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Improving short and long term stability of pulsed optically pumped vapor cell frequency standards

In this paper we discuss how to improve both short and medium-long term frequency stability of a vapor cell frequency standard working in pulsed regime. We propose in particular a multi-step pumping technique that is able to put almost all the atoms in one of the two clock levels, increasing in this way the signal-to-noise ratio with respect to the usual optical pumping made with a single laser pulse. Moreover, we discuss the phenomena affecting the medium-long term frequency stability and how it is possible to control them, making the overall clock stability compatible with σ<inf>y</inf>(τ) =3×10<sup>−13</sup> τ <sup>−½</sup> for integration times up to τ = 10<sup>5</sup> s.