Absolute temperature coefficient refractive index

The index of refraction is affected by temperature variations. This can be ascertained through the temperature coefficient of refractive index, denoted dn /dT. Hence, the Abbe number also changes with temperature. There are two ways of showing the temperature coefficient of the refractive index. One is the absolute temperature coefficient of refractive index dn ldT), measured in a vacuum, and the other is the relative temperature coefficient of refractive index dn-JdT),, measured in ambient air (101.3 kPa in dry air). They are related by the following formula ... 

Here n is the average refractive index, k is Boltzman s constant, and T is absolute temperature (13). If a polyblend were to form a homogeneous network, the stress would be distributed equally between network chains of different composition. Assuming that the size of the statistical segments of the component polymers remains unaffected by the mixing process, the stress-optical coefficient would simply be additive by composition. Since the stress-optical coefficient of butadiene-styrene copolymers, at constant vinyl content, is a linear function of composition (Figure 9), a homogeneous blend of such polymers would be expected to exhibit the same stress-optical coefficient as a copolymer of the same styrene content. Actually, all blends examined show an elevation of Ka which increases with the breadth of the composition distribution (Table III). Such an elevation can be justified if the blends have a two- or multiphase domain structure in which the phases differ in modulus. If we consider the domains to be coupled either in series or in parallel (the true situation will be intermediate), then it is easily shown that... 

The rapid increase in the thermal conductivity of liquid selenium with temperature can be attributed to the photon component of the thermal conductivity. For liquids with a small absorption coefficient, this radiation term should rise as a third power of the absolute temperature. From the results of the thermal conductivity data we can, therefore, get information about two optical parameters, i.e., the optical absorption coefficient, a, and the refractive index, n, in the form a/n. ... 

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