Detection of flaws on metal surfaces using tone burst laser ultrasound

Metal surface flaws on can be detected using the frequency transmission characteristics of surface acoustic waves (SAW). In addition, noncontact, remote detection can be made possible by using laser ultrasound. So far, broadband SAW generated by a single generation laser has been used for surface flaw detection[1]. Results have shown that the SAW transmitted across a slit of depth 0.5 mm showed a large decrease in frequency components over 1 MHz. Higher frequencies are needed to detect shallower slits, but the frequency spectrum of SAW generated by a single generation laser cannot be controlled. As a consequence, SAW of higher frequencies could not be selectively generated, and detection of shallower slits has not been difficult. The frequency of SAW can be controlled by using tone burst SAW, which can be generated using multiple generation lasers[2]. In this research, tone burst SAW generated using 8 lasers is used for detection of artificial slits on metal specimens.