High-order effects in Rayleigh-type optical mixing

A nonperturbative analysis (in one of the fields) of the Rayleigh-type optical-mixing signal in an absorbing medium shows that it is more sensible to saturation than the effect that could be expected from ``absorption saturation arguments.'' We also report the observation of such high-order effects in the organic dye malachite green. We have found that an effective two-level system model with a longitudinal relaxation time of 1.1±{}0.2 ps, a transverse relaxation time of 0.13±{}0.05 ps, and a transition moment of 1.2 D account for the deviation from the third-order regime. However, the frequency region of the data that follows the predicted spectral deformation is power dependent and it shrinks as power increases.