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Uniaxial Materials and Components
Published in Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young, Polarized Light and Optical Systems, 2018
Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young
The optic axis of a birefringent material is a direction of propagation in which the light experiences zero birefringence. Uniaxial materials only have a single optic axis, hence the name uniaxial. When light propagates in either direction along the optic axis of uniaxial calcite, the electric field components in the transverse plane with the threefold symmetry of the carbon–oxygen bonds can only experience the ordinary refractive index nO; the two eigenmodes are degenerate. Therefore, the optic axis of a uniaxial material is the extraordinary principal axis.
Physical background
Published in Epifanio G. Virga, Variational Theories for Liquid Crystals, 2018
For an optically uniaxial medium the principal index of refraction relative to the optic axis is called extraordinary, while that relative to any direction orthogonal to the optic axis is called ordinary. They are often denoted by ne and n0, respectively.
Polarimetric Optical Fiber Sensors
Published in Shizhuo Yin, Paul B. Ruffin, Francis T. S. Yu, Fiber Optic Sensors, 2017
The quarter-wave plate changes linearly polarized light incident at an angle 45° to the optic axis into circularly polarized light. In this case the birefringent material introduces a phase difference of π/4 between the two component waves, which combine to give circularly polarized light.
Liquid crystal elastomers: an introduction and review of emerging technologies
Published in Liquid Crystals Reviews, 2018
Sabina W. Ula, Nicholas A. Traugutt, Ross H. Volpe, Ravi R. Patel, Kai Yu, Christopher M. Yakacki
The smectic phases, named after the Greek term for soap, are characterized by both orientational and positional order. That is, mesogens in smectic phases orient themselves in layers in addition to having their long axes pointed in roughly the same direction [23,31]. However, there is no positional order within the individual layers – the mesogens in each layer are free to move around and change positions. These layers can also slide over each other, much like their slippery namesake. Mesogens with long aliphatic tails tend to favor smectic phases. Smectic phases are also more likely to occur with amphiphilic interactions – that is, when the aliphatic and polarizable parts of a mesogen separate [22]. The two most common smectic phases are smectic A and smectic C. In smectic A phases, the director is parallel to the layer normal, as shown in Figure 2, while in smectic C phases, the director is tilted at some angle to the layer normal. Therefore, smectic A phases are uniaxial, while smectic C phases form biaxial crystal structures. Regarding birefringence, a uniaxial material has one optic axis, or direction along which the polarization of light propagating through the material does not change, while a biaxial material has two optic axes. As mentioned previously, it is common for a thermotropic system to display multiple phases as it is heated. The degree of freedom in the mesophase determines the order of the phases – highly ordered phases break down as more energy is added into the system. The smectic A phase occurs at a higher temperature than the smectic C phase, and both smectic phases occur at lower temperatures than the nematic phase [34].
Temperature dependence of 2V angle in biaxial negative and positive nematic lyotropic phases
Published in Phase Transitions, 2019
D. D. Luders, W. S. Braga, O. R. Santos, A. R. Sampaio, N. M. Kimura, M. Simões, A. J. Palangana
We remember that the anisotropic part of the optical susceptibility of these lyotropic nematic materials may be expressed as a function of the optical birefringence () which has been considered as an important macroscopic order parameter [14, 40]. The laboratory frame axes are defined with the boundary surfaces parallel to the 1−2 plane and 3 is the axis normal to the biggest surface of the sample cell, with axis parallel to the length (width) of the cells [14, 30, 41]. Optical birefringence () is positive in an phase and () is negative in an phase, where () is the extraordinary (ordinary) refractive index defined for plane wave traveling in a uniaxial nematic medium with the polarization parallel () or perpendicular (⊥) to the optic axis of the nematic sample. The change of sign of optical birefringence, determined in these uniaxial nematic lyotropic phases, is related to the fact that the hydrocarbon chains of the amphiphile molecules in the phase are oriented parallel to the director; whereas, in the phase, the hydrocarbon chains of the amphiphile molecules are oriented perpendicular to the director [42, 43]. In addition, the () phase presents negative (positive) anisotropy of diamagnetic susceptibility [2–5]. This means that homeotropic (planar) alignment of the () phase can be obtained via magnetic field interaction.