# Refractive Index

In optics the refractive index (or index of refraction) n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium. Its most elementary occurrence (and historically the first one) is in Snell's law of refraction, n1sinθ1= n2sinθ2, where θ1 and θ2 are the angles of incidence of a ray crossing the interface between two media with refractive indices n1 and n2.

Brewster's angle, the critical angle for total internal reflection, and the reflectivity of a surface also depend on the refractive index, as described by the Fresnel equations.

More fundamentally, n is defined as the factor by which the wavelength and the velocity of the radiation are reduced with respect to their vacuum values: The speed of light in a medium is v = c/n, where c is the speed in vacuum. Similarly, for a given vacuum wavelength λ0, the wavelength in the medium is λ=λ0/n. This implies that vacuum has a refractive index of 1. Historically other reference media (e.g., air at a standardized pressure and temperature) have been common.

Refractive index of materials varies with the wavelength. This is called dispersion; it causes the splitting of white light in prisms and rainbows, and chromatic aberration in lenses. In opaque media, the refractive index is a complex number: while the real part describes refraction, the imaginary part accounts for absorption.

The concept of refractive index is widely used within the full electromagnetic spectrum, from x-rays to radio waves. It can also be used with wave phenomena other than light (e.g., sound). In this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen.

### Other articles related to "refractive index, refractive, index":

Refractive Index - Applications
... The refractive index of a material is the most important property of any optical system that uses refraction ... Since refractive index is a fundamental physical property of a substance, it is often used to identify a particular substance, confirm its purity, or measure its concentration ... Refractive index is used to measure solids (glasses and gemstones), liquids, and gases ...
Slot-waveguide
... strongly confined light in a subwavelength-scale low refractive index region by total internal reflection ... A slot-waveguide consists of two strips or slabs of high-refractive-index (nH) materials separated by a subwavelength-scale low-refractive-index (nS) slot region and surrounded by low-refractive-index (nC ...
Kerr-induced Self-focusing
... radiation, and which produces a variation of the refractive index as described by the formula, where n0 and n2 are the linear and non-linear components ... Since n2 is positive in most materials, the refractive index becomes larger in the areas where the intensity is higher, usually at the centre of a beam, creating a focusing density profile ...
Mathematical Descriptions Of Opacity - Complex Refractive Index, Extinction Coefficient
... Recall that in nonattenuating media, the refractive index and wavenumber are related by A complex refractive index can therefore be defined in terms of the complex wavenumber ... The real part of is often (ambiguously) called simply the refractive index ...
Soliton (optics) - Spatial Solitons
... If we leave the width L fixed in each point, but we change the value of the refractive index we will get exactly the same effect, but with a completely different approach ... That's the way graded-index fibers work the change in the refractive index introduces a focusing effect that can balance the natural diffraction of the field ... effect introduces a Self-phase modulation that changes the refractive index according to the intensity if has a shape similar to the one shown in the figure, then we have created the phase behavior we ...

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