[Optoacoustic spectroscopy and imaging]

Optoacoustic methods are based on the thermoelastic effect, according to which a short laser pulse is absorbed in a medium and generates an acoustic wave following rapid heating and thermal expansion. This study it sought to demonstrate how the optical properties and structure of the sample can be obtained from acoustic signals that are measured on the surface of the medium. This was pursued on the hand by using broadband piezo-electric and optical sensors, and on the other hand by means of theoretical simulations. For optically one-dimensional media, where the optical properties depend only on one direction in space, the measurement of a plane wave in the acoustical near field of the sample yielded directly the depth distribution of absorbed energy. In the far field, this simple relationship was not valid, due to acoustic diffraction. The distribution, however, could be reconstructed mathematically. Far field signals could also be used to image the contours of optical structures.