Lne-Syrte Clock Ensemble: New Rb-87 Hyperfine Frequency Measurement - Spectroscopy Of Hg-199 And Hg-201 Optical Clock Transition

This article describes recent frequency measurements performed with the LNE-SYRTE atomic clock ensemble. First, we report a new determination of the rubidium 87 hyperfine frequency, performed using Rb and Cs atomic fountains. The measurement has a statistical uncertainty below 10(-16) and an overall uncertainty of 1.1 parts in 10(15). Second, we report the first laser spectroscopy of the S-1(0)-P-3(0) optical clock transition at 265.6 nm in laser-cooled fermionic isotopes of neutral mercury. The absolute frequency is measured with a fractional uncertainty of similar to 5 parts in 10(12) which improves upon previous indirect determinations by more than 4 orders of magnitude, an important step toward the realization of an optical lattice clock.