Sub-Doppler cooling of ytterbium with the ¹S₀-¹P₁ transition including ¹⁷¹Yb (I=1/2)

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We report on the sub-Doppler laser cooling of neutral ¹⁷¹Yb and ¹⁷³Yb in a magneto-optical trap using the ¹S₀-¹P₁ transition at 398.9nm. We use two independent means to estimate the temperature of the atomic cloud for several of the Yb isotopes. The two methods of MOT-cloud-imaging and release-and-recapture show consistency with one another. Temperatures below 400μK and 200μK are recorded for ¹⁷¹Yb and ¹⁷³Yb, respectively, while 1mK is measured for both ¹⁷²Yb and ¹⁷⁴Yb. By comparison, the associated 1D Doppler cooling temperature limit is 694μK. The sub-Doppler cooling of the I=1/2 ¹⁷¹Yb isotope in a σ⁺-σ⁻ light-field trap adds further evidence that the Sisyphus cooling mechanism is occurring in such 3D magneto-optical traps.