Testing optical clock calibration procedures: Absolute frequency measurement of rubidium 5S-7S two-photon transitions

We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with an optical frequency comb. The digital lock to the transition, the procedures of evaluating the accuracy budget and measurements of the frequency with the optical frequency comb are tested with a simple setup for the sake of comparison of two optical lattice strontium clocks. The narrow, two-photon transition, 5S-7S (760 nm) is insensitive to a magnetic field and promising candidate for frequency standard. The preformed tests yield the transition frequency with accuracy better than reported previously.