Pulse train single-photon induced optical Ramsey fringes

The fluorescence signal from an atom or molecule following its single-photon near-resonant interaction with a train of N phase-coherent Gaussian pulses is calculated within the rotating-wave and first-order Magnus approximations. The Gaussian line shape will be flanked by Ramsey fringes whose widths are inversely proportional to N, provided the time delay of the train is an integral multiple of the carrier period. The signal intensity is proportional to $N^2$.