title: High-precision optical measurement of the 2S hyperfine interval in atomic hydrogen.
abstract: We have applied an optical method to the measurement of the 2S hyperfine interval in atomic hydrogen. The interval has been measured by means of two-photon spectroscopy of the 1S-2S transition on a hydrogen atomic beam shielded from external magnetic fields. The measured value of the 2S hyperfine interval is equal to 177 556 860(16) Hz and represents the most precise measurement of this interval to date. The theoretical evaluation of the specific combination of 1S and 2S hyperfine intervals D21 is in fair agreement (within 1.4 sigma) with the value for D21 deduced from our measurement.
authors.affiliation: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Kolachevsky
authors.forename: M
authors.initials: M
authors.lastname: Fischer
authors.forename: S G
authors.initials: SG
authors.lastname: Karshenboim
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch