The PTB's Atomic Frequency Standards CS2 and CSX: Frequency Shifts by Pulling due to Neighbouring Transitions

The frequency-shifting effect that neighbouring lines have on the clock transition of the PTB's frequency standards CS 2 and CSX is experimentally and theoretically investigated. The measurements confirm the model underlying the calculations, which allows for the consinusoidal field distribution in the end parts of the Ramsey cavity, the velocity distribution of the Cs atoms and the population of the hyperfine sublevels. At the normal value of the static magnetic field usually called the C-field of CS 2, a reliable estimate of the frequency uncertainty contribution due to Rabi pulling is below 1 × 10-16.