Quantitative Photoacoustic Spectroscopy in the Frequency Domain

In this paper, the development of a new methodology for the quantitative determination of the optical absorption coefficient in simple systems in which the light absorption follows Beer's law is described. An approximation of the heat diffusion model of the photoacoustic effect for thermally thick samples is explored. It was found that we could combine the amplitude and the phase of the photoacoustic signal to obtain a new analytical expression for the optical absorption coefficient. This expression is directly proportional to the normalized photoacoustic signal amplitude, the sine of the phase difference, and the heat capacity per unit of volume of the sample. The theoretical results were experimentally verified in the visible range (300 nm to 700 nm). The optical absorption coefficient obtained with this methodology was comparable to that obtained by UV-Vis spectroscopy.