Studies on the accurate evaluation of the RRL primary cesium beam frequency standard

In order to set the C field, we use both field-dependent transitions, (F = 4, mF = + 1) → (F = 3, mF = ±1), to control the fluctuation and to compensate the effect of C field uniformity. The side-lobes of these transitions pull the center frequency of clock transition. Their effect can be estimated by assuming that holes for the beams and the cutoff waveguide disturb the microwave along the beam path and distort the microwave field. This disturbance may cause the first-order Doppler shift. On this supposition, we checked the microwave power-dependent frequency shift by changing the beam velocity. Recently, this power-dependent shift has been decreased to our satisfaction. This improvement has probably resulted from the recent optimization of the beam optics.