Polarization effects in ultrashort-pulse laser drilling

A strong influence of the polarization of the laser radiation on the geometry of laser-machined microdrillings has been observed for ultrashort pulses. For drillings with a certain aspect ratio, reflections at the hole walls take place, leading to a non-uniform intensity distribution deep inside the formed hole. Experimental and theoretical results on this subject are discussed. It is shown that a rotation of the polarization during the drilling process (“polarization trepanning”) significantly improves the quality of the produced holes.