Measurement of the 1S-2S frequency in atomic hydrogen.

Abstract

We report on a first precise measurement of the 1S-2S energy interval in atomic hydrogen. Observing the 1S-2S transition in an atomic beam by pulsed Doppler-free two-photon spectroscopy and using an interferometrically calibrated absorption line of $^{130}\mathrm{Te}_{2}$ at 486 nm as the reference, we measure the frequency f(1S-2S)=2 466 061 395.6(4.8) MHz. Using the calculated 1S Lamb shift, we obtain a value for the Rydberg constant, ${\mathrm{R}}_{\mathrm{\ensuremath{\infty}}}$=109 737.314 92(22) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, which is not in good agreement with the most recent previous measurement.