Sub-Doppler magneto-optical trap for calcium

We explore an efficient method for preparing large samples of ultracold calcium atoms. An optimized conventional (Doppler-limited) magneto-optical trap collects atoms from a Zeeman cooled atomic beam using a strong dipole transition within the singlet system. This transition is not completely closed thus yielding an intense flux of atoms into the metastable triplet state 3P2. A second magneto-optical trap sharing the same magnetic-field gradient is superimposed which captures and further cools the metastables using the narrow-band infrared transition 3P2→3D3. In our present experiment we were able to prepare 3x108 atoms at temperatures below 20 microkelvin within 250 ms. Minor technical improvements of our setup promise to yield above 1010 atoms at submicrokelvin temperatures within 1 s