Adaption of Energy Deposition in Helical Drilling of Multidimensional Micro Holes Using Ultrashort Laser Pulses

High-precision, multidimensional holes are required in many technical applications. Due to its undercut shape, these kind of holes are usually manufactured from two sides of the work piece including a time-consuming co-axial alignment. Compared to current state of the art, a one-sided drilling strategy has numerous advantages regarding flexibility, precision and process efficiency. In this work, a helical drilling optic and an ultrashort pulse laser are utilized to fabricate a rotationally symmetric multidimensional-shaped hole in one single process step. The influences of single pulse energy, pulse repetition rate, rotation speed of laser beam as well as the drilling time on ablation depth are investigated. By varying the pulse energy and pulse density, the deposited energy per unit length on the single helical path can be adapted and thus the ablation depth can be scaled. With the adapted laser energy deposition, a T-shaped hole with a uniformed depth of about 80 mu m inlet is fabricated. Morphological analysis on the hole wall show excellent drilling quality without recast layers or heat-affected zones and roughness Rq < 0.35 mu m.