Saturation of an atomic transition by a phase-diffusing laser field.

We have studied the effect of well-characterized laser frequency fluctuations on the saturation of an atomic resonance in a double optical resonance experiment. The peak-height asymmetry of the observed Autler-Townes signal was reversed at small detunings when the shape of the saturating laser power spectrum was changed from nearly Gaussian to nearly Lorentzian. This behavior agrees qualitatively with theoretical calculations and also with previous observations using lasers without such well-characterized fluctuations.