title: High-precision spectroscopy with counterpropagating femtosecond pulses.
abstract: An experimental realization of high-precision direct frequency comb spectroscopy using counterpropagating femtosecond pulses on two-photon atomic transitions is presented. The Doppler broadened background signal, hampering precision spectroscopy with ultrashort pulses, is effectively eliminated with a simple pulse shaping method. As a result, all four 5S-7S two-photon transitions in a rubidium vapor are determined with both statistical and systematic uncertainties below 10(-11), which is an order of magnitude better than previous experiments on these transitions.
authors.affiliation: Department of Physics and Astronomy, LaserLaB, VU University, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: Itan
authors.initials: I
authors.lastname: Barmes
authors.forename: Stefan
authors.initials: S
authors.lastname: Witte
authors.forename: Kjeld S E
authors.initials: KS
authors.lastname: Eikema