Ultrasonics With Laser In-Coupling and Air Out-Coupling

Efforts are under way to develop a technique of noncontact acousto-ultrasonic testing in which (1) a pulsed laser beam excites ultrasonic waves in a plate specimen and (2) the ultrasonic waves are detected by use of one or more focusing air-coupled ultrasonic transducer(s) placed at a short distance away from the specimen and aimed at the spot(s) of interest on the specimen. This technique is intended to be an alternative to an older technique of contact acousto-ultrasonic testing; when fully developed, this noncontact technique could be used to characterize materials and monitor integrity of structures in locations that are inaccessible to contact ultrasonic probes or in situations in which contact ultrasonic probes cannot or should not be used.