Picosecond pulsed laser ablation of dielectric rods: Angle-dependent ablation process model for laser micromachining

The ablation of fused silica and sapphire is investigated from the perspective of laser micromachining. In this study, dielectric rods are machined using a 12 ps pulsed laser at 1064 nm wavelength. The machining of the rods is a calibration method to determine process parameters for an analytical ablation model. More specifically, the ablation threshold fluence and effective penetration depth are determined under process-relevant conditions due to the removal of macroscopic volumes, which leads to a higher accordance. The introduced ablation model predicts macroscopic ablation volumes and ablation efficiencies of dielectric materials as a function of the angle of incidence. Originally, the ablation process model was developed for metals under the normal incidence, but this work extends its applicability to dielectrics. In contrast to metals, the optical penetration depth should be independent of the angle of incidence. Altogether, the presented model is universally applicable and can be seen as a first step toward computer-aided 3D-manufacturing using ultrashort pulsed lasers. The ability to predict ablation volumes and machine heat-sensitive tool materials with high accuracy and precision is demonstrated by the fabrication of end mills made of fused silica and sapphire with a diameter of 1 mm. This shows that picosecond lasers are well suited for the fabrication of such microcutting tools. In particular, the ability of ultrashort pulses to ablate materials independent of their hardness and without any wear makes this technology highly promising for the tooling industry.