Simple parameterization of dark-resonance line shapes

We have studied the dispersion and absorption line shapes of coherent population trapping resonances (dark resonances) in thermal cesium vapor. Outside the time-of-flight regime the line shapes can be described by a simple phenomenological model: a sum of a dispersive and an absorptive Lorentzian of identical width and position, whose relative weights depend on the detuning of the laser frequencies from the optical resonance. This functional form can be derived from a theoretical model for the full multilevel structure of an alkali atom. The analytical expressions for the parameters of the line shape model show the same behavior as the experimental data.