The effect of laser wavelength on the efficiency of laser-generated ultrasound for the inspection of CFRCs

The aim of the present work is to obtain a further understanding of the laser generation of ultrasound in carbon fibre-reinforced composites (CFRCs) for non-destructive testing. Three different laser wavelengths have been used for the ultrasonic generation: 10.6 μm (TEA CO₂), 1.064 μm Nd:YAG) and 308 nm (XeCl excimer). The ultrasonic generation mechanism in materials such as CFRCs is determined by the optical absorption depth of the superficial resin layer and the underlying layers of carbon fibres, which is mutually dependent on the material characteristics and laser wavelength. Comparative results of generation efficiency between the three wavelengths used are presented and the role that the resin matrix plays is evaluated.