Estimation of the end-to-end phase shift without beam reversal in Cs beam frequency standards

A new method is presented to directly determine the averaged phase difference φ between the fields interacting with the atoms in the two regions of a Ramsey cavity. This method is based upon the sensitivity of the phase shift to the frequency modulation depth and to the microwave power. We show too that it is possible to cancel the phase shift whatever the value of φ. Experimental results in our standard are given and are compared with those obtained by the beam reversal method. We show that the beam reversal method could lead to erroneous evaluation in our case. When combined with a beam reversal operation, the proposed method enables the distributed phase shift to be measured. This method could allow φ to be determined in commercial clocks, which had been believed not to be measurable until now