Direct micro-structuring of Si(111) surfaces through nanosecond laser Bessel beams

We present a nanosecond laser ablation of Si(111) surfaces with diffraction-free (Bessel J(0)) beams. Experimental results compared with theoretical predictions show that Bessel beams give possibility of straightforward micro-structuring of Si(111). Only central spot could damage the surface provided that the laser pulse energy is in the energy range we confirmed in our experiments. Moreover, our results clearly indicate that reduced heat-affected zone area due to thermal expansion in ns pulse regime is natural outcome of Bessel beams as opposed to Gaussian beams. This method is open to be improved by using high-quality Gaussian beams (M-2 approximate to 1) while the size of structures can be much reduced by using larger base angle of the Axicon (such as alpha = 40 degrees).