Change in refractive index

Here, the wavelength of the laser light is A, and is a correction term due to the wavelength dependence of the refractive index of the etalon material ( = 0.034 at 514.5 nm when fused silica etalons are used to achieve the necessary delay, or = 0 when a lens combination is used). The optical correction term Av/v results from the change in refractive index of the window material with shock stress (Barker and Hollenbach, 1970). If the measure-... 

The dead point is obtained by including in the sample a trace of an unretained solute or, more often, one of the components of the mobile phase. For example, when using a methanol water mixture as the mobile phase, the dead point is obtained from the elution of a pure sample of methanol. The pure methanol can often be monitored, even by a UV detector, as the transient change in refractive index resulting from the methanol is sufficient to cause a disturbance that is detectable. 

Ferroelectric materials are capable of being polarized in the presence of an electric field. They may exhibit considerable anomalies in one or more of their physical properties, including piezoelectric and pyroelectric coefficients, dielectric constant, and optoelectronic constant. In the latter case, the transmission of light through the material is affected by the electric field, which produces changes in refractive index and optical absorption coefficient. Varying the applied field changes the phase modulation. 

Mixed solvents are generally unsatisfactory for use in the determination of polymer molecular weights owing to the likelihood of selective absorption of one of the solvent components by the polymer coil. The excess of polarizabilit f of the polymer particle (polymer plus occluded solvent) is not then equal to the difference between the polarizabilities of the polymer and the solvent mixture. For this reason the refractive increment dn/dc which would be required for calculation of K, or of i7, cannot be assumed to equal the observed change in refractive index of the medium as a whole when polymer is added to it, unless the refractive indexes of the solvent components happen to be the same. The size Vmay, however, be measured in a mixed solvent, since only the dissymmetry ratio is required for this purpose. 

We now focus our attention on the presence of the unperturbed donor quantum yield, Qd, in the definition of R60 [Eq. (12.1)]. We have pointed out previously [1, 2] that xd appears both in the numerator and denominator of kt and, therefore, cancels out. In fact, xo is absent from the more fundamental expression representing the essence of the Forster relationship, namely the ratio of the rate of energy transfer, kt, to the radiative rate constant, kf [Eq. (12.3)]. Thus, this quantity can be expressed in the form of a simplified Forster constant we denote as rc. We propose that ro is better suited to FRET measurements based on acceptor ( donor) properties in that it avoids the arbitrary introduction into the definition of Ra of a quantity (i />) that can vary from one position to another in an unknown and indeterminate manner (for example due to changes in refractive index, [3]), and thereby bypasses the requirement for an estimation of E [Eq. (12.1)]. 

Figure 12. Measurement arm of the Mach-Zehnder interferometer covered by a sensitive polymer layer, resulting in a intensity modulation by a change of the refractive index. This schematic changes are combined with the experimental data on the right side on top the curve of uptake of analyte, and its diffuseion out of the layer (right part), in the middle the experimental modulation, and at the bottom the related changes in refractive index. Bottom left shows the result of intensity signal versus the amount of substance for eight different analytes.

Fig. 13.10a. An MNF was coated with an ultra thin palladium film. The operational principle of this sensor was based on the fact that a thin palladium film has the ability to selectively absorb hydrogen. If a palladium film is exposed to hydrogen, its refractive index, and, in particular, absorbance, changes. The change in refractive index causes a change in transmission power of an MNF. The MNF fabricated in Ref. 15 had a palladium film of 4 nm in thickness and 2 mm in length. In Fig. 13.10b, the transmission power of the MNF is shown as a function of time when the sensor was exposed successively to a 3.9% concentration of hydrogen. The response time calculated from the plot was 10 s. This response time is 3 5 times faster than that of other optical hydrogen sensors and about 15 times faster than that of some electrical nano hydrogen sensors. The fast response of the sensor is, presumably, due to the ultra small thickness of the palladium film that is rapidly filled with hydrogen. Figure 13.10c shows the transmission of this sensor as a function of time for...

The change in refractive index of the reaction mixture can be used to follow the progress of reaction provided all the constituents present in the... 

Light is reflected from the surface of the fiber, due to the change in refractive index from air into polymer (for PET, n = 1.6). This is specular reflection, similar to reflection from a mirror, and causes no coloration of the reflected light. 

Polymer transparency also requires that the crystalline regions be smaller than the wavelength of light, since these regions also represent changes in refractive index. Larger crystallites will scatter light at their interfaces and make the PET opaque. 

This expression is independent of the film thickness. Thus, when one considers reflective monitoring of metal film etching, only at the interface between film and substrate will a change in reflectivity be observed due to the change in refractive index. Although this is extremely useful for end point detection one still must apply films of known thickness for cases in which etch rate information is desired. 

The product darkens a little on standing but undergoes no change in refractive index. 

As the light reaches each slab, some is reflected due to the change in refractive index. For the right spacing of the slabs, the reflected rays from each slab are in phase with each other but out of phase with the incident light. For such wavelengths, the incident and reflected rays cancel each other. 

Birefringence induced by applied stress is caused by the two components of the refracted light traveling at different velocities. This generates interference which is characteristic of the material. The change in refractive index, An, produced by a stress S is often related by a factor C called the stress-optical coefficient as follows ... 

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