A new and simple approximation method for quantitative depth profiling using photoacoustic spectroscopy (PAS) is described. In the method, an approximate calculation of the inversion of the Laplace transform is adopted in order to simplify the calculation of the depth-dependent optical-absorption coefficient from photoacoustic frequency responses. Some results of simulations shown demonstrate the effectiveness of this method. The method has been applied to the depth profiling of the practical sample in which the optical-absorption coefficient varies continuously with the depth from the surface. The result is qualitatively consistent with microscopic observations of the cross section of the specimen. This approximation could be useful not only for the depth profile with PAS but also for the general depth profile calculations based on the Laplace transformation.
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