Mode conversion detection in an elastic plate based on Fizeau fiber interferometer

Based on laser ultrasonic techniques, the mode-converted waves in an aluminum plate with a rectangular groove have been investigated by a Fizeau fiber interferometer. A Q-switched Nd:YAG laser was used for ultrasonic generation, and mode conversions occurred when ultrasonic waves interacted with the groove. Increasing the distance between the detection point and the groove could lead to the obvious changes in time domain signals. Experimental results showed that the ultrasonic waves induced by the pulsed laser were extremely sensitive to the surface-breaking cracks due to elastic wave mode conversions, and as the distance increased, the discrimination between different mode-converted waves was gradually enhanced. Furthermore, the depth of the groove was quantitatively measured through the analysis of the mode-converted Rayleigh waves. Our interferometer exhibited an outstanding performance in detecting elastic waves, which could be used not only in exploring the mechanism of mode conversions but also in evaluating structure cracks.