NONCONTACT ULTRASONIC-IMAGING OF SUBSURFACE DEFECTS USING A LASER-ULTRASONIC TECHNIQUE

Noncontact ultrasonic imaging of subsurface defects using a laser-ultr asonic technique was demonstrated. Pulsed laser irradiation was used f or ultrasonic generation, and optical heterodyne interferometry was us ed for detection of ultrasonic vibration on the specimen surface. Bond ed thin plates with character-shaped hallmarks with 1.5 mm width on bo nding layer were used as specimens. Imagings in ultrasonic transmissio n and reflection modes were performed, and imagings using not only XY- scanning of specimens but also a laser beam scanner were demonstrated. Ultrasonic images of hallmarks located 0.2 mm below the specimen surf ace were obtained through the experiments.