The total reflection of a beam of light at the interface of one medium and another medium of lower refractive index, when the angle of incidence to the second medium exceeds a specific critical angle.
If a beam of light passing through a medium A (say glass) strikes the boundary to a medium B of lower refractive index (say air) with a small angle of incidence i, part will be refracted, with an angle of refraction r, and part will be reflected. If i is increased it will reach a critical angle c, at which r=90°. If i is now increased further, no refraction can occur and all the light energy is reflected by the interface. This total internal reflection occurs when c (given by nsinc=1) is exceeded (n is the refractive index of A relative to B). The critical angle of optical glass is usually about 40° and total internal reflection is made use of by incorporating prisms in some optical instruments instead of mirrors.
Total internal reflection.
The reflection of a seismic wave from the boundary between the layer in which it is travelling and an adjacent layer. A wave in a low-velocity medium which strikes the inner surface of a boundary with a higher-velocity medium at an angle greater than the critical angle, and therefore is wholly reflected within the layer, is partially converted into another type of wave at the interface, rather than being refracted out of the layer. See s-wave.
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