Frequency stability of a pulsed optically pumped atomic clock with narrow Ramsey linewidth.

In general, the linewidth of the Ramsey central fringe (RCF) is equal to 1/(2T), where T is the Ramsey free-evolution time. We demonstrate that the RCF linewidth of a pulsed optically pumped (POP) atomic clock with orthogonal polarization detection based on the magneto-optical rotation effect can be narrowed down to 1/(4T). The Allan deviation of the POP atomic clock decreases from 2.4×10-13 τ-1/2 to 1.4×10-13 τ-1/2 . This corresponds to an improvement in the frequency stability by about 60%. We also estimate the main noise sources that limit the short-term frequency stability of the POP atomic clock.