ULTRACOLD COLLISIONS AND OPTICAL SHIELDING IN METASTABLE XENON

Collisions between laser-cooled metastable xenon atoms in the presence of laser fields provide a good experimental test for ultracold collis ion theories as the observed ionization can be directly linked to the atomic binary collisions. Hyperfine structure is not present for the e ven isotopes Xe-132 and Xe-136, which simplifies the theoretical work. We present our results and show how these and the results presented i n Walhout et al. [Phys. Rev. Lett, 74, 605 (1995)] can be interpreted with suitably adapted two-state models. Our approach suggests one poss ibility why the strong shielding of collisions predicted by the simple two-state model of Suominen et al. [Phys. Rev. A 51, 1446 (1995)] has not been achieved in the xenon experiment.