High-speed observation of damage generation during ultrashort pulse laser drilling of wide-bandgap materials

Many materials with wide bandgap, such as glasses, sapphire, and silicon carbide (SiC), have excellent optical, electrical, and mechanical properties and are used in various industrial and scientific applications. Ultrashort pulse laser processing has been attracting attention as a method of micromachining wide-bandgap materials. Because the peak intensity of ultrashort pulse laser is extremely high, its focused pulse can make wide-bandgap materials absorb its light energy via multiphoton absorption. However, it has a problem that damage occurs around the processed region. In this study, we observe the high-speed phenomena during the ultrashort pulse laser drilling of wide-bandgap materials using pump-probe imaging in combination with a high-speed camera to clarify the mechanism of damage generation. This method visualizes both the static phenomena such as the processed shape and the damage, and the dynamic phenomena such as the electron excitation and the stress wave propagation, which change with each pulse irradiation. In addition, we conduct the experiments by changing the pulse width and the material to be processed to investigate the dependence of damage generation on the processing condition. The results show that stress waves propagating inside the material during processing cause the damage, and that the damage generation pattern changes depending on the pulse width and material. This study contributes to optimizing the processing conditions to suppress the damage during the ultrashort pulse laser processing of wide-bandgap materials.