High refractive index optical coatings

Another technique that is important for optical immunosensor development is internal or attenuated total reflection spectroscopy (Fig. 126). A waveguide (slide or fiber) having a high refractive index is coated with a layer of immobilized antibody. The incident light... 

A flexible optical fiber has a high-refractive-index, transparent core enclosed in a lower-refractive-index, transparent cladding (Figure 20-18a). The cladding is enclosed in a protective plastic jacket. The core and the coating can be made from glass or polymer. 

U.S. production of methyl methacrylate in 1999 totaled 1.4 billion lb, which is about 82 percent of world capacity. Its uses are almost exclusively based on polymerization to poly(methyl methacrylate), which, because of its physical strength, weathering resistance, optical clarity, and high refractive index, has major uses in cast and extruded sheet (33%), molding powders and resins (16%), and surface coatings (22%). 

In general, polyimides exhibit a high refractive index typically between 1.6 and 1.7 and hence can be of definite practical interest particularly as antireflection coatings. Also, similar to parylene thin films, polyimides exhibit anisotropic optical properties. The reported values of refractive index of polyimides were n = 1.653 and n = 1.624 before curing and... 

Cyclohexylacrylate gives a polymer for optical lens, coating, good contacting, and high refractive index ... 

Low indexes of refraction tend to reduce surface or back reflection and are desirable for certain applications such as antiglare coatings. High indexes of refraction tend to correspond to higher part brilliance and thinner optical lenses for a given distance. A high refractive index makes a plastic useful for optical components. Polystyrene has a relatively high refractive index (1.60), and polytetrafluoroethylene has a relatively low refractive index (1.375). 

Dielectric used in film supercapacitors. Tantalum oxide is a high-refractive index, low-absorption material usable for making optical coatings from the near-UV (350 nm) to the IR (8 p.m). Insoluble in most chemicals except HF, HF—HNO3 mixtures, oleum, fused alkaU metal hydroxides (e.g. NaOH and KOH) and molten pyrosulfates. Tantalum pentoxide (tantalite, tantala)... 

Oxides of transition metals, such as niobium, tantalum, or titanium, are suitable as waveguiding layers on optical (grating coupler) waveguides due to their high refractive index and transparency. Therefore, oxide-coated chips are used as sensing devices in technology based on the interaction of a laser-induced evanescent field with analyte constituents adsorbed on or immobilized at the waveguide/ fluid interface. ... 

Waveguides consist of a thin layer of a high-refractive index material surrounded by/embedded in a low-refractive material. One way of making these layers uses of photolocking of a second component in a polymeric layer, followed by removal of this component from the unexposed area In this way, fiber optic sheet systems have been made as well as beam splitters, couplers, etc. In a typical example (Fig. 13) a dilute solution of polycarbonate, methyl acrylate and a photoinitiator in a solvent is spin-coated on a substrate, pattemwise exposed such that the methyl acrylate polymerizes in the exposed area and finally evaporation of unreacted monomer from the unexposed areas. 

More recently, ZnS-coated PS nanocomposite colloids were synthesized by the chemical bath deposition technique of thioacetamide in the presence of PS seed particles and metal salt [197], It allowed deposition of high refractive index ZnS shells of controlled thickness onto sulfate-modified and plain PS cores of size of about 200-500 nm. In order to prevent aggregations of PS particles, PVP was added during the reaction. The effective refractive index of the ZnS shell-PS core (PS/ZnS) composite particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. The porosity of the shells was between 12 and 19%, and the core-shell colloids served as building blocks for self-assembly at the submicron length scale [197]. 

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