Birefringence effect

Scheffer T J, Nehring J, Kaufmann M, Amstutz H, Heimgartner D and Eglin P 1985 24 80 character LCD panel using the supertwisted birefringence effect Dig. Tech. Papers Int. Symp. Soc. Information Display 16 120-3... 

Two crossed polarizers are frequently used to inspect transparent materials placed between them for optical activity, either for birefringence or for optical rotary effects. Birefringence effects are produced by materials with a regular ordered structure that allows light to pass through at one orientation at a higher velocity than at another orientation. As a result of this, the two wave trains generated by the different velocities... 

What molecular process creates the birefringence effect seen in some injection molded polycarbonate parts ... 

As has been pointed out (63), this is a rather artificial model and, moreover, its application is quite unnecessary. In fact, (a> can be calculated from the refractive index increment (dnjdc), as has extensively been done in the field of light scattering. This procedure is applicable also to the form birefringence effect of coil molecules, as the mean excess polarizability of a coil molecule as a whole is not influenced by the form effect. It is still built up additively of the mean excess polarizabilities of the random links. This reasoning is justified by the low density of links within a coil. In fact, if the coil is replaced by an equivalent ellipsoid consisting of an isotropic material of a refractive index not very much different from that of the solvent, its mean excess polarizability is equal to that of a sphere of equal volume [cf. also Bullough (145)]. 

For the determination of the birefringence effect, polarizer and analyzer are turned by an angle of 45° in their fittings. In this way, the maximum phase difference caused by the total reflection on the mirror device, is added to the phase difference caused by the flowing polymer. This mirror effect, however, can simply be subtracted. It can be calculated with the aid of an exact theory and it can also be measured, when the plate is at rest. For further details the original paper should be inspected (17). 

Extensive work investigating the stress-optical rule has also been performed on polymer solutions [101]. Here the rule can be successfully applied if the solvent contributions to the birefringence are properly subtracted. Care must be taken, however, to avoid form birefringence effects if there is a large refractive index contrast between the polymer and the solvent. 

The super birefringent effect (SBE-LCD) reported by Scheffer and Nehring from Brown Boveri in Baden, Switzerland, uses the optical interference of two normal, elliptically polarised modes of transmitted light generated by a high-tilt, highly-twisted nematic structure viewed between two polarisers set in an unusual way, i.e. the input polarisation direction is not parallel to the nematic director at either substrate surface and the polarisers are not crossed at 90°, see Figure 3.10. 

Figure 3.11 Schematic representation of a super birefringent effect (SBE) LCDJ ...

Figure 3 The experimental setup. A type II Spontaneous parametric down-conversion is used both to produce the ancilla pair (in the spatial modes <23 and a4) and to produce the two input qubits (in the spatial modes ai and 0,2). In this case initial entanglement polarization is not desired, and it is destroyed by making the photons go through polarization filters which prepare the required input state. Half-wave plates have been placed in the photon paths in order to rotate the polarization compensators are able to nullify the birefringence effects of the non-linear crystal and of the polarizing beam splitters. Overlap of the wavepackets at the PBSs is assured through spatial and spectral filtering.

The electric light scattering effect of /3-FeOOH suspension, stabilized by NaCMC adsorption [12], resembles the electric birefringence effect of aqueous NaCMC with close charge density of the macromolecules (Figure 6). Since the NaCMC solution with concentration 2 X 10 2 g dm-3 gives a very weak scattered intensity, the electric birefringence data of Ookubo et... 

Problems that may be encountered due to external birefringence effects in the anisotropic absorption method of Shank and Ippen have been discussed. In the event of these interferences being unavoidable, methods have been described to allow the rotational reorientation times of the dye molecules in fluid solution to be determined. ... 

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