Simultaneous Measurements of Thermal Relaxation Times and Thermal Diffusivity at Low Temperature by Transient Laser-Heating Technique

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The transient temperature measurement gives approaches to not only high-speed measurement of thermophysical properties but also some new phenomena in heat conduction. In this work, the temperature dependency of optical reflectivity is determined by a laser ellipsometer at a wavelength of 632.8 nm in the range of low temperature. A transient reflectance measurement system is developed for measuring the transient temperature responses in range of 10 K to 300 K by using the continuous wave probing technique. The front surface of a foil specimen is heated by a laser-pulse irradiation. In situ measurement of the reflectivity of a continuous wave laser at the rear surface is conducted, the transient temperature response of film is then deduced using the temperature dependence of reflectivity. A general method for estimating the thermal diffusivity and relaxation parameters is given by the inverse analysis of generalized heat conduction problem. The method is employed to deduce thermophysical properties by fitting theoretical formulae to the experimental data of temperature rise. The stainless steel foils are chosen as samples and the accuracy is examined by comparing with the theoretical temperature responses and the thermal diffusivity data from the literatures. What done in this work gives the theoretical and experimental preparations to study the non-Fourier phenomena in the future.