First-order sideband pulling in atomic frequency standards

High performance frequency standards, including cesium fountains and most optical standards, operate with pulsed measurements repeated at a fixed frequency. By introducing frequency modulation of the excitation coherent with the measurement cycle time, we have observed biases in the primary frequency standard NIST-F1 much larger than biases predicted by previous theories. We derive a theory of such biases for both Rabi and Ramsey excitation. We find agreement with the experimental measurements.