Saturation of ablation channels micro-machined in fused silica with many femtosecond laser pulses

We investigate the effect of saturation in the propagation of ablation channels performed in fused silica with many incident femtosecond pulses and laser fluence slightly above the ultrafast ablation threshold. A 110 fs Ti:Sapphire laser system is used in the experiments and the results are compared with theoretical predictions performed with a numerical model developed by the authors. Diffraction of the incoming pulses at the entrance of the channel as well as reflections at the walls of the channel play a crucial role in the progress of the crater as it is shown by means of the numerical results. The effect of the pulse duration in the shape of the ablation channel is also investigated.