Evaluation of fiber-reinforced composites using noncontact laser air- transducer system

Ultrasonic evaluation of materials using a non-contact system is sometimes desirable, for example when the material is moving too quickly to allow conventional fluid couplants to be used, is contained in a hostile environment, or the material itself is absorbent or toxic. In such situations, a pulsed laser is ideal for generating a variety of ultrasonic transients [1], as longitudinal, shear, surface (Rayleigh) waves and plate (Lamb) waves are generated simultaneously. Several types of non-contact detector are also available, including various optical devices [2] such as interferometers and beam deflectors. The disadvantages of an entirely laser based system are cost, and the optical quality of the test material must be reasonably high.