Crack detection with Gas-Coupled Laser Acoustic Detection technique

The Gas-Coupled Laser Acoustic Detection (GCLAD) is an unestablished ultrasonic detection technique, based on the displacement that a laser beam sustains when intersected by an acoustic wave travelling inside a fluid. In the present work, the GCLAD for non-contact detection of ultrasound is applied to identify surface defects on metal plates. Two GCLAD configurations are analysed, associated with different sensitivity to cracks; specifically, the GCLAD exhibits the highest sensitivity when inclined perpendicularly to the ultrasonic propagation direction in the air. The high angular selectivity allows evidencing only specific waves, directly travelling in the component or reflected by defects. Higher ultrasonic amplitude is highlighted for the GCLAD compared to air-coupled probes. The work ultimately demonstrates the GCLAD major advantage: the possibility to instantly perform inspection over an entire line, rather than on a point as for traditional transducers.