Acoustic microscopy for evaluating cracks produced by CO₂ laser within thin alumina plates

The laser shaping of thin alumina ceramic plates appears to be an advantageous manufacturing method. Unfortunately, the failure rate for using this technique is high because of crack initiation during the application of a high power laser. We address the issue of crack initiation with the use of in-process and post-process analysis. This article reports our results on the evaluation of the surface and interior cracks with optical, scanning laser, scanning electron and scanning acoustic microscopy. We present images of surface and subsurface micro-cracks generated at different power levels of a high power CO₂ laser system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that, some with improvement, the V(z) technique may detect residual stress with high spatial resolution. The obtained results may contribute to the understanding of the fracture mechanism, and can eventually provide guidance for the choice of laser parameters (e.g., power, focus, scanning rate, emitting duration, or the like) in laser shaping apparatus.