Determination of the Rydberg constant by direct frequency measurement

We have built a frequency chain to connect the frequencies of the 2S-8S/D two-photon transitions in hydrogen to two optical standards, the methane-stabilized He-Ne laser and the iodine-stabilized He-Ne laser. In this way, an optical frequency of atomic hydrogen is directly linked for the first time to the cesium clock without any interferometry. We deduce a new value for the Rydberg constant with an uncertainty of 2.2 parts in 10/sup 11/. This value is in very good agreement with published values. The same frequency scheme has been used to measure the frequencies of the 5S-5D two-photon transition in rubidium and 2/sup 3/S/sub 1/-3/sup 3/P/sub 0/ in helium.<
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