Single refraction

Randomly distributed dipolar molecules form an isotropic medium characterized by a single refractive index n. When these molecules are more or less aligned in an electric field the medium becomes anisotropic and its optical properties must be described by two refractive indices. The Kerr cell consists of a glass vessel fitted with two parallel optical windows and two metal electrodes (Figure 2.11). The cell contains a liquid or a gas (solids can also be used) when an electric field exists between the electrodes the phase difference between the electric vectors is proportional to the square of the field and to the value of the electrical Kerr constant of the dielectric... 

Compounds belonging to the cubic crystal system have only a single refractive index value, but other systems are anisotropic, so that the crystal is characterized by two or three unique indexes. Hexagonal, rhombohedral, and tetragonal crystals have two unique indexes which are traditionally labeled and for ordinary ray and extraordinary ray . Orthorhombic, monoclinic, and triclinic crystals are characterized by three indexes which are here called n, and n. The table indicates the crystal system for each entry in order to identify the material uniquely. 

Calorific Value and Refractive Index of Natural Gas. In addition to a characteristic density, each substance has its own characteristic refractive index. There is a very strong correlation between the gas density and the refractive index of homologous hydrocarbons, as shown in Figure 5. It is possible to measiue the density of a mixture of different gases because the lefiactive index of a gaseous mixture is equal to the constituent sum of the respective single refractive indices. Thus the calorific value of natural gas can be determined from its... 

Isotropic materials (such as a non-oriented glassy polymer) have a single refractive index n which determines the speed C of light in the material... 

This synthesis was announced in 1967 (396). Since then synthetic opals have become available from Gilson of Switzerland (397). These have the appearance of natural opal and many of the same properties, for example hydrated, density 2.113, refractive index 1.45, singly refractive, amorphous, hardness 6.15 mohs (398). The synthetic black opal is said to be indistinguishable from the natural ones by visual examination. Some difference in fluorescent properties was reported. The method of manufacture is a trade secret of the manufacturing company, Gilem S. A. 

Table 3.36 Typical properties of step-index optical fibers, which are characterized by a single refractive index extending over the entire core up to the core/cladding interface [345].

Observation of samples with the analyzer now inserted reveals other information about a material. With the analyzer set to the crossed polars position (90° to polarizer), particles which remain dark while rotating the stage are termed isotropic and exhibit only a single refractive index. All crystals in the cubic system, some polymers, and unstrained glasses are isotropic and will not affect the light passing through them aside from refraction. The vast majority of samples observed will be anisotropic and will appear white or colored under crossed polars. 

In contrast to the well-known concept of self-assembly, layer multiplying co-extrusion uses foreed-assembly to create thousands of alternating layers of two polymers. Individual layers can be less than 10 nm in thickness. If the layers are thinner than the quarter wavelength (k/4n) of light, they can be characterized by a single refractive index. This paper describes the utilization of polymer nanolayer assemblies in the construction of synthetic GRIN materials. 

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