First-Order Sideband Pulling in Atomic Frequency Standards

Many high-performance atomic frequency standards, including cesium fountains and most optical standards, operate with pulsed measurements, that is, an atomic sample is prepared for measurement, the measurement is made, and the process is repeated at fixed intervals. By introducing frequency modulation of the excitation coherent with the measurement cycle time, we have observed biases in our primary frequency standard NIST-F1 that are much larger than the biases predicted by previous theories. We derive a theory of such biases for both Rabi and Ramsey excitations. We find agreement with the experimental measurements.