Study of the multilayer metallic films topography modified by laser interference irradiation

The thin bimetallic film systems Fe-Al, Fe-Ni, Ti-Al, and Ti-Ni were irradiated using a laser interference pattern with laser fluence values from 50 to 250 mJ/cm2. The thermal simulation was carried out to analyze the topographical effects. It was found that according to the laser fluence value, three different types of topographies can be obtained. For lower laser fluence values, the molten material in the lower layer induces deformation over the upper one obtaining a periodic pattern with a structure depth in the order of the layer thickness. If the laser fluence is high enough so that the upper layer reaches the melting point, this last is broken obtaining a high structured pattern consisting on a large depression and next two consecutive peaks. This threshold value can be estimated using the thermal simulation calculating the laser fluence at which the upper layer starts to melt. For higher laser fluence values, this pattern transforms into a periodical peak-valley structure with high structure depth. In both last two cases, the material at the interference peaks is removed. A model is suggested for explaining this behavior.