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Structural colors can be induced on metals not only to fabricate logos or decorative motives but also to embed anti-counterfeit features for product protection. In this study, stainless steel (EN 1.4301) plates are colorized by growing a thin oxide layer using direct laser writing (DLW) and hidden anti-counterfeit measures are included on their surfaces by direct laser interference patterning (DLIP) processing. The periodic microstructures resulting from the DLIP treatment have a spatial period of 1 µm and act as relief diffraction gratings, featuring a characteristic diffraction pattern. These microstructures are not visible to the human eye but are easily detectable upon shining a coherent beam on the surface. Furthermore, the reflectance over the visible spectrum of the colorized surfaces with and without the DLIP microtexture is measured, giving low differences in the color perception following the so-called “CIE L*a*b*” color space. Finally, a demonstrator is fabricated, in which colorized fields with and without the security features are shown.

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 geom-etries 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.

Functionalized surfaces can be obtained by fabricating deterministic or stochastic structures with features in the micrometer, submicrometer and nanometer range. However, significantly enhanced surface properties can be produced by using micrometer scaled features covered by nano- or sub-micrometer structures, which occurs typically in natural examples [1] .

Hierarchical textures are researched experimentally and by optical simulations in the role of external outcoupling solution for OLEDs. Their full outcoupling potential, limiting factors and pathways for further increase in outcoupling are addressed.

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.

Porous fiber structures are of great concern to many fields of life-science engineering, but require a complex assembly processes that have geometric constraints. For this reason, tremendous efforts were expended in recent years to develop micro-/nano fabrication techniques. We report on the 3D structuring of a 3.5 mm long branched hollow fiber with 150 μm outer diameter and predefined circular pores (diameter: 30 μm). The investigated process is based on two-photon polymerization (2PP) of the UV curing resin OrmoComp®. The incident light of a femtosecond pulsed laser at 790 nm wavelength is used to generate the structure. Utilizing the non-linear behavior of two-photon absorption due to a tightly focused, high-intensity laser beam allows the local fabrication of three-dimensional structures in the photoresist. Voxels fabricated by 2PP are studied by controlling average laser power and exposure time. The appropriate average pulse energy and writing speed are determined to apply the optimal exposure parameters concerning the geometric accuracy and overall quality of the structure. The 2PP direct laser writing process is employed to generate the hollow fiber at an average laser power of 105 mW, and a writing speed of 5.0 mm/s. Water flowing through the fiber provides evidence that the core is hollow.