We descrbe a new method for measuring excited-state collisions between optically trapped atoms. With this method, trap-loss collision rates are deduced from the loading behavior of clouds of trapped atoms in the regime where radiation trapping limits the atom density. Our measurements indicate that ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ trap-loss collisions occur at significantly smaller rates than expected both from previous work on Cs and from recent models. In addition, the dependence of the trap-loss collisions on the frequency of the light used to excite the atom pairs is also different from that of Cs, suggesting that assumptions about the dynamics in these models need modification.

• Received 19 May 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.753