title: Ultraprecise measurement of optical frequency ratios.
abstract: We developed a novel technique for frequency measurement and synthesis, based on the operation of a femtosecond comb generator as transfer oscillator. The technique can be used to measure frequency ratios of any optical signals throughout the visible and near-infrared part of the spectrum. Relative uncertainties of 10(-18) for averaging times of 100 s are possible. Using a Nd:YAG laser in combination with a nonlinear crystal we measured the frequency ratio of the second harmonic nu(SH) at 532 nm to the fundamental nu(0) at 1064 nm, nu(SH)/nu(0) = 2.000 000 000 000 000 001x (1 +/- 7x10(-19)).
authors.affiliation: Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Stenger
authors.forename: Harald
authors.initials: H
authors.lastname: Schnatz
authors.forename: Christian
authors.initials: C
authors.lastname: Tamm
authors.forename: Harald R
authors.initials: HR
authors.lastname: Telle