The relative refractive index of an optical medium 2 with respect to another reference medium 1 (n21) is given by the ratio of speed of light in medium 1 to that in medium 2. This … See more

At the atomic scale, an electromagnetic wave's phase velocity is slowed in a material because the electric field creates a disturbance in the charges of each atom (primarily the electrons) proportional to the electric susceptibility of the medium. (Similarly, the See more

When light passes through a medium, some part of it will always be absorbed. This can be conveniently taken into account by defining a … See more

Optical path length
Optical path length (OPL) is the product of the geometric length d of the path light follows through a system, and the index of refraction of the medium through which it propagates, $${\text{OPL}}=nd.$$ This is an important … See more

Thomas Young was presumably the person who first used, and invented, the name "index of refraction", in 1807. At the same time he changed this value of refractive power into … See more

Refractive index also varies with wavelength of the light as given by Cauchy's equation. The most general form of this equation is $${\displaystyle n(\lambda )=A+{\frac {B}{\lambda ^{2}}}+{\frac {C}{\lambda ^{4}}}+\cdots ,}$$ where n is the … See more

The refractive index of materials varies with the wavelength (and frequency) of light. This is called dispersion and causes prisms and rainbows to divide white light into its constituent … See more