Evanescent wave polarization

The isotropic part has not changed. The quasi pressure (qP) curve splits up into a real and an imaginary branch . During this real part the transversal share of the polarization increases until the wave becomes a quasi shear vertical wave. Furthermore, the wave is not anymore a propagating but an evanescent wave in this part. The branch is again only real, it is part of the quasi shear vertical (qSV) curve of the homogeneous case (dotted line), its polarization is dominated by the transversal share and the wave is a propagating one. For the branches (real) and... 

Fig. 10. A SPR Detection realized in a BIAcore system. A fan of polarized light passes a prism and is focused at the interface to an aqueous phase under conditions of total reflection. An evanescent wave enters the solvent phase. If the prism is coated with a thin gold layer at the interface the free electrons in the metal absorb energy from the evanescent wave for a distinct angle, depending on the refractive index of the solvent near the interface. B The gold layer can be modified with, e.g., a carboxydextrane matrix, where catcher molecules can be immobilized by standard chemistry. If a ligand is applied with the aqueous phase it may interact with the catcher and accumulate in the matrix, causing a shift in the resonance angle. If no specific binding occurs the refractive index in proximity of the sensor is less affected...

In SPR experiments -polarized light of a certain wavelength strikes the interface between the two media,71 72 which is coated with a thin metal film. The wave vector of the evanescent wave is given by the following equation 71... 

The factor 1(0) in Eq. (7.2) is a function of 8 and the polarization of the incident light these features are discussed shortly. However, we first examine the remarkable amplitude, polarization, and phase behaviors of the electric fields [from which 1(0) is derived] and the magnetic fields of the TIR evanescent wave. The field components are listed below, with incident electric field amplitudes Aps and phase factors relative to those of the incident E field s phase at z = 0. (The coordinate system is chosen such that the x-z plane is the plane of incidence. Incident polarizations p and s are parallel and perpendicular to the plane of incidence, respectively.)... 

The collected fluorescence 3F [from Eq. (7.39)] clearly depends on the orientation distribution of the dipoles and the incident polarization through the dependences on 0 and E. We will assume a special but common case here randomly oriented dipoles with a z-dependent concentration near the surface, excited by a p-polarized evanescent wave. 

The polarization properties of the evanescent wave(93) can be used to excite selected orientations of fluorophores, for example, fluorescent-labeled phosphatidylethanolamine embedded in lecithin monolayers on hydrophobic glass. When interpreted according to an approximate theory, the total fluorescence gathered by a high-aperture objective for different evanescent polarizations gives a measure of the probe s orientational order. The polarization properties of the emission field itself, expressed in a properly normalized theory,(94) can also be used to determine features of the orientational distribution of fluorophores near a surface. 

Figure 2. Qualitative behavior of the field strength of the evanescent wave as a function of the angle of incidence (nt — 1,51 n -= 1.0). Contrary to the behavior of the electromagnetic field of normal" light the evanescent field comprises a longitudinal component, too. E and E respectively indicate the direction of polarization of the incident light.

The third term is a damping term, which allows for the possibility that a wave is absorbed by the medium this is called the evanescent wave and the quantity a is also called the optical conductivity (at zero frequency it becomes the electrical conductivity). The evanescent wave is exploited in near-field scanning optical microscopy. If waves propagate along x, so that <)/ <)y = 0, d/dz = Q, then EX = HX = 0. Next, assume Ey(x,t)=f(x)exp(icot) = 0 and Ez(x,t)=g(x)exp(icot) = 0 that is, assume plane-polarized light with the E vector in the xy plane Then the differential equation to be solved is more simply... 

Another feature that has not been systematically covered concerns additional means of determining properties of adsorbates. Examples here are the classical spectroscopies, with their surface variants (secs. 1.7.10-12), reflection methods, including elllpsometry, reflectometry and evanescent wave studies, NMR. X-ray analysis, neutron diffraction and dielectric spectroscopy. The theory of the last mentioned phenomenon for bulk phases has been discussed in sec. I.4.5f if applied to adsorbates, the technique can give information on the various degrees of freedom that polar molecules may have, say, for water adsorbed on oxides. For thicker water layers containing ions, measurement of the surface conductivity may yield additional information see also sec. I.6.6d. The reason for not systematizing these techniques is that we do not consider them typically "surface methods, but rather surface variants of bulk methods. 

Solutions for the scattering of evanescent waves by a sphere were studied initially by Chew et al. in 1979 (68). Evanescent wave is generated from a dielectric/air plane interface due to total internal reflection and is scattered by a dielectric sphere. Quinten et al, on the other hand, derived the total cross section for extinction and scattering of evanescent waves by a small metal particle (69). In these studies, a particle with smaller size is placed away from the plane interface, and therefore the multiple scattering between the sphere and the plane interface is ignored. Quinten s study further supports that the extinction cross section for the extinction of p-polarized evanescent waves by a metallic nanoparticle is larger than that for s-polarized evanescent waves and plane waves. This can be attributed to the... 

GNP is 0.166 + 3.15/ at X= 650 nm (72). The evanescent waves with s- orp-polarization from the interface of the fiber core are coupled wdth the localized surface plasmon of the GNP. 

In ATR-FTIR excitation occurs only in the immediate vicinity of the surface ol the reflection element, in an evanescent wave resulting from total internal reflection. The intensity of the evanescent field decays exponentially in the direction normal to the interface with a penetration depth given by (1.7.10.121, which for IR radiation is of the order of a few hundreds of nm. Absorption leads to an attenuation of the totally reflected beam. The ATR spectrum is similar to the IR transmission spectrum. Only for films with a thickness comparable to, or larger than, the penetration depth of the evanescent field, do the band intensities depend on the film thickness. Information on the orientation of defined structural units can be obtained by measuring the dichroic ratio defined as R = A IA, where A and A are the band absorbances for radiation polarized parallel and perpendicular with respect to the plane of incidence, respectively. From this ratio the second-order parameter of the orientation distribution (eq. [3.7.13]) can be derived ). ATR-FTIR has been extensively used to study the conformation and ordering in LB monolayers, bilayers and multilayers of fatty acids and lipids. Examples of various studies can be found... 

Both the optical and the electrical trapping have already been demonstrated separately. The double evanescent wave trap for atoms has been proposed in Ref. [Ovchinnikov 1991] and has been demonstrated in Ref. [Hammes 2002] for Cs atoms. Bezryadin and coworkers [Bezryadin 1997] have reported a method of fabrication for nanoscale controllable break junctions, in which the polarized nano-clusters, such as Pd clusters, have been trapped between the electrodes. The nano-clusters were self-assembled in the region of the maximum field in order to produce a wire connecting the tips [Bezryadin 1997],... 

Under the total internal reflection (TIR) condition, light penetrates into materials with lower refractive index from a glass plate with higher value. This is called an evanescent wave and can be used as excitation and probe beams for surface photochemical studies. In the case of s-polarization, an intensity of this wave is given by the following equations. 

---