A radiometric method for measuring the thermal diffusivity of solids is presented. This method is based on the dynamic detection of an ac-temperature three-dimensional-distribution induced by the application of a localized and periodic optical excitation. Specifically the signal phase profile of the ac-temperature was detected along the sample surface. This procedure gives direct information on the material thermal diffusion length and, therefore, on its thermal diffusivity. Measurements on different bulk materials (i.e., Poco Graphite AXM-5Q, Armco Iron, Al2O3, and ZrO2) were performed and compared to the data obtained by the laser-flash method on the same set of samples. A further investigation on a very thin Si specimen (292 μm) showed the effect of thermal wave reflections at the sample backsurface on the measured thermal diffusivity. All the data obtained with this technique agreed to within 5% with those obtained using the laser-flash method and with the values taken from the literature for similar materials. Values in the range (8×10−7–0.9×10−4 m2/s) were obtained.

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