Photoacoustic phase spectrum of a layered sample

Based on the Rosencwaig-Gersho theory (RG), we have studied the PhotoAcoustic Phase Spectrum (PAPS) of a two-layer sample. The theoretical results are mainly verified by an experiment, in which an intact plant leaf is used as the sample. The ratio of the optical absorption coefficient to the thermal diffusion coefficient for the subsurface layer can be obtained from the theoretical formula using measured phase values. The spectrum formed by the ratios at different wavelengths is in a good agreement with those experimentally obtained by phaseresolved photoacoustic spectroscopy.