Analysis of Modulation Method for Measuring Atomic Resonant Frequency

In microwave spectroscopy and in atomic frequency standards, the atomic resonant frequency is often determied by the use of harmonic frequency modulation of a microwave signal. The effects of line asymmetry and modulating-signal nonlinear distortions are investigated by the use of an analytic approximation of the resonance line by means of an algebraic polynomial. The coefficients of the polynomial are determined experimentally and also derived theoretically. Detailed numerical results for a Ramsey resonance line in a cesium clock are given.