Simultaneous measurement of the in-plane and in-depth thermal diffusivity of solids using pulsed infrared thermography with focused illumination

We extend the flash method to retrieve simultaneously the principal in-plane and the in-depth thermal diffusivities of anisotropic solids using focused Gaussian illumination. A complete theoretical model allows calculating the temperature rise of an anisotropic and semitransparent sample. The surface temperature distribution has a Gaussian shape along the principal axes, whose radii give the principal inplane thermal diffusivities. On the other hand, the time evolution of the spatially averaged surface temperature gives the principal in-depth thermal diffusivity. Measurements performed on opaque and semitransparent samples, covering a wide range of thermal diffusivities, validate the method. It is especially suited to characterize the principal components of the thermal diffusivity tensor of anisotropic plates from a single and fast measurement. (C) 2015 Elsevier Ltd. All rights reserved.