Structure in the angular dependence of optical suppression of photoassociative ionization collisions within an optically cooled and collimated sodiumatom beam

We report measurements of the angular distribution of optical suppression i n photoassociative ionization collisions taking place within a bright, slow Na atom beam. At a collision "temperature" (T = E-kin/k(B)) Of about 5 mK we observe rich structure in the suppression measure as a function of the a ngle between the atom-beam axis and the polarization axis of the suppressor light beam. This structure cannot be explained by the superposition of ind ividual partial-wave contributions to the suppression measure, and we propo se a partial-wave interference phenomenon to account for it.