Laser ultrasonic studies of solid–liquid interfaces

A laser ultrasonic approach has been developed and used to measure the time-of-flight (TOF) for rays penetrating model cylindrical solid–liquid interfaces. Since the longitudinal acoustic wave speed in the solid is 45% higher than the liquid, TOF measurements for ultrasonic rays that propagate through the interface are found to be sensitive to the instantaneous position and shape of the interface. A ray tracing code (incorporating both interface refracted and creeping rays) has predicted the ray paths and their time-of-flights as a function of axial position for opposingly aligned source/receiver points on the diametral plane. When used in conjunction with a nonlinear least-squares method, the ray propagation model enabled reconstruction of the interface position, its convexity, and the velocities of both the liquid and solid phases from a few parallel beam TOF measurements collected on the diametral plane.