  We have measured the intensity dependent rate and frequency shift of a
photoassociation transition in a quantum degenerate gas of 7Li. The rate
increases linearly with photoassociation laser intensity for low intensities,
whereas saturation is observed at higher intensities. The measured rates and
shifts agree reasonably well with theory within the estimated systematic
uncertainties. Several theoretically predicted saturation mechanisms are
discussed, but a theory in which saturation arises because of quantum
mechanical unitarity agrees well with the data.
