Development and absolute frequency measurement of a pair of 778 nm two-photon rubidium standards

A pair of diode laser frequency standards stabilized to 778 nm two-photon rubidium transitions have been developed and characterized. Their sensitivity to vapour pressure, modulation depth and optical power have been investigated, along with their relative stability and day-to-day reproducibility. The Allan deviation of the standards locked to the 5 2 S 1/2 ( F g = 3)–5 2 D 5/2 ( F e = 5) transition of 85 Rb is 9.3 × 10 −13 τ −1/2 for 1 s < τ < 100 s, reaching a floor of 1 × 10 −13 at 100 s. The long-term repeatability of an individual system locked to this line is 1.2 kHz, corresponding to 3.1 parts in 10 12 . The system-to-system reproducibility is limited by cell impurities to 4.9 kHz and 4.5 kHz, respectively, for this line and the 5 2 S 1/2 ( F g = 2)–5 2 D 5/2 ( F e = 4) transition in 87 Rb. The mean observed frequencies for these transitions, averaged for the two systems and corrected for light shift and second-order relativistic Doppler effect, are 385 285 142 375.1 (4.9) kHz and 385 284 566 374.2 (4.5) kHz, respectively.