A rigorous theoretical model has been developed that describes the effects of optical saturation on the deflection signals in cw photothermal experiments. In this model the spatial profile of the excitation beam has been taken into account. Numerical calculations have been performed to determine the saturation behavior of the cw photothermal deflection signals at both the fundamental and the second-harmonic frequencies for sine-wave modulation of the excitation beam. Saturation behavior for square-wave modulation has also been investigated.
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