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It is simply represented as n 2 and is called the absolute refractive index of medium 2. The absolute refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299 792 458 m/s, and the phase velocity v of light in the medium, =.
Refraction of light at the interface between two media of different refractive indices, with n 2 > n 1. Since the velocity is lower in the second medium (v 2 < v 1), the angle of refraction θ 2 is less than the angle of incidence θ 1; that is, the ray in the higher-index medium is closer to the normal.
In the context of electromagnetics and optics, the frequency is some function ω(k) of the wave number, so in general, the phase velocity and the group velocity depend on specific medium and frequency. The ratio between the speed of light c and the phase velocity v p is known as the refractive index, n = c / v p = ck / ω.
n 1 = refractive index of initial medium; ... following simply from other definitions of refractive index, wave phase velocity, and the luminal speed equation:
The OPD can be calculated from the following equation: = where d 1 and d 2 are the distances of the ray passing through medium 1 or 2, n 1 is the greater refractive index (e.g., glass) and n 2 is the smaller refractive index (e.g., air).
It is possible to calculate the group velocity from the refractive-index curve n(ω) or more directly from the wavenumber k = ωn/c, where ω is the radian frequency ω = 2πf. Whereas one expression for the phase velocity is v p = ω/k, the group velocity can be expressed using the derivative: v g = dω/dk. Or in terms of the phase velocity v p,
The refractive index of a material is defined as the ratio of c to the phase velocity v p in the material: larger indices of refraction indicate lower speeds. The refractive index of a material may depend on the light's frequency, intensity, polarization, or direction of propagation; in many cases
The ratio between the speed of light c and the phase velocity v p is known as the refractive index, n = c / v p = ck / ω. In this way, we can obtain another form for group velocity for electromagnetics. Writing n = n(ω), a quick way to derive this form is to observe