Optical effect

In all the studies mentioned, the optical effect caused by the accumulated products of any electrode reactions (formally, by the appearance of an ultrathin film at the interface) was ignored. This effect produces the baseline distortions in the regions of the absorption bands of the solvent (Fig. 3.27). Using the air-water interface as an example, Buffeteau et al. [247] demonstrated that to reproduce these distortions correctly, the optical constants of interfacial rather than bulk water should be used in the spectrum simulations. As underlined by Chazalviel et al. [146, 147] for ATR spectra of a film at the semiconductor-water interface, the uncompensated absorption of the solvent due to increasing the film thickness can be either negative or positive. If the film is compact and has a low refractive index (this is 

INTERPRETATION OF DYNAMIC IR SPECTRA TWO-DIMENSIONAL CORRELATION ANALYSIS 

Spectra measured using phase-sensitive detection when a periodic perturbation is applied frequency domain) as well as spectra measured as a function of time (a time domain) or any other state parameter of the system (e.g., a temperature, pressure, strain, distance, concentration domain) are referred to, by convention, as dynamic spectra to distinguish them from ordinary static (average) spectra. Dynamic spectra can offer an advanced opportunity for separating contributions of different subsystems to spectra of complex systems and quantifying the characteristic half-lives of these subsystems. This opportunity is especially valuable when complex spectra such as the spectra of electrode-electrolyte interfaces and biological films are interpreted. Below we will consider interpretation of dynamic IR spectra, while the technical side of the problem is discussed in Section 4.9. 

Frequency-D(main Spectra. The principle behind extraction of dynamic information from absorption modulation spectra is based on the fact that when a 

However, application of the above technique can be problematic when strong solution-phase absorption obscures weak bands of a surface species. To overcome this limitation, the phase rotation approach [263] can be used. Phase-sensitive detection such as with a lock-in amplifier (LIA) provides two signals the signal that is in phase IP) and the signal that is out of phase (the quadrature, Q) with the external perturbation [264]. These quantities can be represented at each 

Precious, or oriental, cat s eye is the rarest and most highly prized form of chrysoberyl it is a green mineral called cymophane the chatoyant effect is due to parallel arrays of pores. 

FIGURE 36.14 Chatoyancy the scattering of light by aligned fibers or precipitates. 

FIGURE 36.16 The origin of opalescence Bragg scattering of light from a surface of ordered spheres. Best known in opals. 

Iridescence. The best known form of iridescence is opalescence. The reason opals show different colors when viewed in different directions is that the silica spheres are 

FIGURE 36.17 Laboradite causes an iridescence due to scattering by twin planes in the feldspar crystal. 

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A clear, comprehensive discussion of the many facets of nonlinear optics. The emphasis is on optical effects, such as hannonic generation. The treatment of nonlinear spectroscopy, although occupying only a fraction of the book, is clear and physically well-motivated. 

Figure Bl.5.5 Schematic representation of the phenomenological model for second-order nonlinear optical effects at the interface between two centrosynnnetric media. Input waves at frequencies or and m2, witii corresponding wavevectors /Cj(co and k (o 2), are approaching the interface from medium 1. Nonlinear radiation at frequency co is emitted in directions described by the wavevectors /c Cco ) (reflected in medium 1) and /c2(k>3) (transmitted in medium 2). The linear dielectric constants of media 1, 2 and the interface are denoted by E2, and s, respectively. The figure shows the vz-plane (the plane of incidence) withz increasing from top to bottom and z = 0 defining the interface.

Heinz T F 1991 Second-order nonlinear optical effects at surfaces and interfaces Noniinear Surfaoe... 

Reider G A and Heinz T F 1995 Second-order nonlinear optical effects at surfaces and interfaces recent advances Photonio Probes of Surfaoes ed P Halevi (Amsterdam Elsevier) pp 413-78... 

P. N. Prasad andD. J. ITrmis,Introduction tolAonlinear Optical Effects in Molecules and Polymers, Wiley-Interscience, New York, 1990. 

A varnish is often appHed on top of the paint layers. A varnish serves two purposes as a protective coating and also for an optical effect that enriches the colors of the painting. A traditional varnish consists of a natural plant resin dissolved or fused in a Hquid for appHcation to the surface (see Resins, natural). There are two types of varnish resins hard ones, the most important of which is copal, and soft ones, notably dammar and mastic. The hard resins are fossil, and to convert these to a fluid state, they are fused in oil at high temperature. The soft resins dissolve in organic solvents, eg, turpentine. The natural resin varnishes discolor over time and also become less soluble, making removal in case of failure more difficult (see Paint and FINNISH removers). Thus the use of more stable synthetic resins, such as certain methacrylates and cycHc ketone resins, has become quite common, especially in conservation practice. 

Certain glass-ceramic materials also exhibit potentially useful electro-optic effects. These include glasses with microcrystaUites of Cd-sulfoselenides, which show a strong nonlinear response to an electric field (9), as well as glass-ceramics based on ferroelectric perovskite crystals such as niobates, titanates, or zkconates (10—12). Such crystals permit electric control of scattering and other optical properties. 

Optical parametric oscillators (OPOs) represent another tunable soHd-state source, based on nonlinear optical effects. These have been under development for many years and as of this writing (ca 1994) are beginning to become commercially available. These lasers may be tuned by temperature or by rotating a crystal. Models available cover a broad wavelength range in the visible and infrared portions of the spectmm. One commercial device may be tuned from 410 to 2000 nm. 

A wide variety of other nonlinear optical effects also have been demonstrated. According to equation 12, if two light beams having frequency CO and CO2 are combined in a material with a nonzero value of light waves of frequency + UJ2 and are produced. A combination of such effects, used... 

If a modest number of cross-links between the polymer backbone are introduced, the polymer Hquid crystal takes on elastomeric properties. The useflilness of these materials probably Hes in the coupling of mechanical and optical effects. 

Unlike linear optical effects such as absorption, reflection, and scattering, second order non-linear optical effects are inherently specific for surfaces and interfaces. These effects, namely second harmonic generation (SHG) and sum frequency generation (SFG), are dipole-forbidden in the bulk of centrosymmetric media. In the investigation of isotropic phases such as liquids, gases, and amorphous solids, in particular, signals arise exclusively from the surface or interface region, where the symmetry is disrupted. Non-linear optics are applicable in-situ without the need for a vacuum, and the time response is rapid. 

This characteristic of RAIR can be observed experimentally. Fig. 8 shows the transmission spectrum of polydimethylsiloxane (PDMS) while Fig. 9 shows the RAIR spectrum of a thin film of PDMS spin-coated onto a chromium substrate. It can be observed that the bands near 1024 and 1095 cm have similar intensities in the transmission spectra but the band at higher frequencies is clearly much more intense in the RAIR spectrum. This change in relative intensity when PDMS is deposited onto a reflecting substrate is related to optical effects and is not related to orientation effects. 

PLUVUE is a model tliat predicts tlie transport, atmospheric difinsion, chemical conversion, optical effects and surface deposition of point-source emissions. 

Ebert, H. Magneto-optical effects in transition metal systems. Submitted to Reports and Progress in... 

Spontaneous polarization and non-linear optical effect in niobium and tantalum fluoride compounds... 

In this test for transparent plastics, the loss of optical effects is measured when a specimen is exposed to the action of a special abrading wheel. In one type of test the amount of material lost by a specimen is determined when the specimen is exposed to falling abrasive particles or to the action of an abrasive belt. In another test, the loss of gloss due to the dropping of loose abrasive on the specimen is measured. The results produced by the different tests may be of value for research and development work when it is desired to improve a material with respect to one of the test methods. The variables that enter into tests of this type are... 

By its random nature, turbulence does not lend itself easily to modelling starting from the differential equations for fluid flow (Navier-Stokes). However, a remarkably successful statistical model due to Kolmogorov has proven very useful for modelling the optical effects of the atmosphere. 

In astronomy, we are interested in the optical effects of the turbulence. A wave with complex amplitude U(x) = exp[ irefractive index, resulting in a random phase structure by the time it reaches the telescope pupil. If the turbulence is weak enough, the effect of the aberrations can be approximated by summing their phase along a path (the weak phase screen approximation), then the covariance of the complex amplitude at the telescope can be shown to be... 

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