Birefringence optic sign

We do not observe an image of the crystal in the focal plane of the objective of the microscope, but an interference pattern. Each point in this plane corresponds to the direction of a wave normal characterized by a birefringence, and hence, by an interference color or light intensity. The intensity goes to zero for all waves polarized according to the polarizer and the analyzer. The interference figures are characteristic of the crystal symmetry, the optical sign and the orientation of the indicatrix. 

Skillful use of PLM, compensators, and calibrated optics (for measurement) are sufficient to determine the key optical features of a fiber, such as its dimensions, morphology, Rl, birefringence, and sign of elongation, without resorting to multiple mountings and repetitive experiments. 

Such measurement provides the magnitude of birefringence, but not its sign. In addition, identical transmission values will be observed for multiple birefringence orders, that is, whenever the optical path difference, dAn, becomes a multiple of X. The main interest of this method arises from its excellent time resolution, below 1 ms, that is readily achieved using a low-power (e.g., 5 mW) continuous-wave laser and a photodiode. If the sample is initially isotropic, it is possible to follow the birefringence order to obtain quantitative results. For improved accuracy, a second (reference) photodiode or a beam chopper and a lock-in amplifier can be used. 

The electro-optical birefringence in the form (236) with the plus sign defines the result of O Konski et al. for cigar-shaped partides. With minus sign, it defines those of Shah for disc-like ones and of Yoshioka et al. for both cases. 

This formula permits the determination, from birefringence saturation studies, of not only the absolute value of the volume optical anisotropy I 8 I = I I but moreover of its sign, thus revealing to us the shape... 

As already mentioned, the optical anisotropy of a rigid-chain molecule is its second main property determining the value and sign of birefringence observed in solution. It is characterized by the difference between the main optical polarizabilities 7i,... 

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