High-speed observation of damage generation during ultrashort pulse laser drilling of sapphire

Abstract

Ultrashort pulse laser processing attracts attention as a microfabrication method for transparent materials such as sapphire. However, during processing, numerous damages are formed around the processed area, which inhibits precision processing. In this study, to elucidate the damage generation mechanism, we combined a pump–probe imaging method with a high-speed camera and investigated the relationship between high-speed phenomena during processing and damage generation. Using the imaging system, a simultaneous observation of ultrafast phenomena on a timescale of picoseconds to nanoseconds and relatively slow phenomena on a timescale of milliseconds was achieved with a high spatial resolution, and the results clarify that stress wave propagation caused damage generation. In addition, the results showed that as the number of pulses increased, both positions of the stress wave generation and damage generation changed. Furthermore, we evaluated the pulse width dependence and demonstrated that the heat affected the damage generation when the pulse width was long. The damage generation mechanism clarified in this study will contribute to the development of methods for the precision processing of sapphire.