Specular transparent

Specular reflection of electromagnetic radiation at the (electrochemical) interface is generally described by Fresnel equations. Supposing the most simple case that both the electrolyte and electrode are transparent and differ only in their refractive indexes, nx and n2, the reflectivity for normal incidence of the radiation equals ... 

The spectrophotometer measures the transmission and, if an absorption measurement is carried out, converts the transmission into absorbance using these equations. This conversion works fine for samples where there is no reflection, either specular or diffuse, as is the case for nonturbid solutions. However, for films there is invariably some reflection, which is often quite large, particularly for films of high dielectric constant (or refractive index) materials, such as PbS and PbSe. Additionally, if the films are not completely transparent, then scattering introduces an extra element of reflection. Therefore, to measure the real absorption of a film, a reflection measurement must also be carried out and correction for this reflection made. The correction will be approximate and depends on the nature of the film itself. However, that most commonly used is... 

Specular Reflection. The specular reflection accessory can only be used with FTIR spectrometers. It permits the reflected light to be measured in a direction symmetrical to that of the incident beam (Fig. 10.19). This approach is mostly used for transparent samples which have a reflective surface (such as polymer films, enamel, certain coatings). 

Figure 6.29 The dichromatic reflection model assumes a matte reflection in combination with a specular reflection. Part of the light is reflected at the outer surface. The remainder enters the transparent coating. The second reflection is modeled as being Lambertian. (Reproduced by permission of Pearson Education from 3D Computer Graphics Third Edition, Alan Watt, Pearson Education Limited, Pearson Education Limited 2000.)...

As the reflected radiation is emitted from the sample in a random direction, diffusely reflected radiation can be separated from, potentially sensor-blinding, specular reflections. Common techniques are off-angle positioning of the sensor with respect to the position(s) of the illumination source(s) and the use of polarisation filters. Application restrictions apply to optically clear samples with little to no scattering centres, thin samples on an absorbing background and dark samples. In either of these cases, the intensity of radiation diffusely reflected off such samples is frequently insufficient for spectral analysis. While dark objectives remain a problem, thin and/or transparent samples can be measured in transmission or in transflectance. 

The substrates are coated with transparent electrodes (nesa or ITO) and often, but not always, with an appropriate alignment layer, usually a surfactant such as lecithin. A specularly reflecting mirror with a black background is fixed to the second substrate. No polarisers are required. Therefore, DSM-LCDs are intrinsically bright display devices with high contrast. 

Figure 28. Configurations for spectroelectrochemistry. A) optically transparent electrode B) optically transparent thin-layer electrode (OTTLE) C) Internal reflection spectroscopy, and D) specular reflectance spectroscopy.

Figure 44. Electrode systems for spectroelectrochemistry (a) optically transparent electrode, (b) electrode for internal reflection spectroscopy, and (c) electrode for specular reflectance spectroscopy.

There are three types of reflectance techniques specular, diffuse and reflection-absorption as illustrated in Figure 9.22. Specular reflectance is applied to samples with smooth and polished surfaces, diffuse reflectance is applied to samples with rough surfaces, and reflection-absorption is applied to IR-transparent thin films on IR opaque substrates. The specular and diffuse techniques are more widely used and are introduced in more detail in the following text. 

Mica-Lyte, Dekorflake, Microfibers, Specular - selected natural, colored, and shaped materials designed as special-effect colorants to impart granite-hke, sparkling, and textured appearances to transparent and translucent polymers... 

XXXVI, 46 ..in Cappadocia, one finds a st one with the hardness of marble and white and transparent. .. which on the basis of these characteristics has been called phengite the temple of Fortune was built with this stone.. .. Thanks to the stone, even with the doors closed, there was light inside as if during the day, but the effect was different from that with specular stone it seemed as if the light was not transmitted from the outside but was enclosed within. ... 

A number of transparent polymers have been examined and tested for this purpose prototype domes have been fabricated from polyvlnylfluorlde which was later determined to be too expensive and not sufficiently stable. The dominant requirement for this application Is good specular transmission. Several polyesters... 

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