Laser-ultrasonic sensing of surface temperature distribution of a material being heated

A new non-contact method with a laser ultrasonic technique for measuring surface temperature distribution of a material being heated is presented. The principle of the surface temperature measurement is based on temperature dependence of the velocity of the surface acoustic wave (SAW) propagating on a material surface. An effective method consisting of a SAW velocity measurement and an inverse analysis coupled with a one-dimensional finite difference calculation has been developed to determine surface temperature distributions quantitatively. In order to demonstrate the practical feasibility of the method, surface temperature distributions of a steel and aluminium plates are examined. The SAW of each plate is measured during heating using a laser ultrasound interferometer based on photorefractive two-wave mixing. The surface temperature distributions determined by the ultrasonic method almost agree with those measured using an infrared camera.