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High-index: 1.60 ≤ n d < 1.74; Very high index: 1.76 ≤ n d; This is a general classification. Often for marketing purposes, materials with n d values that are at or above 1.60 can be referred to as "high-index". Likewise, Trivex and other borderline normal / mid-index materials may be referred to as mid-index.
A typical polymer has a refractive index of 1.30–1.70, but a higher refractive index is often required for specific applications. The refractive index is related to the molar refractivity, structure and weight of the monomer. In general, high molar refractivity and low molar volumes increase the refractive index of the polymer. [1]
Many materials have a well-characterized refractive index, but these indices often depend strongly upon the frequency of light, causing optical dispersion. Standard refractive index measurements are taken at the "yellow doublet" sodium D line, with a wavelength (λ) of 589 nanometers.
The shortest wavelength's index is , and the longest's is . Abbe numbers are used to classify glass and other optical materials in terms of their chromaticity . For example, the higher dispersion flint glasses have relatively small Abbe numbers V < 55 {\displaystyle V<55} whereas the lower dispersion crown glasses have larger Abbe numbers.
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00.
According to the official census of 2010, Cuba's population was 11,241,161, comprising 5,628,996 men and 5,612,165 women. [316] Its birth rate (9.88 births per thousand population in 2006) [ 317 ] is one of the lowest in the Western Hemisphere .
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