Photothermal investigations of thermal and optical properties of liquids by mirage effect

In this paper, the “mirage effect” detection technique was used in order to determine the thermal diffusivity and the absorption spectrum of liquids. Experiments were more particularly realized with paraffin oil.Generally, since the thermal diffusion length is relatively short in liquids, the different parts of the probe beam are differently deflected by the heat flow. So, a new mathematical expression of the deflection related to the probe beam dimensions was established to calculate the “effective” deflection in liquids. Such an expression was used to measure the thermal diffusivity of paraffin oil. Then, the “mirage effect” technique was also used to obtain indirectly the optical spectrum of paraffin oil through the measurement of the absorption of a carbon black layer immersed in this liquid.