Photoassociation of ultracold metastable helium atoms

Photoassociation of metastable He (2³S₁) atoms at ultra low temperatures close to the BEC phase transition is studied, which was achieved previously in an Ioffe-Pritchard magnetic trap and detected optically through absorption imaging of the optical density profile. In the present experiment, the cloud is brought close to the BEC transition by evaporation and then illuminated by laser pulse tunable around the three (2³S₁-2³P_0,1,2) resonance lines at 1083 nm. A subsequent optical density measurement is used to detect any increases in the trap loss rate that may have been caused by the pulse. The experiment is particularly interested in detecting losses due to the production of ultracold molecules by photoassociation (PA), and in finding several weakly bound S-P states that have not previously been detected.