Abstract
The conventional method of analysis used to investigate properties of molecules inside a medium consists of measuring the transmission and reflection coefficients of the material in order to determine the absorption of a given chromophore in the medium. However, this classical technique only gives access to an average value over the thickness of the material being investigated. It does not allow for the establishment of a depth profile of the density of chromophores in the material, i.e. their local concentration. In addition, this technique necessitates good optical quality of the medium in the range of the optical wavelengths used which makes it less suited to amorphous biological tissues because these are often subject to strong light diffusion, diffraction or a too high absorption. In contrast to this technique, photoacoustic spectroscopy (PAS) allows for the in-depth characterization of either homogenous or heterogenous non-transparent materials.1–4 This spectroscopy has already been applied to study complex biological media like leaves (photosynthesis)5–7, eye retina (vision)8–9 or human skin (membrane permeability).10–12