We propose a scheme of obtaining Ramsey fringes based on pulsed coherent optical information storage. Unlike the usual frequency references where the Ramsey fringes are obtained by detecting the population of a certain state, we get the Ramsey fringes by detecting the atomic coherence. The central line of the Ramsey fringes can be used as a frequency reference in an absorption-cell-based atomic frequency standard. This scheme is free of light shifts as the interrogating process is separated from the optical pumping process, and the cavity pulling effect is negligible due to the low $Q$ requirement. Encoding the Ramsey interference into the retrieval light pulse has the merit of high signal-to-noise ratio. This scheme is promising for building small, compact, and stable atomic clocks.

• Received 7 August 2008

DOI:https://doi.org/10.1103/PhysRevA.79.063820