Laser Spot Periodic Heating Radiation Thermometry for Measuring Thermal Diffusivity of Anisotropic Materials

The accurate evaluation of in-plane and out-of-plane thermal diffusivities is crucial for thermally anisotropic materials.In this study, we propose a measurement and analysis framework based on laser spot periodic heating radiation thermometry for such materials.For in-plane thermal diffusivity, the conventional method based on the distance dependence of the phase lag was applied, while ensuring that the combined choice of modulation frequency and measurement distance range satisfied both the required number of thermal waves and the validity of the 1D heat-diffusion approximation.For out-of-plane thermal diffusivity, a finite element method was employed to reproduce effects that cannot be neglected under out-of-plane measurement conditions, including the finite spatial distributions of laser heating and thermal detection, as well as thermal-wave reflection at material surfaces.The validity of the proposed approach was first confirmed using a pure copper sample and well-established literature values, demonstrating that the appropriate wave-number selection and accurate reproduction of the measurement configuration lead to reliable thermal diffusivity evaluation.The methodology was then applied to graphite sheets as a demonstration case, and physically reasonable consistency with existing data was obtained.These results indicate that the proposed framework provides a practical and reliable method for evaluating anisotropic thermal diffusivity.