Optical Anisotropy


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optical anisotropy

[′äp·tə·kəl ‚an·ə′sä·trə·pē]
(optics)
The behavior of a medium, or of a single molecule, whose effect on electromagnetic radiation depends on the direction of propagation of the radiation.

Optical Anisotropy

 

the difference in the optical properties of a medium as a function of the direction of propagation of optical radiation (light) in the medium and of the state of polarization of the radiation. Optical anisotropy, especially in crystal optics, is frequently understood to mean only the phenomenon of double refraction. However, it is more correct to also classify rotation of the plane of polarization, which occurs in optically active substances, as optical anisotropy.

The natural optical anisotropy of most crystals is due to the character of their structure (the difference in different directions of the field of forces binding the particles in the crystal lattice) and, in the case of some optically active crystals, also to the peculiarities of the excited state of the electrons and “ion cores” in the crystals. The natural optical activity (rotation of the plane of polarization) of substances that manifest it in any state of aggregation (crystalline, amorphous, liquid, or gaseous) is related to the asymmetric structure of the individual molecules of the substances and to the differences—resulting from this asymmetry—in the interactions of the molecules with variously polarized radiation.

Induced (artificial) optical activity arises in media that are by nature optically isotropic, upon exposure to external fields that single out certain directions in the media. These may be an electric field (the Kerr effect), a magnetic field (the Cotton-Mouton and Faraday effects), or a field of elastic forces (the phenomenon of photoelasticity). Double refraction in a fluid flow (the Maxwell effect) and in media through which light fluxes of superhigh intensity (usually laser radiation) are transmitted is also classified as artificial optical anisotropy.

S. G. PRZHIBEL’SKII

References in periodicals archive ?
As pointed out by Wu and Van Der Giessen [5, 8], the three-chain model tends to overestimate the optical anisotropy and the mechanical response at large stretch, relative to the Intermediate network model, while the eight-chain model tends to underestimate it.
The mechanical and optical anisotropy developed in polymeric materials at large strains are governed by the evolution of molecular orientation during deformation and have been found to be highly dependent on the state of deformation.
The mechanical anisotropy increases with increasing rolled ratio which is in good agreement with the optical anisotropy results.
Together, Eqs 2, 3, and 4 completely describe the optical anisotropy of the medium for generalized stretch states.
The elasticity of the entire network is found by summing contributions of forces on all chains in the network analogously to the manner in which the total network optical anisotropy was established earlier.

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