Power dependent loss from a ytterbium magneto-optic trap

Summary form only given. Magneto-optic trapping of Yb is facilitated by use of a strong transition of the 555.6 nm (6s/sup 2/)/sup 1/S/sub 0/-(6s6p)/sup 3/P/sub 1/ inter-combination line. This line is not radiatively closed, however, and some the decay channels terminate in metastable states, resulting in magneto-optic trapping (MOT) lifetimes that depend on the fraction of atoms in the upper level of the cooling transition. We describe a quantitative study of trap lifetime versus trapping beam power that complements earlier predictions and qualitative experimental results. Our work constitutes the first use of MOT loss rates to measure an excited-state radiative branching ratio.