Radiative Rydberg-atom–Rydberg-atom collisions in the strong-field regime

We describe the experimental observation of the resonant collisional energy transfer Na(ns)+Na(ns)+qhν→Na(np)+Na[(n-1)p]+(q○)hν which occurs when the Na atoms in a strong microwave field are tuned in energy with a static field so that the energy resonance $E_{\mathrm{ns}}$+$E_{\mathrm{ns}}$=$E_{\mathrm{np}}$+$E_{n\mathrm{-}1}$,p±mhν occurs. We describe our experimental observations and provide a detailed description of a nonperturbative theory which we have developed to explain our observations. The theory is essentially developed in terms of the resonant dipole-dipole collisions between ‘‘microwave dressed’’ atoms. Using an extension of the approach we used previously to describe resonant dipole-dipole collisions in the absence of microwaves, we are able to take into account all the coherences in the problem in a completely straightforward way.