Metrological characterization of the pulsed Rb clock with optical detection

We report on the implementation and metrological characterization of a vapour-cell Rb frequency standard working in a pulsed regime. The three main parts of the clock, physics package, optics and electronics, are described in detail in this paper. The prototype is designed and optimized to detect the clock transition in the optical domain. Specifically, the reference atomic transition, excited with a Ramsey scheme, is detected by observing the interference pattern on a laser absorption signal. The metrological analysis includes the observation and characterization of the clock signal and the measurement of frequency stability and drift. In terms of Allan deviation, the measured frequency stability is as low as 1.7 × 10^−13 τ^−1/2 , τ being the averaging time, and reaches the value of a few units of 10^−15 for τ = 10^4 s, an unprecedented result for a vapour-cell clock. We discuss the physical effects leading to this result in this paper with particular care to laser and microwave noises transferred to the clock signal. The frequency drift, probably related to temperature, stays below 10−14 per day, and no evidence of flicker floor is observed. We also mention some possible improvements that in principle would lead to a clock stability below the 10−13 level at 1 s and to a drift of a few units of 10−15 per day