Optical saturation effects in intracavity Faraday modulation spectroscopy (INFAMOS).

We report on the observation of saturation effects in Intracavity Faraday Modulation Spectroscopy (INFAMOS). A quantum cascade laser operating at 5.3 m is used to probe the Π and Π R(3.5) transitions in the fundamental band of nitric oxide. With average intracavity intensities up to 450 W cm, the saturation of these molecular transitions is observed up to a total pressure of 240 Torr. The experimental data are interpreted by incorporating saturation into a model for the INFAMOS line shape in the homogeneously broadened limit.