Precision laser microdrilling of sapphire via reducing transient pressure

Ultrafast lasers are used for micromachining transparent hard and brittle materials, but cracks and damage are challenges. Here, we demonstrate precision microdrilling in sapphire through temporally shaping ultrafast laser pulses. The strategy aims to suppress transient strong pressure in processing regions by minimizing direct laser absorption by materials. The shaped pulse has an initial ultrafast spike for electron excitations, followed by a flat tail having subnanosecond width for plasma heating. The plasma absorbs laser energy during its expansion and simultaneously ablates materials, weakening transient stress wave and pressure, avoiding cracks and damage. High-quality microholes are fabricated by multiple shaped pulses.