NON-HERMITIAN MULTICHANNEL THEORY OF ULTRACOLD COLLISIONS MODIFIED BYINTENSE LIGHT FIELDS TUNED TO THE RED OF THE TRAPPING TRANSITION

We develop a systematic scheme to treat binary collisions between ultr acold atoms in the presence of a strong laser field, tuned to the red of the trapping transition. We assume that the Rabi frequency is much less than the spacing between adjacent bound-state resonances, In this approach we neglect fine and hyperfine structures, but consider fully the three-dimensional aspects of the scattering process, up to the pa rtial d wave. We apply the scheme to calculate the S matrix elements u p to the second order in the ratio between the Rabi frequency and the laser detuning, We also obtain, fur this simplified multichannel model , the asymmetric line shapes of photoassociation spectroscopy, and the modification of the scattering length due to the light field at low, but finite, entrance kinetic energy. We emphasize that the present cal culations can be generalized to treat more realistic models, and sugge st how to carry out a thorough numerical comparison to this semianalyt ic theory. [S1050-2947(98)04902-6].