Refractive index of glass

For an air/glass interface, tan 0b = n, the refractive index of glass. In a gas laser, the light must be reflected back and forth between mirrors and through the gas container hundreds of times. Each time the beam passes through the cavity, it must pass through transparent windows at the ends of the gas container (Figure 18.10b), and it is clearly important that this transmission be as efficient as possible. 

In the glass (qv) and ceramic industry (see Ceramics), barite can be used both as a flux, to promote melting at a lower temperature or to increase the production rate, and as an additive to increase the refractive index of glass. The viscosity of barite-containing glass often needs to be raised. Alumina in the form of feldspar is sometimes used. To offset any color produced by iron from the barite addition, more decolorizer may be needed. When properly used, barytes help reduce seed, increase toughness and brilliancy, and reduce annealing time. Barite is also a raw material for the manufacture of other barium chemicals. 

The fact that the optical properties of materials can be altered by a strong electric field was noted by John Kerr in 1875. For example, while glass is normally isotropic, when an electric field is applied, the refractive index of glass becomes anisotropic so that it has different values along the field direction and perpendicular to it. A similar behavior was noted by Friedrich Pockels in 1893 for certain crystals that did not have a center of symmetry in their structure. 

FIG. 126. Density and refractive index of glasses in the system Na20—Si02 (Morey and Merwin, 1932). 

Since the refractive index of glass is increased by intensive laser radiation given by the non-linear refractive index n2 (n = no + n2 , with no = index in absence of intense radiation, E = the electric field strength of the light beam) its magnitude should be as small as possible to avoid self-focussing of the laser beam. 

Repeatability of the technological effects of diffusion manufacturing processes of gradient changes in the refractive index of glasses... 

While the densities of crystalline materials are not particularly sensitive to the thermal history of the sample, densities of glasses are always dependent upon the thermal history of the particular sample measured. Although the differences in density which result from changes in thermal history are not particularly large, they can be very important in certain applications, especially those requiring highly reproducible values of the refractive index of glasses. 

Since the ionic refractivity depends on the polarizability of the ion, large values are found for the large, low field strength ions such as TT and Pb ". Variations in the ionic refractivity explain many of the major trends in the refractive index of glasses. 

The effect of water content on density and refractive index of glasses is much smaller than for Tg and viscosity. The density of vitreous silica decreases by 0.003 g cm while the refractive index decreases by 0.0001 for an increase of 600 wtppm of water, for glasses with identical fictive temperatures. 

The refractive index of glass depends on the density of the material also, so that a change in the volume through thermally induced relaxation of the glass will lead to a change An. The refractive index n is shown as ... 

E1976-98 Standard Test Method for the Auto-mated Determinaton of Refractive Index of Glass Samples Using the Oil Immersion Method... 

Table 6-1 compares the refractive index values of different materials. Note that the refractive index of plastic materials is very close to the refractive index of glass. Two basic methods are most commonly employed to determine the index of refraction. The first method, known as the refractometric method, requires the use of a refractometer. An alternate method calls for the use of a microscope with a magnification power of at least 200 diameters. The refractometric method is generally... 

Notes It is important to remove as much of the PBS as possible because the refractive index of the mounting media (1.515) is designed to match the refractive index of glass (PBS has a much lower refractive index). 

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