Dipole-dipole collision-induced transport of resonance excitation in a high-density atomic vapor

Abstract

We have experimentally studied the nonradiative transport of excitation in a dense $[N$=(0.3-2.5)\ifmmode\times\else\texttimes\fi{}${10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}]$ potassium vapor. We show that in such a high-density vapor the diffusive nonradiative transport of excitation via ``hopping'' of excitation in dipole-dipole collisions between excited- and ground-state atoms is dominant over the radiative transport through photons. The nonradiative transport mechanism becomes visible in the fluorescence-excitation spectrum signal as a sharp dip close to the resonance frequency. The appearance of the dip, its shape, width, and density dependence can all be explained in terms of a simple diffusion model for the nonradiative transport. This yields values for the diffusion coefficient and the resonance-exchange rate coefficient.