Study of Through-Hole Micro-Drilling in Sapphire by Means of Pulsed Bessel Beams

Ultrashort Bessel beams have been used in this work to study the response of a 430-mu m-thick monocrystalline sapphire sample to laser-matter interaction when injecting the beam orthogonally through the whole sample thickness. We show that with a 12 degrees Bessel beam cone angle, we are able to internally modify the material and generate tailorable elongated microstructures while preventing the formation of surface cracks, even in the picosecond regime, contrary to what was previously reported in the literature. On the other hand, by means of Bessel beam machining combined with a trepanning technique where very high energy pulses are needed, we were able to generate 100 mu m diameter through-holes, eventually with negligible cracks and very low taper angles thanks to an optimization achieved by using a 60-mu m-thick layer of Kapton Polyimide removable tape.