Simulation of photoacoustic IR spectra of multilayer structures

In photoacoustic spectroscopy a sample in a closed gas cell is heated by periodically modulated light. When thermal waves generated by the warm spots inside the sample reach the surface they heat up the adjacent gas. This causes periodic pressure variations which are detected by a microphone. We present a matrix method which enables us to calculate the surface temperature of a multilayer structure with any number of homogeneous lamellae of any optical and thermal properties. This method is based on the multiple reflections and interferences of thermal waves inside the system of lamellae. Photoacoustic spectra simulated by this method reproduce the measured spectra. This is demonstrated for a mylar (polyethyleneterephthalate, PETP) foil coated with a thin antimony layer.