New attempt for measuring thermal diffusivity of thin films by means of a laser flash method

Abstract

A new facility and its requirements have been developed for the measurement of the thermal diffusivity of thin films or ribbons which are less than about 100 μm in thickness, using a laser flash method. In this method, a pulsed laser beam which has a narrow line-shaped cross section compared with the length of the sample is flashed onto the front surface of the sample. The temperature response at the back surface at a certain distance away from the line-shaped illuminated area of the laser beam is measured by an infrared detector. The thermal diffusivity value can be estimated from the time required for the temperature to reach the half of the maximum temperature rise finally acquired. The usefulness of the present facility has been demonstrated by measuring successfully thermal diffusivities of thin foils of platinum (25 μm) and of copper (18 μm). This method can be applied to the samples having various thermal diffusivities, particularly in cases where the conventional method using a thermocouple is found to be technically difficult. For example, a thin fragile sample for which it is almost impossible to weld the temperature detecting device onto it.