Thermal characterization of nonhomogeneous materials by photothermal radiometry

Although the mechanism of heat transport is a typical diffusion process, in cases in which the heat source is of a sinusoidal type, it may be found convenient to transform the Fourier diffusion equation in a formal Helmolz equation, speaking of thermal waves. In the present paper we will use this formalism for handling data from a photothermal measurement to retrieve the profile of thermal diffusivity under the surface of a solid material, showing that the surface temperature field obtained by the photothermal method can be connected to the thermal properties of the material in a simple and elegant way by using the concept of thermal waves scattering by the small thermal inhomogeneities of the material.