A FIBRE-OPTIC DETECTION SYSTEM FOR LASER-ULTRASOUND LAMB-WAVE EXAMINATION OF DEFECTS IN THIN MATERIALS

Abstract

Laser-generated ultrasonic Lamb waves have been measured in metallic thin films with a novel fibre-optic beam deflection technique. Instrumentation consisted of a flexible fibre-optic sensor used for the detection of thermoelastically-generated Rayleigh and Lamb waves. It used a single mode fibre which delivered a 14 mW probe beam onto the sample surface. Angular perturbations of the reflected beam due to ultrasonic transient were monitored using a fibre-optic bundle incorporating differential photodetection. Results acquired by the optical fibre sensor have examined small artificial notches machined into samples. They show that the non-contact optical systems can detect 10 μm deep defects in a 125 μm thick plate on a single shot basis.

keywords:

• Laser ultrasound
• lamb waves
• non-destructive testing
• optical inspection
• fibre optics
• defects