Suppression of Microwave Leakage Shifts in Fountain Clocks by Frequency Detuning

We present a method for the suppression of frequency shifts in pulsed atomic clocks based on the Ramsey scheme, caused by unwanted interaction of the atoms with the resonant interrogation field during the free atomic evolution time (Ramsey time). The method relies upon a precise control of the field's frequency detuning during the period of free evolution. The frequency detuning reduces the frequency shift caused by the interaction between the free precessing atoms and the interrogation field. We present measurements that allow us to limit the uncertainty contributions due to such an interaction at the atomic fountain clock PTB-CSF2 to 3.8 × 10
^-17
.