Spectral line broadening due to the interaction between very excited atoms: 'the dense Rydberg gas'

Abstract

The authors report the first observation of spectral line perturbations, due to van der Waals coupling between very excited atoms, in a sample where the average interatomic distance is about 15 times the Rydberg atom radius. Broadenings of the order of intervals between adjacent lines reveal Rydberg-Rydberg couplings no longer negligible compared with the atomic binding energy. The authors analyse the excitation mechanism of this 'dense Rydberg gas' by laser light non-resonant for the unperturbed atoms.