Model for continuous-wave laser-induced thermal lens spectrometry of optically transparent surface-absorbing solids.

A theoretical model for cw laser-induced thermal lens spectrometry of optically transparent surface-absorbing solids is developed. In the model, the sample is represented as a set of discrete layers with certain thicknesses and light absorptivities. The bloomed thermo-optical element in the sample is described with a summation of heat-flux functions for all the layers. The model employs simple mathematical expressions and can be used for both steady-state and time-resolved thermal lens experiments. Good coincidence of the experimental and theoretically predicted signal dependences is achieved. This model is verified for volume-absorbing samples (colored optical glasses) and used successfully to calculate absorbances and concentrations for various surface-absorbing samples.