We demonstrate sub-Doppler laser cooling and magneto-optical trapping of the rare earth element Holmium. Atoms are loaded from an atomic beam source and captured in six-beam
σ+−σ− molasses using a strong
J=15/2↔J=17/2 cycling transition at
λ=410.5nm. Due to the small difference in hyperfine splittings and Landé
g-factors in the lower and upper levels of the cooling transition the MOT is self-repumped without additional repump light, and deep sub-Doppler cooling is achieved with the magnetic trap turned on. We measure the leakage out of the cycling transition to metastable states and find a branching ratio
∼10−5 which is adequate for state resolved measurements on hyperfine encoded qubits.
A compact laser cooling system for transportable optical lattice clocks based on cold 171 Yb atoms has been presented. The system size has been reduced by eliminating the first cooling stage and using compact configurations for the main subsystems of the laser cooling system. A Zeeman slower has been modeled and developed, reducing the velocity of atoms from a thermal source to a level sufficient for their direct capture in a second-stage magneto-optical trap, avoiding the first cooling stage. A method for estimating the number of atoms and their temperature in the magneto-optical trap is presented. The performance of the compact laser cooling system with the developed Zeeman slower has been experimentally confirmed: ~10 6 171 Yb atoms with a temperature of ~35 μK have been collected in ~1 s. The achieved parameters allow for loading of ~4000 atoms into the optical lattice.
The possibility of using an atom chip and a diffraction grating to form a compact magneto-optical trap for ytterbium atoms, which can be used to develop compact atomic interferometers and optical clocks based on ultracold atoms, has been studied. An experiment on the laser cooling of the 171Yb and 174Yb isotopes in a first‑stage magneto-optical trap has been carried out to determine initial requirements for the mentioned elements. The design of the atom chip forming a magnetic field gradient up to 60 G/cm has been calculated. The optimal configurations of the diffraction grating that allow forming both the first- and second-stage magneto-optical traps have been evaluated.