Characterization of human skin through photoacoustic spectroscopy

The photoacoustic (PA) technique is based on the absorption of modulated or pulsed light by a sample with subsequent heat generation, generating thermal waves that propagate in the surrounding media. Such waves produce the pressure oscillation detected as the PA signal. In this work, PA spectroscopy was used to characterize different human skin samples with respect to their response to ultraviolet radiation (UVA and UVB, 240nm < $\lambda$ < 400nm). Measurements were performed at 70Hz and 17Hz, using a 1000W Xe arc lamp as the light source. Skin samples were about 0,5cm diameter. It was possible to obtain the absorption spectra of the stratum corneum and of a deeper layer of epidermis; when the lower modulation frequency is utilized, PA spectroscopy characterizes the absorption of the whole epidermis, because in this case the thermal diffusion length is thicker than that of the stratum corneum. PA spectroscopy was also employed to monitor the drying kinetics of the skin. Pre-treatment of the samples included different periods in a drying chamber. Measurements show that the PA spectra changes according to the humidity of the skin. Future work includes detailed monitoring of skin hydration