Sub-Doppler Laser Cooling of Thulium Atoms in a Magneto-optical Trap

TL;DR

This paper demonstrates effective sub-Doppler laser cooling of thulium atoms in a magneto-optical trap, achieving temperatures well below the Doppler limit without dedicated molasses cooling, due to near-degenerate Landé-g factors.

Contribution

It provides the first experimental observation of sub-Doppler cooling in thulium atoms at 410.6 nm, leveraging near-degenerate Landé-g factors for enhanced cooling efficiency.

Findings

Achieved atom cloud temperature of 25(5) μK

Observed cooling below the Doppler limit of 240 μK

Demonstrated high-efficiency sub-Doppler cooling in thulium

Abstract

We have experimentally studied sub-Doppler laser cooling in a magneto-optical trap for thulium atoms working at the wavelength of 410.6\,nm. Without any dedicated molasses period of sub-Doppler cooling, the cloud of $3\times 10^6$ atoms at the temperature of 25(5)\,$\mu$K was observed. The measured temperature is significantly lower than the Doppler limit of 240$\mu$K for the cooling transition at 410.6\,nm. High efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Land\'e-$g$ factors of the lower $4f^{13}6s^{2}\, (J\,=\,{7}/{2})$ and the upper $4f^{12}5d_{3/2}6s^{2}\, (J\,=\,{9}/{2})$ cooling levels.}