Abstract
Laser techniques are beginning to be used for noncontact ultrasonic inspection of carbon fibre reinforced composites in industry. The ultrasound is normally generated with a high-power pulsed laser and is detected with a laser interferometer. Other non-contact detection methods can also be used, such as simpler laser beam deflection techniques and air coupled transducers. The authors compare the generation efficiency and damage thresholds of a fundamental Nd:YAG laser (1.06 /spl mu/m), and a TEA CO/sub 2/ laser (10.6 /spl mu/m) which is normally preferred for carbon-fibre reinforced composites). A Nd:YAG laser with an optical parametric oscillator (OPO) tunable up to 4 /spl mu/m is also examined. The laser energy is absorbed within the optical absorption depth; the temperature rise is affected by the wavelength and laser pulse duration. It is essential to remain in the thermoelastic regime in order not to damage the material. A modified Michelson interferometer is used to detect the absolute displacement of the ultrasound. Optical beam deflection techniques and air-coupled transducers are also evaluated as detectors.
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