Electro-optical measurements

Polarized microscopy is particularly powerful when combined with electrical measurements on liquid crystal films (known as electro-optical measurements). From microscopic observations of the birefringence in a material as a function of different applied fields, changes in molecular orientation can be inferred, and it is possible to deduce the mechanisms by which the liquid crystal molecules respond to electric or magnetic fields. It is most common to look at the effects of the electric fields on liquid crystal materials. Although magnetic fields will also result in molecular reorientation, the effect is much weaker and therefore has not been commercially useful. 

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Porschke D and Obst A 1991 An electric field jump apparatus with ns time resolution for electro-optical measurements at physiological salt concentrations Rev. Sc/. Instnim. 62 818-20... 

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

Electro-optical measurements at 1.3K. b Direct measurements of tunneling splitting. 

Chen A, Chuyanov V, Garner S, Steier WH, Dalton LR (1997) Modified attenuated total reflection for the fast and routine electro-optic measurements of nonlinear optical polymer films. In Organic thin films for photonic applications, vol 14. Optical Society of America, Washington DC,p 158... 

The experimental value of r, , also agrees fairly well with the predicted value of 48 pm that was calculated from by using a two-level model suggested by Katz and Singer et al. [33], after accounting for dispersion effects from both the EFISH and electro-optic measurements. The r, , is expressed as ... 

Here a) is the optical frequency used in the EFISH measurement, co is the frequency adopted in the electro-optic measurement, and cOq is the transition energy between the ground state and first excited state of the chromophore. 

Watanabe H, Yoshida M, Kikuchi K, Maekawa T. What is the polarizability observed in electro-optical measurements In Jennings BR, Stoylov SP, eds. Colloid and Molecular Electro-Optics. Briston, Philadelphia IOP, 1992 61-70. 

In the latter two phases backbones have the spindle-like conformation, i.e., the prolate shape with (R%) > R p), the characteristic of main chain liquid crystalline polymers. Important means of investigating the conformations of side chain liquid crystalline polymers include small angle neutron scattering from deuterium-labeled chains (Kirst Ohm, 1985), or small angle X-ray scattering on side chain liquid crystalline polymers in a small molecular mass liquid crystal solvent (Mattossi et al., 1986), deuterium nuclear resonance (Boeffel et al., 1986), the stress- or electro-optical measurements on crosslinked side chain liquid crystalline polymers (Mitchell et al., 1992), etc. Actually, the nematic (or smectic modifications) phases of the side chain liquid crystalline polymers have been substantially observed by experiments. 

In the case of pure electrical measurements for substrates and contact materials Au, Ag, or Pt are preferred due to the p-type behaviour of as-prepared oligothiophenes. If simple band models are assumed for otnT and the contacts, materials like the noble metals with a workfunction of 5.3 eV (Au) or 5.6 eV (Pt) should lead to ohmic contacts whereas materials with low workfunction such as Al (4.28 eV) or Mg (3.66 eV) should form Schottky barriers. (For n-type behaviour, i.e. after n-doping or annealing in air, compare Section 4.2.2, the opposite is true.) Both types of contacts are necessary for electro-optical measurements. Here also one electrode has to be optically transparent. The most common material for the latter purpose is indium-oxide doped tin-oxide (ITO). This material is highly transparent and highly conductive but has the problem that the substrate always exhibits several spikes standing out of the surface. The other type of semi-transparent electrodes are ultra-thin metal films evaporated onto the organic film. 

Nonlinear optical properties. The optical nonlinearity was characterized by two experiments second harmonic generation (SHG) and electro-optic measurements. All of the results are listed in Table n. The second harmonic generation (SHG) for the poled polyimides was conducted to determine the second harmonic generation coefficients (das). PI 1 possessed the highest value of SHG... 

The electro-optical measurements were carried out using an electro-optical cell described by Talroze, et al. which was mounted on a heating stage of a polarizing microscope, MIN-8. A photo-element was used in conjunction with a recorder to monitor the transmitted light intensity. The film thickness was about 12 pm, electric field intensity was 10 V/cm. The pleochroic dye for studying the guest host effect had an absorption band at 505 nm. 

In electro-optical measurements, one determines essentially an electrical dipole moment which is related to the number and the spatial distribution of mobile ions in the vicinity of a colloid surface. This technique - light scattering in the presence of an electrical field - was abundantly us in the investigation of the electrical properties of colloids dispersed in water. Extensive monographs on colloid electro-optics were published (7-2). In recent years, the effect of water soluble polymers on the behaviour of hydrosols (especially colloids of mineral or metallic origin) began to raise interest. Polymers partly because of their large... 

In the case of polyelectrolyte adsorption, the electrical dipole comes from both colloid and polyelectrolyte counterion charges. Electro-optical measurements are likely to provide information on the structure of charged polymers in the adsorbed state. 

Shaldin, Yu, V., and Belogurov, D, A., Determination of nonlinear (quadratic) optical susceptibility of GaAs and GaP from electro-optic measurements, Sov. J. Quantum Electron., 6, 897 (1976). 

Ziari, M., Kalluri, S., Gamer, S., Steier, W. H., Liang, Z., Dalton, L. R., and Shi, Y, Novel electro-optic measurement technique for coplanar electrode poled polymers, Proc. SPIE, 2527, 218-227 (1995). 

Characterization of the microgravity mid terrestrial samples included electro-optic measurements, optical microscopy, and scanning electron microscopy. Electro-optic characterization of the PDLCs samples employed voltage-dependent light transmission. The following equation describes laser light transmission through a PDLC ... 

Figure 7. Schematic diagram of the electro-optic measurement apparatus.

Figure 9.28 illustrates the electro-optic responses observed at two 0 s 0° and 30°, where 0 is the angle between the layer normal and one of the crossed polarizer directions. As shown in Figure 9.28 [92], the electric field dependence of transmittance at 0 = 0° shows the typical thresholdless, hysteresis free, V-shaped switching. From the electro-optic measurements at every 5° of 0, the transmittance T versus 0 was obtained at given electric fields. Figure 9.29(a) shows three examples of T versus 0 curves at applied fields of 0, +6, and 6 V/pm [92]. The transmittance T is described by... 

Fig. 23. Kerr electro-optic measurement system used with liquid and gaseous SF. The single...

Fig. 37. Kerr electro-optic measurements in highly purified water...

Hebner, R.E., 1986, Electro-optical measurement techniques, d "Fast... 

PVK ECZ TNF system estimated with frequency-dependent electro-optic measurements. Response functions measured at the... 

Before giving analytical expressions for the director deformations in Freedericksz cells, we will summarize the magnetic and electrical methods. The advantage of electro-optical measurements is that the cell thickness does not enter the equations and is therefore ruled out as an error source. Furthermore, the electric field can always be considered strictly perpendicular to the sample plane. On the other hand, in the electric method conductivity effects can influence the measurements and exact knowledge of and is required to extract the second elastic constant from the birefringence or capacitance characteristics. Moreover, the electric measurement is restricted... 

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