Optical constants orientation

Turner (1973) and McKellar (1976) applied RG theory to ensembles of randomly oriented particles of arbitrary shape the former author included spheres with anisotropic optical constants. Optically active particles have been treated within the framework of the RG approximation by Bohren (1977). 

We have discussed intrinsically anisotropic particles—ones with anisotropy originating in their optical constants rather than their shape—in previous chapters. In Section 5.6 we gave the solution to the problem of scattering by an anisotropic sphere in the Rayleigh approximation. From the results of that section and Section 5.5 it follows that the average cross section (C) (scattering or absorption) of a collection of randomly oriented, sufficiently small, anisotropic spheres is... 

Common liquids are optically isotropic, and the solids that physicists seem to like most are cubic and therefore isotropic. As a consequence, treatments of optical properties, particularly from a microscopic point of view, usually favor isotropic matter. Among the host of naturally occurring sohds, however, most are not isotropic. This somewhat complicates both theory and experiment for example, measurements of optical constants must be made with oriented crystals and polarized light. But because of the prevalence of optically anisotropic solids, we are compelled to extend the classical models to embrace this added complexity. 

More problems must be faced when trying to extract optical constants from measurements on particles of anisotropic solids. Random orientation of the particles averages somehow the two or three sets of optical constants. We... 

From the data reported in Fig. 2.2 and from spectroscopic ellipsometry measurements, the anisotropic complex optical constants of oriented PPV have been determined [32,69]. Several different data analyses, described previously, were carried out on the 7Z and T spectra in order to extract n, both below and above the HOMO-LUMO transition (transparent free-standing film and bulk material, respectively). In order to evaluate n below 1.6 eV, where the sum of 1Z and T is equal to 1 within experimental error, a numerical inversion of the 7Z and T spectra was performed by assuming k = 0... 

Ellipsometry measures the orientation of polarized light undergoing oblique reflection from a sample surface. Linearly polarized light, when reflected from a surface, will become elliptically polarized, because of presence of the thin layer of the boundary surface between two media. Dependence between optical constants of a layer and parameters of elliptically polarized light can be found on basis of the Fresnel formulas described above. 

Another useful method, especially when only a single wavelength is available, is the different dependence of Y and surface electric field on the polarisation and angle of incidence.72 From the Fresnel equations and the known optical constants of metals the electric field experienced by the adsorbate and the absorbance of the substrate can be calculated. 72.73 por substrate excitation Y should follow (1-R). For adsorbate excitation some knowledge (or model) of the symmetry of the adsorbate layer (orientation of transition dipole) is required to relate the electric field to the excitation probability. The angle of incidence dependence of Y for different input polarisations have been calculated for some typical cases.72.74 Cavanagh s group have... 

Besides, both s tructures posses an optical anisotropy in the spectral range of X a where a i s the "lattice" constant. This is the so called anisotropy of shape described in [4]. Studies of birefringence in 2D PC from macroporous silicon [5] shows it is a positive uniaxial crystal with its optical axis oriented along the pores. The present work is focused on the studies of ID PC from grooved Si. It is expected to be a negative uniaxial crystal whose axis is perpendicular to the Si ribs. 

ZnSe/D20/monolayer of pyridine/ZnSe) from the optical constants, using the matrix method and assuming that pyridine molecules are oriented with the C2 axis perpendicular to the metal surface. Taken with permission from Refs. [36] and [40]. 

The correction of the measured PM IRRAS signal for the PEM response functions was introduced in the studies of the potential-induced reorientation of a film formed by 4-pentadecyl pyridine [81], one year later. For the first time, the absorbance of a Langmuir film adsorbed at the electrode surface was determined in that paper. The theoretical spectrum of a film of randomly oriented molecules was calculated from independently measured optical constants, and tilt angles of the pentadecyl chain and the pyridine moiety were determined using the absolute method and Eq. (44). This work laid the methodological foundations for future PM IRRAS studies on monolayers and bilayers formed by amphiphilic molecules at electrode surfaces. 

DETERMINATION OF MOLECULAR PACKING AND ORIENTATION IN ULTRATHIN FILMS ANISOTROPIC OPTICAL CONSTANTS OF ULTRATHIN FILMS... 

The MO measurements provide information about the angular distribution of molecules in the x, y, and z film coordinates. To extract MO data from IR spectra, the general selection rule equation (1.27) is invoked, which states that the absorption of linearly polarized radiation depends upon the orientation of the TDM of the given mode relative to the local electric field vector. If the TDM vector is distributed anisotropically in the sample, the macroscopic result is selective absorption of linearly polarized radiation propagating in different directions, as described by an anisotropic permittivity tensor e. Thus, it is the anisotropic optical constants of the ultrathin film (or their ratios) that are measured and then correlated with the MO parameters. Unlike for thick samples, this problem is complicated by optical effects in the IR spectra of ultrathin films, so that optical theory (Sections 1.5-1.7) must be considered, in addition to the statistical formulas that establish the connection between the principal values of the permittivity tensor s and the MO parameters. In fact, a thorough study of the MO in ultrathin films requires judicious selection not only of the theoretical model for extracting MO data from the IR spectra (this section) but also of the optimum experimental technique and conditions [angle(s) of incidence] for these measurements (Section 3.11.5). 

To quantify the orientation of a pulmonary surfactant-specific protein SP-C incorporated into simple and mixed-lipid monolayers at the AW interface, Ger-icke et al. [848] applied the spectrum fitting procedure using the optical constants expressed by Eq. (3.56). This protein is a promoter of the spreading... 

In papers [6,7] it is reported that the orientational mechanism of nonlinearity of the LC oriented mesophase can cause very large values of nonlinear optical constants the constants of light amplification in the stimulated scattering in NLC [6] and in smectic LC [7]. The point is, that variations of the NLC director direction lead to very large changes of its optical properties, because = j[ - 0.5—1 (/i and are the... 

---