Refractometer
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A refractometer is a laboratory or field device for the measurement of an index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index of refraction then allows the concentration to be determined using mixing rules such as the Gladstone–Dale relation and Lorentz–Lorenz equation.
Hand-held refractometer
Bausch & Lomb Abbe Refractometer, ca. 1919-1926
Gemology refractometer ER604 used to test light bending in gemstones; courtesy of A.KRÜSS Optronic GmbH
Hand refractometer
Refractive index
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In optics, the refractive index of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
Thomas Young coined the term index of refraction in 1807.
Diamonds have a very high refractive index of 2.417.
A split-ring resonator array arranged to produce a negative index of refraction for microwaves
In optical mineralogy, thin sections are used to study rocks. The method is based on the distinct refractive indices of different minerals.