QUANTUM AND SEMICLASSICAL CALCULATIONS OF COLD-ATOM COLLISIONS IN LIGHT FIELDS

We derive and apply an optical Bloch equation (OBE) model for describi ng collisions of ground and excited laser cooled alkali atoms in the p resence of near-resonant light. Typically these collisions lead to los s of atoms from traps. We compare the results obtained with a quantum mechanical complex potential treatment, semiclassical Landau-Zener mod els with decay, and a quantum time-dependent Monte Carlo wave packet ( MCWP) calculation. We formulate the OBE method in both adiabatic and d iabatic representations. We calculate the laser intensity dependence o f collision probabilities and find that the adiabatic OBE results agre e quantitatively with those of the MCWP calculation, and qualitatively with the semiclassical Landau-Zener model with delayed decay, but tha t the complex potential method or the traditional Landau-Zener model f ail in the saturation limit.