OVERVIEW: ULTRASOUND SENSING USING GAS-COUPLED LASER ACOUSTIC DETECTION

Abstract A novel laser-based technique for the detection of ultrasound radiated from solid materials has been developed. In this approach, a probe beam is directed parallel to the surface of a sample. Ultrasonic waves in the solid are detected when an acoustic wave is radiated from the surface into the ambient air where the density variations cause a beam deflection. Because the detection laser beam is not reflected from the sample surface. the technique is not dependent upon the surface optical properties of the material under investigation. It is particularly useful for testing materials with poorly reflecting surfaces such as graphite/polymer composites. Gascoupled laser acoustic detection (OCLAD) has been used to record well-resolved throughtransmission, Rayleigh, and Lamb waves in various materials. GCLAD has also been incorporated into a C-scanning system where it has been used to image subsurface flaws in graphite/polymer composite panels.