Phase and light shift determination in an optically pumped cesium beam frequency standard

The determination of the phase shift and the light shift in our optically p umped Cs beam is reported here. We show that an error on the phase differen ce value determined by our fit method, without beam reversal, can be induce d if the light shift is not taken into account. If the experimental data ar e corrected for the light shift, the results of the fit method are in very good agreement with the beam reversal results. This allows us to reduce the related uncertainty in the accuracy budget of our standard. The resulting overall accuracy of the standard is now estimated to be 6.3 x 10(-15).