Reflection phase change

The preparation of the reflecting silver layers for MBI deserves special attention, since it affects the optical properties of the mirrors. Another important issue is the optical phase change [ ] at the mica/silver interface, which is responsible for a wavelength-dependent shift of all FECOs. The phase change is a fimction of silver layer thickness, T, especially for T < 40 mn [54]. The roughness of the silver layers can also have an effect on the resolution of the distance measurement [59, 60]. 

The sharpness of the transition in pure lipid preparations shows that the phase change is a cooperative behavior. This is to say that the behavior of one or a few molecules affects the behavior of many other molecules in the vicinity. The sharpness of the transition then reflects the number of molecules that are acting in concert. Sharp transitions involve large numbers of molecules all melting together. 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

When using the thin silica spacer layer, however, it was found that the results from the above-mentioned methods did not agree with the direct measurements from the Taly-surf profilemeter, as shown in Fig. 4(a). This was tentatively ascribed to the effect of penetration of the reflecting beam into the substrate. With a very thin silica layer, the depth of penetration and thus the phase change would depend upon the thickness of the silica spacer layer and also upon that of any oil film present. 

The most important situation occurs when a film of different optical properties is formed at the electrode surface. In this case, theory predicts that the R value can be changed, even for non-absorbing films, as a result of existence of a third phase with different refractive index interspaced between the electrode and electrolyte. Therefore, the entire observed decrease in reflectivity R is not necessarily caused by the absorption of radiation in the film. This approximation, is, however, reasonably acceptable when the film is supported by a highly reflective phase, such as smooth metal electrode. 

While s-polarized radiation approaches a phase change near 180° on reflection, the change in phase of the p-polarized light depends strongly on the angle of incidence [20]. Therefore, near the metal surface (in the order of the wavelength of IR) the s-polarized radiation is greatly diminished in intensity and the p-polarized is not [9]. This surface selection rule of metal surfaces results in an IR activity of adsorbed species only if Sfi/Sq 0 (/i = dipole moment, q = normal coordinate) for the vibrational mode perpendicular to the surface. 

P-polarised light can be reduced to two components Px polarised parallel to the surface and Ps polarised perpendicular to the surface. The Px component also suffers a 180° phase change on reflection for all 9 and is thus blind to any surface species. However, the phase shift for the Pz component changes rapidly with 9. This results in the ratio of the standing wave/incident ray mean electric held strength, <( >/<( ,2 >, varying with 9 as shown in Figure 2.42. The above discussion has two important implications ... 

Not only the phase change but also the amplitudes of the parallel and perpendicular electric field components change upon reflection, and do so differently when an adsorbate is present. The associated variation, indicated as 3 ( can in principle be used as well, but is an order of magnitude smaller than dA. 

PHASE CHANGE OF REFLECTED LIGHT DEPENDS UPON... 

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