Niering M, Holzwarth R, Reichert J, Pokasov P, Udem T, Weitz M, Hansch TW, Lemonde P, Santarelli G, Abgrall M, Laurent P, Salomon C, Clairon A
Max-Planck-Institut fur Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany.
Phys Rev Lett. 2000 Jun 12;84(24):5496-9. doi: 10.1103/PhysRevLett.84.5496.
We report on an absolute frequency measurement of the hydrogen 1S-2S two-photon transition in a cold atomic beam with an accuracy of 1.8 parts in 10(14). Our experimental result of 2 466 061 413 187 103(46) Hz has been obtained by phase coherent comparison of the hydrogen transition frequency with an atomic cesium fountain clock. Both frequencies are linked with a comb of laser frequencies emitted by a mode locked laser.
