IMPROVED PERFORMANCES IN Cs STANDARDS WITH NEW-DESIGN RESONATORS

Abstract
The problems that limit the accuracy of present state-of-the-art Cs beam primary frequency standards are related to atoms' velocity distribution, cavity-phase-difference and magnetic field inhomogeneity. Improvements of this situation may be introduced by optical state selection and detection, but only a redesigned microwave structure using open Fabry-Perot resonators allows thorough exploitation of this technique by permitting the use of very wide beams. The high signal-to-noise ratio obtained in this way can be spent in different ways for frequency accuracy enhancement. Two configurations are proposed : a two-cavities horizontal wide beam and a single cavity fountain beam. Projected stability and accuracy performances are reported for the two schemes ; improvements of stability down to the 10^-13 level and accuracies from few parts in 10^-14 to better than 10^-15 are expected.