Measured Optical Properties

The transmittance spectrum of a titania nanotube-film (transparent) on glass is shown in Fig. 5.33. The optical behavior of the Ti02 nanotube-arrays is quite similar to that reported for mesostructured titanium dioxide [133], The difference in the envelope-magnitude encompassing the interference fringe maxima and minima is relatively small compared to that observed in titania films deposited by rf sputtering, e-beam and sol-gel methods [134], 

The absorbance (or optical density) of the films were estimated from the transmittance T using the relation A = -log(T). Here we assumed that all the incident light is either transmitted or absorbed, reflection or scattering being negligible. The Napierian absorption coefficient of the sample was calculated using Lamberts 

The porosity of the nanotube array architecture was determined from the relation [136]  

The absorption coefficient a and the band gap Eg are related through the equation [137] 

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When an analyte lacks measurable optical properties by itself, spectroscopically active intermediate molecules are needed. Indicators modify their optical properties when they interact with the analyte and usually are neutral or ionizable dyes. 

Each requires a very careful calibration of the system in order to obtain the composition from the measured optical property. If only one component is analyzed, then it is essential to show that its optical property is uniquely related to its concentration and is not dependent upon the other substances present. With the exception of optical rotation and refractive index, most of the optical methods do not give better than a 1 per cent accuracy under normal operating conditions, and generally the accuracy is much less. ... 

Fairly wide use has been made of preparative gel electrophoresis in protein chemistry, and in principle there is no reason why the same procedures should not be adopted for use with nucleic acids which have the advantage that much may be accomplished with very small quantities of purified material. Thus, it is relatively easy in many situations to introduce radioactive label at very high levels and specific activity, and the use of for this purpose offers a degree of sensitivity that cannot be matched in work on proteins. The extinction coefficients of nucleic acids are also very high in the ultraviolet, so that with say 20 pg in 1 ml or less it is possible to measure optical properties, thermal melting profiles, sedimentation coefficients, and even molecular weights by sedimentation equilibrium in an instrument equipped with scanner optics. Consequently, the sacrifice of resolution that, by a malign law of nature, always accompanies any attempt to scale up an analytical fractionation method is often at least partly avoided. 

Fig. 21. Molecular structure and measured optical properties of EHO-OPPE. From [22]...

The refractive index remains the most measured optical property of glasses, as well as the most basic optical property for determination of the appropriate glass for many applications. The refractive index of any material is defined as the ratio of the velocity of light in a vacuum divided by the velocity of light in a medium. This ratio can be measured by application of Snell s law, which states that the refractive index, n, is given by the expression ... 

The principles and standard procedures used in the determination of color can be found in ASTM E308. Equipment is conunercially available for measuring optical properties of polymers for these purposes. Major suppliers include Gardner (gloss meter for specular gloss, haze meter for haze and luminous transmittance, and clarity meter for specular transmission) and Hunter Lab (spectrocolorimeter). 

F ure 17-10. Sketch of the setup used to measure optical properties of a sol-gel waveguide doped with erbium/ytterbium ions. Different pigtailed laser diodes and dfferent output coupling configurations may be mixed, in order to perform specific measurements. 

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