Optical collisions of ultracold alkali atoms

We develop an approach for describing ultracold-atom collisions in a laser field, incorporating laser excitation during the collision as well as the subsequent spontaneous emission. To include the latter is essential, because the duration of the collisions is longer than the excited-state lifetime. Existing treatments are based on a density matrix description of internal states, combined with a classical description of translational motion. With the presently achieved temperatures of a few times the recoil temperature in mind, we investigate possibilities to describe also the atomic motion during the collision quantummechanically. In our contribution we present preliminary results for an approach in which only one dressed-state manifold is included in the description. The loss of flux from this original manifold due to spontaneous emission is taken into account, but not its recycling through further laser excitation