Fabrication of hierarchical micro patterns on PET substrates using direct laser interference patterning

Hierarchical microstructures offer improved surface functionalities or a combination of surface properties compared to single-scale patterns, e.g., low reflectivity and hydrophobicity. The fabrication of three-level length-scales microstructures on polyethylene terephthalate(PET) substrates is demonstrated using UV nanosecond-pulsed direct laser interference patterning. The 1st level is created by an array with 10mm spatial period. The 2nd level results from the interference within a holographic pixel (1-2mm spatial periods), while the 3rd level is related to the pixel distance (35mm). The effect of the laser fluence on the structure quality and depth is investigated. Finally, optical properties of the produced multiscale patterns are determined and compared to numerical calculations.