Influence of Pulse Duration on High-Precision Manufacturing of 3D Geometries

We report on the evaluation of different pulse durations between 230 fs and 5 ps on the layer-wise ablation of fused silica. In an initial step, the polished samples are roughened by scanning the laser across the surface and ablating hatches consisting of parallel lines, where chipping and cracking is present for longer pulse durations. The ablation behavior of the further layers showed two ablation regimens with respect to the laser fluence for all pulse durations. Furthermore, for longer pulses a more efficient ablation process is found. With increasing pulse duration, the surface roughness is increased, an undesirable effect for high-precision micromachining. To demonstrate our micromachining process, we defined 3D geometries, i.e., axicon, spherical and cylindrical lenses which are ablated with 230 fs by layer-wise removal of the silica. Laser scanning microscope images show the effective fabrication of the 3D objects. Cross-sections reveal excellent agreement between the designed and the experimentally fabricated geometries confirming our high-precision micromachining process.