Observation of different mass removal regimes during the laser ablation of an aluminium target in air

The mass removal mechanisms occurring during the ablation of an aluminium target, induced by a Nd:YAG laser at lambda = 1064 nm in air, were investigated in the fluence range between 1.5 and 840 J cm(-2). The spectroscopic analysis of the plasma emission allowed the calculation of the plasma thermodynamic parameters and an estimation of its atomized mass. Conversely, microscopic analysis of the craters allowed the calculation of the hole volume and the quantification of the material accumulated in the rim around it, as well as a qualitative inspection of the craters profile and appearance. The trends of line intensity, of the atomized plasma mass and of the crater volumes with laser fluence suggest the identification of four laser fluence ranges, where a different role of background gas is played and different mass removal mechanisms seem to occur. A complex picture is drawn where vaporization, melt displacement, melt expulsion and phase explosion take place at different laser fluences.