LASER-INDUCED FORWARD TRANSFER OF ALUMINUM

The laser-induced forward transfer (LIFT) of aluminium is experimentally investigated for aluminium target thicknesses up to some mu-m. The aluminium is transferred to glazed ceramics and to silicon substrates with and without oxidized surface, respectively. Two types of laser beam sources are used: a Nd:YAG laser with a Gaussian beam profile and a Nd:glass laser system providing a homogenized flat top profile. The resulting deposition is determined by the removal mode of the Al from the target and by the interaction of the molten Al with the substrate. In a first removal mode (low laser intensities and/or thin targets) where melting through of the target precedes the onset of vaporization at the target front side the material can easily be transferred to the substrate. In a second mode (high laser intensities and/or thick targets) the blow-off process is characterized by higher vapor pressures which leads to disturbed deposits. The interaction of impacting material with the substrate causes the formation of droplets on oxidized surfaces due to the high surface tension of liquid metals.