Metrological characterization of the pulsed Rb clock with optical detection

Abstract

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