Optical properties refractive coefficients

LB films are ideally suited to analysis by the SPR technique. They may easily be deposited onto a silver-coated microscope slide, and produce a uniform reproducible dielectric layer with a thickness of roughly 2-3 nm per layer, dejpending on molecular size and orientation. For such films, the linear optical properties (refractive index and absorption coefficient) and the thickness may be obtained straightforwar y as described. 

Optical Properties. The index of refraction and extinction coefficient of vacuum-deposited aluminum films have been reported (8,9) as have the total reflectance at various wavelengths and emissivity at various temperatures (10). Emissivity increases significantly as the thickness of the oxide film on aluminum increases and can be 70—80% for oxide films of 100 nm. 

It should be noted that low-loss spectra are basically connected to optical properties of materials. This is because for small scattering angles the energy-differential cross-section dfj/dF, in other words the intensity of the EEL spectrum measured, is directly proportional to Im -l/ (E,q) [2.171]. Here e = ei + iez is the complex dielectric function, E the energy loss, and q the momentum vector. Owing to the comparison to optics (jqj = 0) the above quoted proportionality is fulfilled if the spectrum has been recorded with a reasonably small collection aperture. When Im -l/ is gathered its real part can be determined, by the Kramers-Kronig transformation, and subsequently such optical quantities as refraction index, absorption coefficient, and reflectivity. 

Optical Properties.—The refractive index of tantalum is 2-05, the coefficient of absorption 2-31, and the reflexion capacity 43-8 per cent, when measured with yellow light of wave-length A=5790.5 The spectral emissivity and the radiation intensity and their variation with temperature have been measured by Worthing.6 For a comparison of the radiation constants of tantalum, platinum, osmium and carbon, see the references cited.7 The flame spectrum of tantalum between carbon electrodes consists of a blue cone with a reddish-yellow edge.8... 

The optical properties, such as the refractive index and the absorption coefficient, are independent of light intensity... 

In the discussion of the piezoelectric effect in Chapter 6 the tensor character of the permittivity of a dielectric was recognized although attention was focused on the piezoelectric coefficients. Because the optical and electro-optical properties of dielectrics are determined by their refractive indices or, equivalently, by their permittivities (see Eq. (2.120)), it is now necessary to consider these parameters in some detail. 

A completely different behaviour exhibit NBF from NaDoS solutions. They do not change their thickness with pa and Cei alterations. However, their properties depend on the composition of the initial surfactant solution (see 0(Cei) and ta(Cei) dependences in Section 3.4.1.1). The thickness of NBF determined from h(Cei) dependence is approximately equal to the doubled thickness of the adsorption layer as assumed by Perrin [318]. This is confirmed by NBF obtained from other surfactants. It should be bom in mind that the interferometric technique employed to measure film thickness gives directly the optical difference in the path of the beams reflected by the two film surfaces. When the thickness is calculated from optical measurements a refractive coefficient, being a function of film structure, should be chosen (see Sections 2.1.3 and 3.4.1). 

As the local electric field in the particles is enhanced at the SPR, the metal nonlinear optical response can be amplified as compared to the bulk solid one. Moreover, the intrinsic nonlinear properties of metals may themselves be modified by effects linked with electronic confinement. These interesting features have led an increasing number of people to devote their research to the study of nonlinear optical properties of nanocomposite media for about two decades. Tire third-order nonlinear response known as optical Kerr effect have been particularly investigated, both theoretically and experimentally. It results in the linear variation of both the refraction index and the absorption coefficient as a function of light intensity. These effects are usually measured by techniques employing pulsed lasers. 

The sign and magnitude of the resulting thermal nonlinear refraction coefficient (which is, actually, a pure linear effect [219]) depend on the thermo-optical coefficient 9 /9r of the material. This coefficient has sometimes been assimilated to the one of the surrounding host only [132, 218], but we have recently shown that, due to local field enhancement at the SPR, they can be very different - even for weakly concentrated media exactly as for the pure electronic nonlinear properties as demonstrated in Section 3.2.4. Moreover, an absorptive thermo-optical effect, which is always disregarded in the literature, can occur parallel to the refractive one. These conclusions will be published soon. 

Electro-optic effects refer to the changes in the refractive index of a material induced by the application of an external electric field, which modulates their optical properties [61, 62], Application of an applied external field induces in an optically isotropic material, like liquids, isotropic thin films, an optical birefringence. The size of this effect is represented by a coefficient B, called Kerr constant. The electric field induced refractive index difference is given by... 

As everyone knows, the optical properties of a material are expressed in two optical constants, the refractive index n and the absorption coefficient x. It is the purpose of spectroscopy to determine experimentally one or both of these optical constants as a function of frequency. This can be done by measuring reflection or transmission. If we were able to measure amplitudes or electrical fields (magnitude and phase) in an optical investigation, it would generally be possible to deduce both optical constants from one measurement of either reflection or transmission. However, we are only able to measure intensities where the magnitude of the field is determined and the phase information is lost. Thus, in general, from one item of information only one optical constant is obtained, and two measurements are necessary to determine both. There are a few exceptions to this rule, e.g. the... 

Since petroleum is a mixture, its physical properties vary considerably, depending upon the type and proportions of the hydrocarbons and impurities present. These physical properties include the density, viscosity, optical activity, refractive index, color, fluorescence, odor, pour- and cold-points, flash- and burning-points, coefficient of expansion, surface and interfacial tension, capillarity and absorption. 

Polymers have many important optical properties, such as the refractive index, reflection, scattering, absorption, clarity, gloss, haze, birefringence, stress-optic coefficient, the yellowing induced by photochemical degradation, and the specific refractive index increment in dilute solutions. Its optical properties need to be considered in evaluating the potential usefulness of a polymer in many applications such as (but not limited to) compact disk coatings, automotive... 

The anisotropy of the optical properties in the wavelength range of visible light is generally described by the birefringence An, defined by the first part of Equation 8.12. A birefringent material has different refractive indices in two different principal axis directions. For a specimen that is under uniaxial tension, nn and n denote the refractive indices parallel and perpendicular to the orientation direction, respectively. The second part of Equation 8.12 defines the stress-optic coefficient C0 describing the dependence of An on the applied stress. 

The superposition of two intersecting optical pulses can generate grating-like modulations in the optical properties of the excited material. For example, the modulation amplitudes for n, the real part of the index of refraction, and K, the (spatial) absorption coefficient as functions of the probe wavelength are... 

Figure 14 illustrates the viability of the PFS method, but here it is worth taking stock of the assumptions that underpin PCS and PFS. A principal virtue of size estimates derived from PCS are that they are independent of the optical properties of the particle. They are however implicitly dependent on the particle shape, for the shape is required to determine the translational diffusion coefficient in the suspending medium. The particles are usually assumed to be spherical. The aspect ratios displayed in Figure 13 were reconstracted assuming the size of the particles and their refractive index was known, and... 

---