Effective thermal conductivity: Application to photothermal experiments for the case of bulk light absorption

We suggest a new theoretical approach to obtain effective thermal parameters of two-layer structures in photothermal experiments, and calculate the effective thermal conductivity in the quasistatic approximation. Unlike previous works devoted to this problem, it is supposed that a non-equilibrium temperature originates due to the bulk modulated light absorption. It is shown that in this case the effective thermal parameters have to be obtained together with the effective optical parameters. As a result, the effective thermal parameters in the general case are dependent on the optical parameters of the layers. The role of the thermal properties of the interface between the layers is discussed. It is concluded that the effective parameters are not single-valued. They depend on the manner of measurements and the point of these measurements.