Polarization upon reflection

In the general case, when s-polarized light is converted into p-polarized light and/or vice versa, the standard SE approach is not adequate, because the off-diagonal elements of the reflection matrix r in the Jones matrix formalism are nonzero [114]. Generalized SE must be applied, for instance, to wurtzite-structure ZnO thin films, for which the c-axis is not parallel to the sample normal, i.e., (1120) ZnO thin films on (1102) sapphire [43,71]. Choosing a Cartesian coordinate system relative to the incident (Aj) and reflected plane waves ( > ), as shown in Fig. 3.4, the change of polarization upon reflection can be described by [117,120]... 

Iv) Ellipsometry. With ellipsometry one measures not only reflected intensities, but also the changes in polarization upon reflection. The technique has been discussed in sec. 1.7.10b. 

Ellipsometry is a reflectance technique that depends on the optical constants and thickness of surface layer. For colorless layers, a polarized light beam will change its plane of polarization upon reflection by the surface film. The thickness can sometimes be determined when optical constants are known or approximated by constants of the bulk material. Antibody-antigen surface reaction can be detected this way. 

Changes in the state of polarization upon reflection at an interface are given by... 

Ellipsometry is a reflectance method in which the change of the state of polarization upon reflection is determined. This change is described in terms of two ellipsometric angles A and 9 given by ... 

Generally, upon reflection from the metal surface, the beam changes its phase depending upon the angle of incidence 0 and the polarization of the beam. Figure 2... 

Unlike grazing angle reflection studies of films on metals, both parallel and perpendicularly polarized radiation is observable upon reflection from the water surface. Similar to ATR experiments, electric fields in all three dimensions relative to the water surface are present, indicating the potential for complete orientation studies of the surface layers 126). 

The main experimental technique applied in this chapter is SE. Several textbooks were written on SE [73,114-118], Therefore, only some basic concepts are described. SE examines the relative phase change of a polarized light beam upon reflection (or transmission) at a sample surface. In Fig. 3.4 the setup of an ellipsometry experiment is shown. Upon model analysis of the experimental data, the DFs and thicknesses of the sample constituents can be extracted. Two different experimental approaches have to be distinguished, standard and generalized ellipsometry. 

An example of the influence of mobile-phase polarity upon the retention and selectivity of sample molecules is shown in Figure 5-51. In normal phase, the most polar compound is retained the longest. This is reflected by the observation that the dimethyl phthalate is the most polar and is retained the longest. By changing from ethyl acetate to butyl acetate, the overall mobile phase is less polar and, hence, all of the compounds increase in retention. However, in addition, there is one change in selectivity between the diethyl and the diphenyl molecules. 

The phase shift upon reflection at the interfaces depends on both the angle of reflection ip and on the polarization of the electromagnetic wave (TE or TM). 

On metal surfaces, two additional selection mles apply. The first is that only vibrations perpendicular to the surface are HREELS active. This mle follows from two phenomena unique at metal surfaces " (i) Electromagnetic waves polarized perpendicularly to the plane of incidence (parallel to the plane of the surface) undergo a 180° phase shift upon reflection. That is, at the metal surface, the out-of-phase electric-field vectors of the incident and reflected waves cancel each other as a result, no field exists that can couple with dipoles that oscillate parallel to the surface, (ii) The dynamic dipole moment generated by an oscillator that vibrates in the surface-parallel direction is cancelled by that of its image dipole (Figure 1) hence, there the net dynamic dipole moment is zero. On the other hand, if the real dipole is oriented perpendicularly to the surface, its dynamic dipole moment is reinforced by that of its image dipole. This selection mle is the same as that for infrared reflection-absorption spectroscopy (1RAS).°... 

A technique that can possibly measure the thickness of an anodic film is ellipsometry [21-23]. Figure 10.15 illustrates the setup of an ellipsometer and how is works. A light beam of known polarization reflects and passes through a sample. The polarization change between the incident and reflective beams, expressed as tan —the amplitude (of electrical filed, E) change upon reflection and A—the phase shift, is measured. Since... 

Fig. 4. Phase shifts upon reflection on a metal surface for p- and s-polarized radiation, (a) Incident and reflected field vector (b) phase shift as a function of the angle of incidence.

Contrary to external reflection, where the field amplitude for s-polarized radiation is zero upon reflection, in the case of internal reflection the amplitude of the field at the reflecting surface is not zero for any direction of the field. The magnitude of the amplitude depends on the angle of incidence and on the difference of the refractive indices [33]. 

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