The formation of convex microstructures by laser irradiation of dual-layer polymethylmethacrylate (PMMA)

This work presents the fabrication of convex structures by laser irradiation on dual-layer polymethylmethacrylate (PMMA). The surface PMMA layer can prevent gaseous product from escaping and the high absorption of underlying black PMMA layer can ensure enough gas products produced. It is shown that convex structures can only be formed in a particular focus range. The focus position range for appearance of convex structures is determined in our experiments to be 180-400 μm. And then the dependences of height and diameter of convex structures on pulse energy, pulse number and film thickness of surface layer have been investigated. The result demonstrates that the size (both diameter and height) of convex structures could be tuned by pulse energy; compared with the diameter, the height of convex structures is more sensitive to pulse number and film thickness of surface transparent layer. The formation of convex structures is attributed to the sensitively balanced combination effect between the softening of surface material and expansion of underlying material. Finally, large-area-arrays of convex structures with high consistency and variable tunable sizes were generated. The diameter and height of convex structures were measured to be 149 μm and 43 μm, respectively.