INDEX interferometric method

The four general methods of measuring refractive index are the Christiansen, the Frensel. the beam deflection, and the interferometric methods. Today, the most commonly applied technique in HPLC is the beam deflection method. 

One of the methods to determine D is to measure da/dt, also called the flux, and then find dc/dx from it. From this value we can obtain D as the flux obeys Flck s first law. Due to diffusion the composition and therefore the refractive index of the solution changes. Most of the methods for measuring rate of diffusion involve measurement of such changes in the refractive indices with the help of such techniques as light absorption, fluorescence and Tindall effect. More recently the interferometric methods of studying the boundary changes have been preferred. 

Sabat, R. G., Rochon, P. (2009a). The dependence of the refractive index change of clamped relaxor ferroelectric lead lanthanum zirconate titanate (PLZT) ceramics on AC and DC electric fields measured using an interferometric method. Ferroelectrics, Vol. 386, No. 1, pp. 105. 

Methods for the analysis of phosgene in the presence of HCl have involved interferometric techniques [1235,1967]. In one example, the refractive index of the gas mixture was measured by use of an interferometer, in order to calculate the composition of the mixture [1967]. In another example, a rapid method for the continuous analysis of phosgene (in the off-gases from the production of alkyl isocyanates) involved an interferometric technique in which the number of interference iines were correlated as a function of phosgene concentration [1235]. 

The particle concentration of the eluent is normally measured by means of infrared or ultraviolet photometers. Additionally, fluorescence photometer, interferometric measurements (for the refractive index), or mass-spectroscopic methods (e.g. induced coupled plasma mass spectroscopy—ICP-MS, Plathe et al. 2010) are employed. The combination of different detection systems offers an opportunity for a detailed characterisation of multi-component particle systems. Note that the classification by FFF is not ideal and the relevant material properties are not always known moreover, the calibration of FFF is rather difficult. The attribution of particle size to residence time, thus, bears some degree of uncertainty. Recent developments of FFF instrumentation, therefore, include a particle-sizing technique additional to the flow channel and the quantity measurement (usually static and dynamic light scattering, Wyatt 1998 Cho and Hackley 2010). 

A number of methods have been used to measure the EO coefficients and ni of the poled polymer samples. These EO measurements are made by detecting the change in refractive index of the poled polymer sample when a modulating electric field is applied to the sample. Mach-Zehnder [42,43]. Fabry-Perot [44,45], and Mich-elson [46] interferometric techniques have been used to evaluate the EO coefficients. Other techniques, such as an attenuated total reflection technique [47,48] and an ellipsometric technique [49-51], have also been employed to determine the r coefficients. 

Much of the fundaments we know about surface forces are based on experiments with the SFA. With the SFA, surface forces are measured between two atomically smooth mica surfaces. Distance is measured interferometrically, which allows absolute determination of separation distance with a resolution of typically 0.1 nm (with down to 25 pm achievable). Its absolute force sensitivity is not as high as in several other methods, but in terms of the usually more relevant force per unit area, its sensitivity is excellent. Lateral (friction) forces can be measured in addition to normal standard force versus distance measurements and have contributed much to our understanding of lubrication by thin films. Additional information such as refractive index and contact area can be obtained. The main reason for the limited number of groups using this instrument is the difficult operation of such a system that needs a very experienced and skillful expert. The large interaction areas demand a contamination-free surface preparation and can lead to significant hydrodynamic forces in highly viscous media, which could make equilibrium measurements hard to achieve. 

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