Direct Observation and Mechanism Study of the Dynamic Process of Thermal Expansion

In this work, CO2 laser pulse of 0.1 s was used to heat instantly the thin specimens of Al, constantan, BN with the thickness of 20~100 m, and a system of the slit diffraction using He-Ne laser was also adopted. By a photoelectric converting device, the change of the specimen length was transferred to the change of light strength, then to that of voltage. Using above method, we have observed and measured the changing process of the thermal expansion amount of the specimen with time during the specimen was heated instantly. For the first time, the dynamic-process of thermal expansion was observed directly and the oscillograms of the relaxation curves of thermal expansion were obtained. On the basis of above experiment, we have examed the relation between the relaxation time and the specimen length for Al. The mechanism of the dynamic-process of thermal expansion has also been discussed.