LASER-BASED NON-DESTRUCTIVE TESTING TECHNIQUES FOR THE ULTRASONIC CHARACTERIZATION OF SUBSURFACE FLAWS

Abstract Laser generation and detection of ultrasound has been used for remote characterization of flat-bottomed holes, acting as subsurface flaws, drilled into an aluminium test sample. A pulsed Nd:YAG laser system was used to generate the ultrasonic source whilst a HeNe laser interferometer detected the subsequent surface displacements. The technique allows both the width and depth of flawa to be assessed. Moreover, an analysis of the data shows that the method is particularly suited to detection of flaws ≤ 4 mm below the surface of the sample, a region which is difficult to inspect by conventional contact ultrasonic techniques.