Visualization of Elastic Waves by Digital Laser Ultrasonics.

We have developed a laser ultrasonic system for a visualization of elastic waves propagating on a solid surface. Scanning an optical heterodyne probe to measure surface transient displacements, ultrasonic waves in the frequency range up to 50 MHz are detected and passed to a personal computer through a digital oscilloscope. The recorded signals are reconstructed to make 3-D displacement images at any propagation time. This system can produce a series of successive images as an animation of wave propagation. Using this visualization technique, we observed the scattering and diffraction of ultrasonic waves around various shapes of penetrations on aluminum plate, and examined its application to nondestructive inspection.