Absolute refractive index

In theory, (7.3) can be used to calculate either the absolute refractive index (n) or the absolute length (L) of the cavity if one of them is known. However, the measurement based on (7.3) has a poor resolution because the period is not a sensitive function of the optical path change6 7. 

Comparing (7.3) and (7.6), one finds that (7.3) can be used to calculate the absolute refractive index while (7.6) only provides the relative change of the refractive index. However, the calculation based on (7.6) has a much higher resolution than that obtained using (7.3). 

The main objectives in calibrating the SEC detection system in absolute refractive index and absorption units are the estimation of v and E at the normal flow conditions and the standardization of the measurement errors. The first step in the calibration process is the estimation of the instrument s constants to transform the computer units into absorbances and refractive index units. The Waters AAO UV spectrophotometer displays absorbance units. Therefore, step changes in the instrument s balance and sampling of the signal provide the necessary data for the calibration. The equations obtained are ... 

In order to evaluate the properties of photochromic dyes for photonics applications, we have to measure absolute refractive index values, their changes and their wavelength dispersions. Absolute refractive index measurements are needed because design of photonic devices strongly depend on these values as long as they take advantage of changes in refraction, reflection and phase shift. Some papers... 

Symbol n. The absolute refractive Index of a medium is the ratio of the speed of electromagnetic radiation in free space to the speed of the radiation in that medium. As the refractive index varies with wavelength, the wavelength should be specified. It is usually given for yellow Ught (sodium D-lines wavelength 589.3 run). The relative refractive index is the ratio of the speed of light in one medium to that in an adjacent medium. See... 

Sorensen HS, Pranov H, Larsen NB, Bomhop DJ, and Andersen PE (2003) Absolute refractive index determination by microinterferometric backscatter detection. Analytical Chemistry 75 1946-1953. 

The constant is a direct measure of the refractive power of a medium for a given wavelength X and is called the index of refraction or refractive index (RI) or absolute refractive index of the medium and denoted Hence, the RI index of refraction is a dimensionless physical quantity defined as the ratio of the celerity of light in a vacuum, c, to the celerity of the electromagnetic radiation in a medium, 7, in m.s By definition the index of refraction of a vacuum is taken arbitrarily to equal unity ... 

Figure 6. Refractive index change for thin films of ABD-grafted compounds. The refractive index change is plotted in absolute refractive index units with zero meaning no change in the refractive index after irradiation with 350nm light.

The vast majority of refractive index detectors are differential detectors where the refractive index of the sample is measured relative to a reference liquid. This enables them to be used in a wide range of applications but requires a fairly delicate flow cell. Absolute refractive index detectors are available which although only covering a limited range and less sensitive, are more robust and have sensor probes which can be easily inserted in the process stream. These are especially suited to explosion proof applications. 

Let us present some fundamental laws of optics later we shall use them from the point of view of the wave nature of light. Consider a beam of light falhng on the border of two media 1 and 2 with absolute refraction indexes and 2 (Figure 6.3). The medium with the higher refraction index is referred to as the optically denser one (Figure 6.3, < Wj)... 

In the case of Langmuir monolayers, film thickness and index of refraction have not been given much attention. While several groups have measured A versus a, [143-145], calculations by Knoll and co-workers [146] call into question the ability of ellipsometry to unambiguously determine thickness and refractive index of a Langmuir monolayer. A small error in the chosen index of refraction produces a large error in thickness. A new microscopic imaging technique described in section IV-3E uses ellipsometric contrast but does not require absolute determination of thickness and refractive index. Ellipsometry is routinely used to successfully characterize thin films on solid supports as described in Sections X-7, XI-2, and XV-7. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

Infrared ellipsometry is typically performed in the mid-infrared range of 400 to 5000 cm , but also in the near- and far-infrared. The resonances of molecular vibrations or phonons in the solid state generate typical features in the tanT and A spectra in the form of relative minima or maxima and dispersion-like structures. For the isotropic bulk calculation of optical constants - refractive index n and extinction coefficient k - is straightforward. For all other applications (thin films and anisotropic materials) iteration procedures are used. In ellipsometry only angles are measured. The results are also absolute values, obtained without the use of a standard. 

Synthetic, nonionic polymers generally elute with little or no adsorption on TSK-PW columns. Characterization of these polymers has been demonstrated successfully using four types of on-line detectors. These include differential refractive index (DRI), differential viscometry (DV), FALLS, and MALLS detection (4-8). Absolute molecular weight, root mean square (RMS) radius of gyration, conformational coefficients, and intrinsic viscosity distributions have... 

To correct a refractive index determined for airjliquid to the absolute index vacutimlliquid, the observed value should be multiplied by I 00029. This correction is, however, too small to be of the slightest value in practice. 

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

Equation (7.1) states that the intensity of the interference signal is a periodic function of the cavity length, the refractive index, and the wavelength. For most chemical sensing applications, the interference signal needs to be processed to obtain either the absolute value or the relative change of the refractive index that... 

Several kinds of detection systems have been applied to CE [1,2,43]. Based on their specificity, they can be divided into bulk property and specific property detectors [43]. Bulk-property detectors measure the difference in a physical property of a solute relative to the background. Examples of such detectors are conductivity, refractive index, indirect methods, etc. The specific-property detectors measure a physico-chemical property, which is inherent to the solutes, e.g. UV absorption, fluorescence emission, mass spectrum, electrochemical, etc. These detectors usually minimize background signals, have wider linear ranges and are more sensitive. In Table 17.3, a general overview is given of the detection methods that are employed in CE with their detection limits (absolute and relative). 

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