High-refractive-index materials

Attenuated Total Reflection (ATR).4c A sample brought in contact with the totally reflecting surface of a high-refractive-index material (the ATR crystal), will, on IR irradiation, give an evanescent wave in the less dense medium that extends beyond the reflecting interface. This wave will be attenuated in regions of the IR spectrum where the sample absorbs energy. Observation of such waves constitute ATR measurements. Only the small amounts of beads necessary to cover the area of the ATR crystal are required. 

High-refractive-index materials enable the investigation of bioreactions at the surface within the evanescent field. Various sensor systems were developed with the advantage of high sensitivity and measurement in the presence of the sample without any rinsing. The sensor principles can be divided into label-free sensor systems where the determination of the effective refractive index is the pivotal parameter and systems based on surface-confined fluorescence excitation where the marker molecule is solely detected. 

Figure 5 illustrates the Augff of waveguide modes of different high refractive index materials for different modes and polarizations. The quantity Aweff is plotted... 

Closely related to the salt infiltration method discussed above is the utilization of metal alkoxide precursors in a sol-gel process to fill the interstitial sites in an opal template. The template is first infiltrated with an alkoxide (neat or as solution), then the hydrolysis and condensation reaction following the infiltration transforms the alkoxides into an extended network of the corresponding metal oxide. By this method Ti02 networks besides other oxides were initially prepared with a strong focus on their optical properties as photonic crystals [30,50]. For this purpose a high refractive index material is desired, which would be the rutile modification of titania with the highest refractive index. Nevertheless, the sol-gel procedure provides an amorphous or anatase modification with lower refractive index. By calcination of the anatase... 

The attenuation of a beam of radiation passing through an optical element from a high refractive index material, under the condition of total internal reflection, is measured. The sample must be in good optical contact with the surface of the optical element at which total internal reflection occurs. 

Grating fill factor Fraction of the grating period occupied by the high-refractive-index material, tin. 

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. 

Be aware that cells made from nontraditional window materials, such as zinc selenide, zinc sulfide, germanium, or other medium to high refractive index materials, will usually result in the production of interference fringes, even in the presence of the sample. 

Nussbaumer J, Caseri WR, Smith P, Tervoort T (2003) Polymer-Ti02 nanocomposites a route towards visually transparent broadband UV filters and high refractive index materials. Macromol Mater Eng 288(l) 44-49... 

Attenuated Total Reflection Measurements 183 Table 13.1 High refractive-index materials used for the internal reflection element (IRE)... 

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