High Resolution Spectroscopy of the Hydrogen Atom. I. Method and Experiment

In order to determine the Rydberg constant R∞ to a very high accuracy, we have performed a Doppler-free two-photon absorption experiment on atomic hydrogen and deuterium. We have obtained a new value of R∞ which is in excellent agreement with other recent measurements and the most precise one at the present time. Here we give a detailed report on the method and apparatus we have used. A metastable beam of 2S H and D atoms has been prepared and laser excited to Rydberg nS and nD levels (n≽8) in a two-photon transition. The experimental geometry has been carefully designed to make the atomic beam collinear with the two counterpropagating laser beams. With this set-up we have observed very narrow resonances, with relative linewidths smaller than 10-9. Among all the transitions investigated we have selected three transitions (2S-8D, 2S-10D and 2S-12D) in hydrogen and deuterium to determine R ∞.