Calculating the Borehole Geometry Produced by Helical Drilling with Ultrashort Laser Pulses

Laser drilling is a processing technology applicable for creating holes in various materials. By combining an ultrashort pulsed laser with a helical drilling optics, it is possible to produce high-quality holes with sharp, burr-free edges in a large variety of borehole geometries. To master this highly flexible process which is determined by a multitude of variables, a mathematical description of the problem is advantageous. A simulation model is presented for calculating the final borehole geometry for a given set of laser, process, and material parameters. The model was validated by comparison to boreholes drilled into four different materials: stainless steel, copper, silicon, and aluminum oxide ceramic. By inserting literature values for the refractive index and the ablation threshold fluence, a good agreement between model and experiment can be achieved for holes of different shape and size.