Deep Laser Cooling of Thulium Atoms to Sub-$\mu$K Temperatures in Magneto-Optical Trap

Deep laser cooling of atoms, ions, and molecules facilitates the study of fundamental physics as well as applied research. In this work, we report on the narrow-line laser cooling of thulium atoms at the wavelength of $506.2\text{nm}$ with the natural linewidth of $7.8\text{kHz}$, which widens the limits of atomic cloud parameters control. Temperatures of about $400\text{nK}$, phase-space density of up to $3.5\times {10}^{-4}$ and $2\times {10}^6$ number of trapped atoms were achieved. We have also demonstrated formation of double cloud structure in an optical lattice by adjusting parameters of the $506.2\text{nm}$ magneto-optical trap. These results can be used to improve experiments with BEC, atomic interferometers, and optical clocks.