Role of velocity induced coherent population oscillation in saturated fluorescence spectroscopy

In this paper we present a theoretical framework to identify the role of coherent population oscillation (CPO) in saturated fluorescence spectroscopy in a two-level system which is a very useful spectroscopic technique for weak transitions. The fluorescence dip in a fluorescence spectra is generally explained as a saturation effect. However in this work, we find that the Doppler-free dip in a fluorescence spectra is due to saturation effect and CPO effect. The fluorescence dip is further modified by Doppler averaging and its linewidth and dip height are dependent on the temperature of the atomic gas and the applied laser beam intensity. For an atomic beam, the shift of the fluorescence dip from the line center is dependent on the average velocity of the atomic beam and the misalignment of the laser beams with respect to the atomic beam.