High-resolution two-photon millimetre spectroscopy in sodium Rydberg states: possible applications to metrology

Abstract

The authors have observed very narrow two-photon millimetre resonances in sodium, corresponding to nS to (n+1)S transitions (principal quantum number n ranging from 32 to 40). The linewidth, of the order of 10 kHz for frequencies around 100 GHz, is transit-time limited. The variation with n of the quantum defects in the nS series is studied. The precision of the experiments can still be improved and applications to metrology and to a direct frequency determination of the Rydberg constant are possible.