Confocal micro-Raman spectroscopy: Theory and application to a hybrid polymer coating

Confocal micro-Raman spectroscope has been applied for vibrational investigations on a sol-gel derived hybrid poly mer coating. In order to characterize the dimensions of the focus inside the coating, the substrate. and the coating/substrate, a model that considers both the refraction and diffraction effects has been developed. A coating of similar to20.2 mum thickness applied to polycarbonate substrate has been investigated. The spatial distribution of the Raman intensity in the focal volume was studied at different depths within the sample and the Raman response at the corresponding levels has been calculated. The selection in depth of the Raman response, given by the confocal pinhole, was also taken into account. In comparing the prediction of this theoretical model to the empirical results, a good agreement has been observed.