Anisotropic fluorescence signals retarded dipole-dipole interactions in a thermal atomic cloud

Abstract

We experimentally observe and theoretically explain anisotropic multiple quantum coherence signals in the fluorescence from dilute thermal potassium vapors, at room temperature and particle densities $\sim 10^8{\mathrm{cm}}^{-3}$. We identify the retarded part of the geometrically fully resolved inter-atomic, resonant dipole-dipole interaction as the crucial ingredient to theoretically reproduce all qualitative features of the experimental spectra.

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