Crystallographic dependence of ultrafast laser induced crack generation in single-crystal sapphire

Crack generation is a bottleneck in the processing of sapphire crystals using ultrafast laser. This paper aims to investigate the influence of crystal orientation on the laser-induced crack generation in single-crystal sapphire at the atomic scale. A molecular dynamics model of sapphire crystal irradiated by ultrafast laser was constructed, and the influence of crystal orientation on atomic number density and pressure was analyzed. The results show that smaller interplanar spacing enhances the material's resistance to damage, resulting in a faster stabilization rate of atomic number density within the crystal. The relationship among stress wave propagation speed, interplanar spacing and the direction of crack initiation in sapphire crystals was explored. It was found that crystal orientations with lower stress wave propagation speeds are more prone to crack generation. Laser induced sapphire crystal crack generation experiments were conducted, and the results showed that cracks were most likely to occur along the (10-10) direction, followed by the (01-01) direction, and the (1–100) direction exhibited the least susceptibility when laser irradiation on the C-plane of sapphire crystals. The research of this article will provide theoretical and technological guidance for suppressing the generation of laser-induced cracks in sapphire crystals.