Determination of the absolute optical absorption coefficient for thermally thick samples by photoacoustic spectroscopy

A non-resonant photoacoustic cell, especially designed to optimize the signal-to-noise ratio, has been built. Following the Rosencwaig and Gersho theory, anew model has been developed for the quantitative determination of the optical absorption coefficient of thermally thick samples, by the simultaneous analysis of the amplitude and the phase of the photoacoustic signal. Tests have been performed on synthetic samples, in order to verify the applicability of the method in the cases of both single and double absorbing layers and a comparison has been carried out with the values of the optical absorption coefficient evaluated by transmission measurements, obtaining an agreement within 5%. The high quality of the response of the cell and the confidence of the method make it suitable for the determination of the optical absorption coefficient of biological samples, that can not be studied with traditional spectroscopic techniques because of their inhomogeneities and complexities. Preliminary results have been obtained on blood and on normal and pathological skin.