High-speed machining of sapphire using transient and selective laser (TSL) processing

Sapphire is a promising material for advanced optical and sensing devices because of its excellent hardness, thermal conductivity, and transparency. The Bessel TSL (Transient and Selective Laser) processing method enables ultra-highspeed micromachining of transparent materials by combining an ultrashort laser pulse that forms a filament with a microsecond pulse that is selectively absorbed within the filament to induce ablation. In this study, we applied this method to sapphire and investigated its machining behavior using high-speed imaging. A filament penetrating a substrate with a thickness of several hundred micrometers was generated using a 1030 nm, 5 ps laser, followed by selective absorption induced by a 1070 nm microsecond laser. Experimental results showed material removal from both surfaces at a rate of approximately 0.5 μm/μs, which is about 500 times faster than conventional picosecond-laser machining. In addition, for a 500 μm-thick sapphire sample, we also succeeded in selectively heating an ultra-high-aspect-ratio region. These results demonstrate the strong potential of Bessel TSL processing for ultra-high-speed sapphire micromachining.