Laser-induced incubation in transparent materials and possible consequences for surface and bulk micro-structuring with ultra short pulses

We performed surface and bulk processing experiments on different transparent materials with ultra short laser pulses. The investigations were performed mainly at 800 nm and at pulse widths ranging from 0.2 to 5 ps. We focused our attention on fluence and shot number dependencies to analyse possible incubation effects in the different materials and determine the damage threshold. In the multi-shot experiments we determined strong incubation effects which we attribute to laser-induced defect formation and accumulation. Inside the bulk we were able to generate dots and lines even in sub-mum sizes. The structures were analysed by means of optical microscopy. Laser pulses at a pulse width above ca. 1 ps demonstrate strong self focusing which can be utilized for bulk and rear surface micro structuring. Below a certain pulse width other effects counteract self focusing and beam diffraction and fillamentation seem to dominate. Depending on focusing optics we observe strong differences in the possibility to process the bulk of transparent materials with fs laser pulses which we attribute to the effects in Kerr non-linearity. Also, the consequences of incubation effects on the structuring inside the bulk seem to depend strongly on the pulse width. We discuss the results based on possible technological relevance and the ablation mechanism involved.