 3p\, ^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing $3\times10^9$ 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$^{-3}$.