title: Precision spectroscopy of hydrogen and femtosecond laser frequency combs.
abstract: Precision spectroscopy of the simple hydrogen atom has inspired dramatic advances in optical frequency metrology: femtosecond laser optical frequency comb synthesizers have revolutionized the precise measurement of optical frequencies, and they provide a reliable clock mechanism for optical atomic clocks. Precision spectroscopy of the hydrogen 1S-2S two-photon resonance has reached an accuracy of 1.4 parts in 10(14), and considerable future improvements are envisioned. Such laboratory experiments are setting new limits for possible slow variations of the fine structure constant alpha and the magnetic moment of the caesium nucleus mu(Cs) in units of the Bohr magneton mu(B).
authors.affiliation: Department of Physics, Ludwig-Maximilians-Universität, München, Germany. t.w.haensch@physik.uni-munchen.de
authors.forename: T W
authors.initials: TW
authors.lastname: Hänsch
authors.forename: J
authors.initials: J
authors.lastname: Alnis
authors.forename: P
authors.initials: P
authors.lastname: Fendel
authors.forename: M
authors.initials: M
authors.lastname: Fischer
authors.forename: C
authors.initials: C
authors.lastname: Gohle
authors.forename: M
authors.initials: M
authors.lastname: Herrmann
authors.forename: R
authors.initials: R
authors.lastname: Holzwarth
authors.forename: N
authors.initials: N
authors.lastname: Kolachevsky
authors.forename: Th
authors.initials: T
authors.lastname: Udem
authors.forename: M
authors.initials: M
authors.lastname: Zimmermann
mesh_terms: D006859:Hydrogen / Q000032:analysis* / Q000592:standards*; D007394:International System of Units / Q000592:standards*; D038622:Internationality; D007834:Lasers; D010825:Physics / Q000592:standards; D011789:Quantum Theory; D012015:Reference Standards; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods* / Q000592:standards*
chemical_list: D006859:Hydrogen