Linear birefringence

In these cases, a variation of the distance between the sample and the detector, in which the variation of the detector acceptance angle is also examined, provides an easier diagnosis on the distortion of the CD resulting from the linear birefringence, linear dichroism, and light-scattering effects. 

Fig. 61. Refractive indices at a light wavelength of 1.3 Jim, birefringence, linear coefficient of thermal expansion, and dielectric constant of 6FDA PMDA-TFDB copolymer as a function of the 6FDA content. Reproduced with permission from Macromolecules 1993 26 419 and 1994 27 6665. 1993/1994 American Chemical Society [204,205].

Let us consider investigation of stresses in a 3-D specimen. It has been shown [1] that in the case of weak birefringence a 3-D specimen can be investigated in a conventional transmission polariscope as if it were a two dimensional specimen. On every ray of light it is possible to determine the parameter of the isoclinic and the optical path difference A. The latter are related to the components of the stress tensor on the ray by linear integral relationships... 

To simplify FECO evaluation, it is conmion practice to experimentally filter out one of the components by the use of a linear polarizer after the interferometer. Mica bireftingence can, however, be useftil to study thin films of birefringent molecules [49] between the surfaces. Rabinowitz [53] has presented an eigenvalue analysis of birefringence in the multiple beam interferometer. 

EO effects can be linear or quadratic, depending on whether the degree of phase retardation varies with either the first or second power of apphed voltage. The variation of birefringence with potential takes the form... 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

Such curves, illustrated in Figure 7, show no deviations from linearity which could be attributed to strain-induced crystallization. Similarly, birefringence-temperature measurements also carried out at a > au show no deviations from linearity that could be attributed to crystallization, or to other inter-molecular orderings of the network chains. Typical results of this type are shown in Figure 8 (16),... 

Figure 13.4 Illustration of the freezing point, as shown by the variation in diameter and birefringence with distance from the spinneret for (a) branched, and (b) linear (IV, 0.66) PET samples spun at 5400m/min [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning, Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

As this variation is close to linearity in the whole electric field range investigated the P/Q ratio deduced from the birefringence... 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

Phase transitions are not only characterized by atomic or molecular structural changes - they can also be characterized by significant modifications in the microstmcture and domains and at a much larger size scale. One notable example has been recently reported by Glazer et al. [110] using linear birefringence measurements in LiTaOs and LiTa cNbi c03 crystals at high temperature. 

Three common types of electrooptic effects are illustrated in Figure 8 i.e, quadratic and linear birefringence and memory scattering. Also included in the figure is a typical setup required for generating each effect along with the observed behavior shown in terms of light intensity output (I) as a function of electric field (E). 

A second type of behavior existing in the PLZT s is the linear (Pockels) effect which is generally found in high coercive field, tetragonal materials (composition 3), This effect is so named because of the linear relationship between An and electric field. The truly linear, nonhysteretic character of this effect has been found to be intrinsic to the material and not due to domain reorientation processes which occur in the quadratic and memory materials. The linear materials possess permanent remanent polarization however, in this case the material is switched to its saturation remanence, and it remains in that state. Optical information is extracted from the ceramic by the action of an electric field which causes linear changes in the birefringence, but in no case is there polarization reversal in the material. 

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