Low-Temperature Thermal Diffusivity Measurement by Laser-Flash Method

抄録

The pulse heating method has been developed for measuring the thermal diffusivity of solids at low temperatures. The experimental procedures were such that the front surface of a disk-shaped specimen was irradiated by a ruby-laser pulse (pulse width<1 msec), and the time variation of the temperature at the rear surface was detected by thin-film bolometers (sputtered gold film at higher temperatures and painted carbon film at lower temperatures) and was recorded by a sensitive high-speed electronic apparatus. The measurements were made at temperatures between 300 and 4.2 K, and the specimen used were polyethylene (60% crystallinity). The method to analyze the experimental data was precisely described. It was shown that the finite pulse-time effect could be ignored due to the short duration of the laser pulse, and that the consideration should be made on the heat loss from the specimen to its surroundings through the heat conduction, and also that an adequate choice of the bolometers was important especially at lower temperatures.