Modelling and analysis of laser flash experiments using the Cattaneo heat equation

Thermal diffusivity of solid materials is commonly measured using laser flash analysis. This technique involves applying a heat pulse to the front surface of a small sample of the material and calculating the thermal diffusivity from the resulting increase in temperature on the back surface. Current formulas for the thermal diffusivity are based on the assumption that heat is transported within the sample according to the standard heat equation. While this assumption is valid in most practical cases, it admits the non-physical property of infinite propagation speed, that is, the heat pulse applied at the front surface is instantaneously perceived at the back surface. This paper carries out a mathematical analysis to determine the effect of replacing the standard heat equation in laser flash analysis by the Cattaneo heat equation, which exhibits finite propagation speed through the inclusion of a relaxation time in the Fourier law. The main results of the paper include (i) analytical insights into the spatiotemporal behaviour of temperature within the sample and (ii) analytical formulas for determining the thermal diffusivity and relaxation time of the sample. Numerical experiments exploring and verifying the analytical results are presented with supporting MATLAB code made publicly available.