LASER PHASED-ARRAY GENERATED ULTRASOUND FOR NONDESTRUCTIVE EVALUATIONOF CERAMIC MATERIALS

This paper describes the experimental application of a phased optical fiber array to transmit pulsed laser light to the free surface of Carb orundum CS-3 ceramic samples for ultrasonic nondestructive evaluation (NDE). The pulsed laser beams heat the surface of the ceramic rapidly, and can thermoelastically generate longitudinal, shear, and surface ( Rayleigh) waves. Without the optical fiber array all three wave modes are generated simultaneously, and no control over directivity or beamw idth is possible. The experimental results presented here indicate tha t the wave modes, beamwidth, and directivity of the generated ultrasou nd can be controlled by using the phased optical fiber array. Experime ntal directivity patterns for the laser phased array are compared to a simple theoretical model based on Rose's point source theory. The mod el predicts shear wave directivities better than either longitudinal o r surface waves. This work demonstrates some of the capabilities and l imitations of using laser-phased arrays on ceramics.