We have constructed a magneto-optical trap (MOT) for metastable triplet helium atoms utilizing the $2{}^{3}{S}_{1}\ensuremath{\rightarrow}3{}^{3}{P}_{2}$ line at 389 nm as the trapping and cooling transition. The far-red-detuned MOT (detuning $\ensuremath{\Delta}=\ensuremath{-}41\mathrm{MHz})$ typically contains few times
107 atoms at a relatively high $(\ensuremath{\sim}{10}^{9}{\mathrm{cm}}^{\ensuremath{-}3})$ density, which is a consequence of the large momentum transfer per photon at 389 nm and a small two-body loss rate coefficient $(2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}{\mathrm{cm}}^{3}/\mathrm{s}<\ensuremath{\beta}<1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{\mathrm{cm}}^{3}/\mathrm{s}).$ The two-body loss rate is more than five times smaller than in a MOT on the commonly used $2{}^{3}{S}_{1}\ensuremath{\rightarrow}2{}^{3}{P}_{2}$ line at 1083 nm. Furthermore, laser cooling at 389 nm results in temperatures somewhat lower than those achieved using 1083 nm. The 389-nm MOT exhibits small losses due to two-photon ionization, which have been investigated as well.
We report the measurement of one-body loss rates for magnetically trapped metastable europium atoms and the study of their loss mechanism. The loss of atoms observed in a magneto-optical trap is not fully understood because of the indivisibility of the loss regarding optical pumpings due to the presence of cooling laser beams. We magnetically trap the atoms by directly loading from the magneto-optical trap and observe almost identical one-body loss rates of approximately
2.6s−1 for two isotopes:
151Eu and
153Eu. Our rate-equation-based model, combined with loss rate measurements carried out with repumpers, shows that blackbody radiation at room temperature drives E1 transitions and induces the observed losses.