Sub-Doppler cooling with the 1S0-1P1 line in ytterbium

We have studied the temperatures of several neutral Yb isotopes in a magneto-optical trap (MOT) using the ¹S₀-¹P₁ transition at 398.9 nm. We use a compact MOT with a titanium vacuum chamber and a high degree of othogonality between the beams. Minimum temperatures of 170 μK and 80 μK are recorded for ¹⁷¹Yb, and ¹⁷³Yb, respectively, while 0.95 mK is measured for ¹⁷²Yb. By comparison the 1D Doppler cooling temperature limit is 694 μK. The results augur well for future lattice clocks that use Yb. We comment on the significance of sub-Doppler cooling of atoms with ground-state total angular momentum F =1/2, as is the case for ¹⁷¹Yb.