Abstract
This paper describes a method for measuring the thickness of a metal plate by making use of thermal elastic waves induced by intermittent irradiation of a CO2, laser beam with power density of 5×109 W/m2. Experiments are carried out for five kinds of metal samples including aluminum and copper with a thickness range between 0.1×10-3 and 2×10-3 m. The following results are obtained: (1) The modulation frequency which makes phase angle of the thermal elastic wave zero degree is reciprocally proportional to square of the thickness. (2) The modulation frequency is determined by thermal diffusibility of each metal. (3) The product of optical absorption coefficient multiplied by sample of thickness is 1.57. On the basis of these results, a method for obtaining optical absorption coefficient is also discussed.
