PMMA Optical Diffusers with Hierarchical Surface Structures Imprinted by Hot Embossing of Laser-Textured Stainless Steel

Abstract

Increasingly compact and powerful light emitting diodes require the development of efficient optical diffusers to manage their lighting capability according to the required application. In this study, a cost-effective strategy is demonstrated for fabricating micro-structured polymethylmethacrylate (PMMA) diffusers for white light sources. By combining different laser-based processes, namely direct laser engraving (DLE), direct laser writing (DLW), and direct laser interference patterning (DLIP), periodic patterns are fabricated in stainless steel surfaces with line- and dot-like geometries with feature sizes ranging from 1.7 to 900 µm. The fabricated hierarchical geometries are transferred to PMMA surfaces by plate-to-plate hot embossing. The relationship between the surface topography and the white light scattering behavior is investigated by confocal and scanning electron microscopy combined with photospectroscopy and image processing of photographs. The triple-scaled hierarchical structures can increase the haze up to 76% in the visible spectrum, while keeping the total transmittance over 90%, as the flat surface.