In-depth analysis of the frequency stability of optically pumped cesium beam frequency standards

In the frame of an ESA contract aiming at the feasibility study of a compact, very stable, optically pumped cesium beam clock for Galileo, we have completed our previous analysis of the frequency stability of such a frequency reference. This analysis concerns the single optical frequency configuration. All possible noise sources are considered. Optimum operating conditions providing the best frequency stability are defined and presented It is shown, and justified by simple arguments, that a resonator using a microwave cavity with a phase difference phi = pi between the two oscillatory fields may either provide a better frequency stability than a cavity of the same length but with phi= 0, or provide a given frequency stability with a cesium consumption significantly lower than in the phi=0 configuration. The analysis is applied to the OSCAR resonator conceived and operated at Observatoire de Neuchatel, with two different operating conditions that provide very high performances: the theoretical and experimental results are in excellent agreement. It is concluded that the presented analysis can be safely used to design very high performance, compact, optically pumped cesium beam clocks.