Measurements of S mode Lamb waves using a high-speed polarization camera to detect damage in transparent materials during non-contact excitation based on a laser-induced plasma shock wave

The demand for transparent materials has been expanding due to their ubiquity in products such as solar panels, tablet terminals, and smartphones. To mass produce high-quality products, quickly detecting damage on the µm scale and evaluating the quality are critical. Herein an Nd:YAG pulsed laser with a nanosecond order is used to generate a shock wave by laser induced plasma, which is subsequently used as a non-contact, non-destructive excitation force for transparent materials. Then, a high-speed polarization camera measures the generated Lamb wave. In this experiment, an impulse input is generated via a laser-induced plasma shock wave and the phase velocity of the generated Lamb wave in the polycarbonate plate is measured by a high-speed polarization camera. We found that this Lamb wave was in the S0 mode. Observing its propagation can detect scratches on the order of several hundred µm on the surface of a transparent plate in a non-contact, non-destructive manner.