Pulsed optically pumped Rb clock: A high stability vapor cell frequency standard

In this paper we report the results we obtained with a prototype of pulsed optically pumped (POP) Rb clock. In terms of frequency stability, an Allan deviation σ_y(τ)=1.7 ×10^-13 τ^-1/2 has been measured, where τ is the integration time. In addition, the long term frequency drift results below 10^-14/day. In the paper we also describe a technique to stabilize the amplitude of the microwave signal using the atoms themselves as discriminator. Moreover, an anomalously large temperature sensitivity of the clock frequency and a technique to keep it under control are also reported. Finally, we describe some non linear effects that modify the shape of the clock signal represented by the Ramsey central fringe.