Inspection of Components Having Complex Geometries Using Laser-Based Ultrasound

Abstract

Laser-based ultrasound (LBU) has a number of distinct advantages compared with conventional contact piezoelectric transducer systems. The LBU technique is noncontacting and the laser beams conform to the part surface so that couplant nonuniformities and the need for maintaining normality to, and fixed distance from, the part are eliminated. The LBU technique thus potentially allows rapid, and close to 100%, inspections of complexly contoured surfaces. Various laser techniques used to generate and receive ultrasonic waves have been reviewed by several authors [1–2]. While the generation and detection procedures employed by LBU are distinctly different from systems employing piezoelectric transducers, once ultrasound is generated by a laser, it propagates into a material and interacts with defects in precisely the same way. Thus, laser-based ultrasound can provide inspection resolution comparable to that which can be obtained using commercially available ultrasonic squirter systems, which require water coupling to the part.