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These values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, as is conventionally done. A few examples are given in the adjacent table. Historyįor visible light most transparent media have refractive indices between 1 and 2. Historically air at a standardized pressure and temperature has been common as a reference medium. The definition above is sometimes referred to as the absolute refractive index or the absolute index of refraction to distinguish it from definitions where the speed of light in other reference media than vacuum is used. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves. The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 7008299792458000000♠299 792 458 m/s, and the phase velocity v of light in the medium, In this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen. It can also be used with wave phenomena such as sound.
SOPRA REFRACTIVE INDEX DATABASE FULL
The concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. The imaginary part then handles the attenuation, while the real part accounts for refraction. Light propagation in absorbing materials can be described using a complex-valued refractive index. This is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. The refractive index varies with the wavelength of light. This implies that vacuum has a refractive index of 1, and that the frequency ( f = v/ λ) of the wave is not affected by the refractive index. The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/ n, and similarly the wavelength in that medium is λ = λ 0/ n, where λ 0 is the wavelength of that light in vacuum. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection and Brewster's angle. Where θ 1 and θ 2 are the angles of incidence and refraction, respectively, of a ray crossing the interface between two media with refractive indices n 1 and n 2. This is the first documented use of refractive indices and is described by Snell's law of refraction,
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The refractive index determines how much light is bent, or refracted, when entering a material.