Experiments in Cold and Ultracold Collisions

Abstract

This chapter discusses results from collisions within optical traps and atomic beams. Two-particle and light-field interactions characterize collision physics in the cold and ultracold kinetic energy regimes. Cross sections increasing by orders of magnitude and acute sensitivity to light-field intensity and polarization distinguish the new domain from conventional thermal environments. In the cold regime, alignment and orientation of the weakly interacting atomic populations control the collision probability, while in the ultracold regime, optical-field state dressing plays an indispensable role. Optical traps achieve temperatures at which kT approaches the natural width of an atomic line; however, as containers for collision experiments, they are essentially cells of very cold gas in which the distribution of collision directions is isotropic. Atomic beams, however, provide a principal laboratory axis and are therefore useful for studying the effects of orientation and alignment in collision problems. The single-beam technique can also be used to study the effects of optical-field state dressing, but a narrow velocity class must be isolated in one of the Na ground-state hyperfine levels so as to avoid an increased velocity dispersion by power broadening.