Development of AC Calorimetric Method for Thermal Diffusivity Measurement V. Modulated Laser Beam Irradiation

In an ac light-irradiation method for measuring thermal diffusivity along the length of the rectangular thin film sample, we developed a method which uses a modulated laser beam. The laser beam was swept with a high frequency so as to cover the width of the sample. Such a procedure makes possible to obtain uniform ac thermal energy distribution in the direction perpendicular to the direction of ac temperature-wave propagation. Furthermore, it gives rise to a nonuniform ac thermal energy distribution in the direction along the direction of ac temperature-wave propagation. It is theoretically proven that the latter inhomogeneity does not affect the determination of thermal diffusivity. This fact is verified by experiment.