RESONANT COLLISIONAL ENERGY-TRANSFER BETWEEN RYDBERG ATOMS

Resonant collisional energy transfer between atoms and molecules is of practical importance and is interesting in its own right as a long range collision process. Resonant dipole-dipole energy transfer collisions between Rydberg atoms provide an excellent system in which to explore these collisions in great detail. In particular, the large cross sections and long collision times make it possible to carry out otherwise impossible experiments. The theory of such collisions is presented from several points of view to describe the observed phenomena and to show the similarities to conventional resonance spectroscopy. The experimental dependence of the linewidths of the collisional resonances and the peak cross sections on principal quantum number, i.e the size of the dipole moments, and collision velocity is presented. Of particular interest, at very low collision velocities transform limited collisional resonances, in which the collision time is controlled externally, can be observed. Detailed investigations of the dependence of the lineshapes on the orientation of the collision velocity relative to a tuning electric field are also described. These measurements show a clear intracollisional interference analogous to the Ramsey interference pattern seen in radiofrequency spectroscopy. One of the more interesting applications of these collisions is to the study of radiatively assisted collisions, collisions involving the absorption or emission of photons. The theory of collisions between dressed molecular states is presented as well as experimental observations of high order multiphoton radiatively assisted collisions which substantiate the theory.