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 volumeabsorbing samples (colored optical glasses) and used successfully to calculate absorbances and concentrations for various surface-absorbing samples.