Electro-optic technique

The polarization of ionic atmosphere around a polyelectrolyte molecule has been experimentally studied by dielectric and electro-optical techniques in a wide concentration range. In a solution with no added salt, the polyions have an extended conformation and may entangle with each other. This complicates the interpretation of the counterion polarization, since it has been theoretically analyzed for solutions with no interactions between the... 

ABSTRACT E QcXnc field effects in macromolecular organizations such as proteins, nucleic acids, and membranes frequently involve both chemical-conformational changes and physical-orientational displacements of molecular subgroups. Electro-optic techniques in conjunction with relaxation kinetics in high electric fields provide a tool for the investigation of the complex processes encountered in bioelectric phenomena on the level of macromolecules, membrane fragments, and other cellular units. Whereas Part I covers the thermodynamics of electric field effects, this part deals with practical and theoretical aspects of kinetics and mechanisms in aqueous solutions of macromolecules and membranes. 

In this chapter, we will be describing different electro-optic techniques that have been developed specifically for measurement of the flexocoeffi-cients. In these techniques, an electric field is applied to a nematic liquid crystal in a cell with well-defined boundary treatments. The net torque on the medium, which involves dielectric, elastic and flexoelectric components, is set to zero both in the bulk and at the two surfaces in order to And the equilibrium director configuration if a DC field is applied. In AC techniques, the above torques are balanced with the viscous torque. The optical properties of the medium are in turn calculated for the distorted profiles and compared with experimental measurements. The flexoelectric, and in some... 

P.R. Maheswara Murthy, V.A. Raghunathan and N.V. Madhusudana, An AC electro-optic technique of comparing the two anchoring energies of a hybrid aligned nematic cell, Liq. Cryst. 14(4), 1107-1124, (1993). 

With a short laser pulse, the derivative dTIdt is just a jump, therefore, pyroelectric coefficient y(I) can be easily calculated at any temperature of the nematic phase. An example of the Pj(X) dependence is shown in Fig. 11.26b. The maximum value of e for 5CB is 3.610 CGS (or -12 pC/m). It means that the molecular quadrupole has the form shown in the Inset to the same figure. There are some other methods to find the sum of the flexoelectric coefficients based, e.g., on the electro-optical techniques but they are not as straightforward as the pyroelectric technique. 

The concentration of the suspension was 4x10- g/1 in the electro-optic technique and 4x10 g/1 in the Malvern technique. The pH, unless otherwise specified was 5.5 and the ionic strength 10. Each sample suspension was sonica at 22 KHz for 3 min before the measurement was started. 

Modified Laser-Doppler Anemometry is another alternative method to monitor liquid wicking in a 2D fabric plane based on the Doppler principle. When a laser beam is passed through a flowing liquid, light is scattered by the particles suspended in the liquid. The scattered light is subject to a frequency shift and contains information about the velocity of the particles, which can then be examined by electro-optical techniques. This measurement, therefore, requires the flow medium to be partly transparent and containing particles, that scatter light used this method, to obtain the local velocity of liquid flow in a nonwoven fabric. 

Experiments on transport, injection, electroluminescence, and fluorescence probe the spatial correlation within the film, therefore we expect that their response will be sensitive to the self-affinity of the film. This approach, which we proved useful in the analysis of AFM data of conjugated molecular thin films grown in high vacuum, has never been applied to optical and electrical techniques on these systems and might be an interesting route to explore. We have started to assess the influence of different spatial correlations in thin films on the optical and the electro-optical properties, as it will be described in the next section. 

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

Photoelectrochemical techniques have been utilized to determine the minority (electron) diffusion length (L) and other electrical parameters of p-ZnTe [125] and p-type Cdi-jcZnjcTe alloys [126]. In the latter case, the results for a series of single crystals with free carrier concentration in the range 10 " -10 cm (L = 2-4 xm, constant Urbach s parameter at ca. 125 eV ) were considered encouraging for the production of optical and electro-optical devices based on heterojunctions of these alloys. 

J. A. Valdmanis, Electro-Optic Measurement Techniques for Picosecond Materials, Devices, and Integrated Circuits... 

In video microscopy, for instance, background is normally subtracted using differential interference contrast (DIC) [18]. This technique, which requires a number of manipulations from the user, may now be automated using a new method called polarization-modulated (PMDIC) [19,20], It requires the introduction of a liquid crystal electro-optic modulator and of a software module to handle difference images. PMDIC has been shown to bring improvements in imaging moving cells, which show a low contrast, as well as thick tissue samples. 

As mentioned in this section, the linear Stark effect measurement provides detailed information on noncentrosymmetric molecular orientation. This technique is very helpful for the advanced molecular design of noncentrosymmetric LB films for electro-optic and nonlinear optic applications. 

Historically, the first instrument for the determination of lifetime was a phase fluorometer (designed by Gaviola in 1926) operating at a single frequency. Progress in instrumentation enabled variable modulation frequency by employing a cw laser (or a lamp) and an electro-optic modulator (0.1-250 MHz), or by using the harmonic content of a pulsed laser source (up to 2 GHz). These two techniques will now be described. 

To achieve better control of the poling, we have developed an on-line electro-optic monitoring technique . The technique is based on the accumulated change of the electro-optic response when the domains grow through the crystal from the patterned side to the opposite side. A He-Ne beam polarized 45° to the z-axis is launched along the x-axis of the crystal (figure 9). When an electric field is applied, the output polarization state of... 

Nowadays a large number of functional crystals belongs to the TTB family and presents electro-optic, ferro- piezo- pyroelectric properties (e g. the well-known barium sodium niobate Ba2NaNb50i5 (BNN)). In this work iron and manganese based Kx(lvr%(]Vr )i-xF3 fluorides (0.4solid state reaction and characterised by different diffraction techniques in order to investigate their crystalline stmcture. 

Since the photophoretic force depends on the electromagnetic absorption efficiency Q y , which is sensitive to wavelength, photophoretic force measurements can be used as a tool to study absorption spectroscopy. This was first recognized by Pope et al. (1979), who showed that the spectrum of the photophoretic force on a 10 foa diameter perylene crystallite agrees with the optical spectrum. This was accomplished by suspending a perylene particle in a Millikan chamber with electro-optic feedback control and measuring the photophoretic force as a function of the wavelength of the laser illumination. Improvements on the technique and additional data were obtained by Arnold and Amani (1980), and Arnold et al. (1980) provided further details of their photophoretic spectrometer. A photophoretic spectrum of a crystallite of cadmium sulfide reported by Arnold and Amani is presented in Fig. 11. 

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