Crater drilling enhancement obtained in parallel non-collinear double-pulse laser ablation

In order to investigate the double-pulse ablation mechanism, two parallel but non-collinear laser beams, delayed with respect to each other by 1 mu s, were focussed on an aluminium sample, so that a lateral distance of 600 microns exists between the centres of the two craters and no superposition of the laser-ablation zones is present. The use of such configuration results in a signal and in a plasma mass enhancement with respect to the single-pulse case almost equal to that obtained in the double-pulse collinear case. However, such a non-collinear geometry evidences a much more effective drilling of the surface. Such unexpected drilling seems to be related to a hydrodynamic drainage out of aerosol and molten material, hindering its re-deposition in and around the crater.