Laser ultrasonic and photoacoustic characterization of subsurface structures

Abstract

<p>There is a strong interest in applying laser ultrasonic and photoacoustic techniques to the NDE of some high performance structures, for example, the actively cooled panels of the National Aero-Space Plane. Both laser ultrasonic and photoacoustic techniques have been developed for years. Much significant work has been done on either the generation of waves, the mechanisms [1–3] or various techniques for the detection of these waves [4–6]. A few applications being pursued or conducted since the early stage of the development for these techniques [5–7]. However, there is little work concentrating on the interaction of these waves with structures and materials [8]. For successfully applying the laser ultrasonic and photoacoustic techniques to the NDE of a practical system, it is important to understand the interaction of laser generated ultrasounds and thermal waves with, for example, the subsurface structures or defects in the materials and their relationship to images obtained from the techniques.</p>