Photoacoustics: a hundred years old technique revisited

A sample is heated when it absorbs light. The authors investigate the different ways of detecting the temperature increase produced by this heating in the case of solids. If the light is modulated, one can either detect mechanical vibrations induced in the fluid surrounding the solid (photoacoustic effect) or measure the deflection undergone by a laser beam probe whose axis is parallel to the solid surface (mirage effect). As an example of the use of these methods, the authors briefly review the study of optically imperfect or diffusing samples, and of highly absorbing or transparent media, determining their thermal properties.