Single-shot ablation of sapphire by ultrashort laser pulses

Abstract

Single-shot laser ablation of single-crystal sapphire (0001) samples by ultrashort infra-red laser pulses has been undertaken. The laser-generated structures are analyzed by scanning-electron and atomic-force microscopy. The data produce an ablation threshold of 8.4±0.6 J/cm2 ((8±2)⋅1013 W/cm2) for a pulse duration of 100 fs. The observed features are compared to detailed numerical simulations based on a multiple-rate equation description of the electronic excitation by strong-field and collisional-impact excitation. The comparison shows that both the threshold and the ablation rate versus fluence is reproduced with good accuracy by the calculation, provided ablation is assumed to occur when the excitation exceeds ∼10% of the valence-electron density.