laser crystals) in the visible spectral region are in the range from 1.4 to 2.8, and typically the refractive index increases for shorter wavelengths. Typical refractive index values for glasses and crystals (e.g. The refractive index of a material depends on the optical frequency or wavelength this dependency is called chromatic dispersion. Wavelength Dependence and Others Dependencies For usual optical materials, is close to unity. Note that the values of and at the optical frequency have to be used, which can deviate substantially from those at low frequencies. The refractive index can be calculated from the relative permittivity and the relative permeability of an optical material: The wavelength of light in the medium is times smaller than the vacuum wavelength.
Via the phase velocity, the refractive index also determines phenomena such as refraction, reflection and diffraction at optical interfaces see the article on Fresnel equations. with low optical intensities) of plane waves. Here, one assumes linear propagation (i.e. The refractive index of a transparent optical medium, also called the index of refraction, is the factor by which the phase velocity is decreased relative to the velocity of light in vacuum:
