Anti-reflective (AR) coatings are indispensable for an excellent imaging of optical systems. Common AR coating systems consist of layer stacks of alternating low and high refractive index materials with the residual reflection depending mainly on the low refractive index (LRI) of the last layer relative to air. However, conventional LRI materials are limited to SiO2 (n = 1,46 at 532 nm) and MgF2 (n = 1,38 at 532 nm), where MgF2 is not environmentally stable. Nanostructures with an adjustable effective LRI in the range of 1.07 to 1.25 are an attractive alternative to these materials. Integrated as the last layer in the stack system, these structures significantly improve the optical performance compared to a conventional interference coating system, as a broadband AR coating can be realized, which is less sensitive to high angles of light incidence. Nanostructures can be produced using various methods - e.g. wet chemical or lithographic. However, these methods are expensive and time-consuming, as often more than one manufacturing step is necessary. At the Fraunhofer Institute IOF in Jena, self-assembling AR nanostructures have already been successfully fabricated for several years using a conventional plasma-ion-assisted-deposition (PIAD) technology. Thereby organic material is deposited on the substrate via thermal evaporation and subsequently self-assembling nanostructures are formed by an ion plasma source. Melamine and Uracil are already being used successfully as organic material. The advantage of this method is the generation of nanostructures in one process which is cost- and time-effective. In this talk, we want to introduce Xanthine, another organic material that is also highly promising for the generation of nanostructures exhibiting an LRI. We will demonstrate the formation of these nanostructures during plasma etching and investigate their optical performance for the use as an AR coating.
Transparent thermoplastic polymers are widely used as materials for precision optical lenses as well as for sensing and lighting. The advantages of transparent polymers for optical parts are significant weight reduction, high impact strength, molding options and cost saving mass-production. Antireflection (AR) coatings are essential to improve transmission and contrast of lenses, windows and display covers. Polymer-capable coating conditions must be investigated for each type of polymer because of the varying chemical and physical properties of optical polymers. A presently well-established coating technology for plastics is plasma ion-assisted deposition (Plasma-IAD). It enables the coating deposition at low temperature as well as low-energy plasma conditions and ion bombardment to tailor the optical and mechanical properties of oxide layers. A good understanding of complex interactions of polymer surfaces with plasma and high-energetic radiation is a key factor to achieve polymer optics with high-end AR-properties and long-time durability. The Aim of this study is to evaluate and to understand the surface properties of polymers which are relevant for the deposition of optical coatings and for its later application. The investigation is focused primarily on the new polymer types APEL, Iupizita EP and OKP. They are compared with the long-established materials such as polycarbonate (Makrolon) and ZeonexE48R. The optical properties of the polymers are systematically studied including the influence of aging caused by UV-irradiation, humidity and heat. In addition, properties like surface hardness, water absorption and thermal stability are compared and discussed. Different pre-treatments and designs are considered to bond multilayer AR systems to surfaces with high adhesive strength. In addition, plasma-etching technology AR-plas is applied to achieve AR properties for the visible spectral range (VIS).
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