FREQUENCY-SHIFTS IN CESIUM BEAM CLOCKS INDUCED BY MICROWAVE LEAKAGES

The anomalous sensitivity of an optically pumped cesium beam clock to microwave power and the unexpected frequency shifts observed are demon strated to result from microwave leakages outside the arms of the Rams ey cavity. A new design of the cavity associated with a careful realis ation provides very weak microwave leakages and negligible related fre quency offsets. We have established a theoretical model that allows us to calculate the frequency shifts due to microwave field components p ropagating along the beam axis in regions which are free-field in an i deal Ramsey cavity. This results in first order Doppler effect shifts. The order of magnitude of the frequency shift can be predicted and ag rees with the measured one when the amplitude of the leakage magnetic field is about a 1000 times smaller than the amplitude of the microwav e interrogation field in the cavity.