Ultracold collisions in saturating optical fields: Universal behavior in the entrance channel - art. no. 011404

We present precise near-dissociation limit measurements of ultracold collis ion rate constants (trap loss, fine-structure changing, and photoassociativ e ionization) as a function of trap intensity from I-sat to I approximate t o 40I(sat) for Cs and Na atoms cooled and confined in a magneto-optical tra p. We find strong saturation fur all processes at intensities approximately 10 times the free atom saturation level I-sat. Our results provide a preci se reference point for testing and comparing different theoretical models u sed to analyze ultracold collisions.