Coherent population trapping and Fano profiles

This paper presents a new approach to coherent population trapping in a A-type three level atomic configuration. This approach, which is based on scattering theory, applies when one of the two driving laser fields is much weaker than the other one. We show that the scattering amplitude of the weak field is the sum of 2 resonant amplitudes. The positions and the widths of these resonances are identified and physically interpreted in the low saturation limit, in terms of Rayleigh scattering, stimulated and spontaneous Raman scattering. Finally, we show that the interference between the two scattering amplitudes gives rise to Fano profiles in the curves giving the frequency dependence of the total scattering cross-section.