Refraction index, substrate material

Despite the gains in internal quantum efficiency, the overall efficiency is still less than 19%. As much as 80% of the photons produced cannot get out because of the high index of refraction of the polymer material. Approaches such as texturing the surface of the glass, index matching or using low index substrate materials, and the use of arrays of microlenses have made increases in the extraction efficiency. 

We are now in a position to calculate the reflections from multiple mterfaces using the simple example of a thin film of material of thickness d with refractive index n.2 sandwiched between a material of refractive index (where this is generally air witii n = ) deposited onto a substrate of refractive index [35, 36], This is depicted in figure Bl.26.9. The resulting reflectivities for p- and s-polarized light respectively are given by ... 

Ellipsometry is a method of measuring the film thickness, refractive index, and extinction coefficient of single films, layer stacks, and substrate materials with very high sensitivity. Rough surfaces, interfaces, material gradients and mixtures of different materials can be analyzed. 

The refractive index of a film or a substrate material can be measured with a sensitivity better than 5 x 10, the best available for non-invasive optical measurement methods, especially for thin films. The extinction coefficient can be measured with almost the same sensitivity, which corresponds to a lower limit of 10-100 cm for the absorption coefficient of the material. 

What is a coating on a substrate It is a thin layer, of a stack of thin layers, made of materials with a refraction index different from that of the substrate. Part of the light is reflected at each interface between the layers or between air and the first layer or between the last one and the substrate. Reflected beams interfere so that for a given wavelength and a given thickness, reflected light can be either canceled out or maximized. It corresponds to maximum transmission or reflectivity of the layer respectively. These materials and their indexes are chosen in order to fit as close as possible the specifications for the final coated optics. 

The role of the substrate temperature can be inferred from a plot of /J2 ev and R versus max at the three temperatures mentioned 200, 250, and 300°C (see Figure 49). At a substrate temperature of 200°C the refractive index is lower at every max than at a substrate temperature of 250°C. Further, the threshold at which dense material is obtained is observed to be a few electron volts higher than at 250°C. The refractive index at 300°C is high and independent of max-The microstructure parameter R as a function of max behaves similarly for material deposited at 200 and at 250°C. At 300°C the value of R is less than 0.1 and independent of max- It is noteworthy to show the relation between the internal stress and max as a function of temperature (Fig. 50). The stress is linearly... 

One possibility to obtain a relatively small leakage into the substrate is to introduce a thin film of metal or absorbing layer such as a polymer or a dye with a complex dielectric function, or a thin layer of low refractive index material... 

The dependence of PS porosity on doping density has been exploited to fabricate optical waveguides. Such structures require only a single variation of refractive index. If a p-type substrate with implanted p+ lines is anodized and partially oxidized, mesoporous lines of high refractive index are embedded in a low refractive index material. An obtained refractive index contrast between core and clad of 30% is promising for future applications [Tal2]. 

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