Cavity Phase Dependent Frequency Shifts in Cesium Beam Frequency Standards

The influence of the atomic velocity distribution in cesium beam atomic frequency standards on the frequency shift due to Ramsey cavity phase difference is discussed. The atomic resonance is shifted and its shape distorted to a degree dependent not only on the exciting power level and cavity phase difference, but also on the actual velocity distribution which exists in the standard. Calculations carried out for the NRC 2.1 metre primary standard show that, for the velocity distribution which probably exists in this standard, the resonance distortion gives rise to a power dependence of the frequency shift of about an order of magnitude less than that expected for a Maxwellian velocity distribution in the beam. Experimental measurements tend to support this result.