Investigation on single-pulse 266 nm nanosecond laser and 780 nm femtosecond laser ablation of sapphire

Investigation on single-pulse 266 nm nanosecond laser and 780 nm femtosecond laser ablation of sapphire was carried out. Diameter, depth and volume of ablated holes varying with laser density is studied. The results show that 266 nm nanosecond laser ablation of sapphire is caused by photochemical and photothermal effects. 780 nm femtosecond laser ablation of sapphire is due to "cooling"ablation. As energy density increases, thermal effect still exists, yet being much less significant, while ablation mass is greater than that by nanosecond laser. In nanosecond and femtosecond laser ablation, the ablation efficiency increase first and then decrease due to plasma shielding. Ablation efficiency is higher by nanosecond laser than by femtosecond laser at the same laser density. The ablation efficiency reaches the maximum at the energy density of 55.32 J/cm2 to 68.43J/cm2. However, 780 nm femtosecond laser could machine a microstructure with larger depth diameter ratio at lower density.