Magneto-optical trap for metastable helium at 389 nm

We have constructed a magneto-optical trap (MOT) for metastable triplet helium atoms utilizing the 2 S-3(1)-->3 P-3(2) line at 389 nm as the trapping and cooling transition. The far-red-detuned MOT (detuning Delta=-41 MHz) typically contains few times 10(7) atoms at a relatively high (similar to10(9) cm(-3)) density, which is a consequence of the large momentum transfer per photon at 389 nm and a small two-body loss rate coefficient (2x10(-10) cm(3)/s<beta<1.0x10(-9) cm(3)/s). The two-body loss rate is more than five times smaller than in a MOT on the commonly used 2 S-3(1)-->2 P-3(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.