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In optics, a dispersive prism is a type o optical prism, normally having the shape o a geometrical triangular prism. It isthe most widely-known type o optical prism, although perhaps not the most common in actual use. riangular prismsare used to disperse light, that is to break light up into its spectral components. Tis dispersion occurs because the angleo reraction is dependent on the reractive index, which in turn is dependent on the wavelength. Tis eect can alsobe used to measure the reractive index o the prism’s material with high accuracy. In such a measurement, the prism is

placed on the central rotary platorm o an optical spectrometer with the incident light beam adjusted such that thereracted beam is at minimum deviation. Te reractive index can then be computed using the apex angle and the angleo minimum deviation.

A good mathematical description single-prism dispersion is given by Born and Wol.Te case o multiple-prism dispersion is treated by Duarte.

Although the reractive index is dependent on the wavelength in every material, some materials have a much more pow-erul wavelength dependence (are much more dispersive) than others. Crown glasses such as BK7 have a relatively smalldispersion, while fint glasses have a much stronger dispersion (or visible light) and hence are more suitable or use indispersive prisms. Fused quartz is used in the ultraviolet as normal glasses lose their transparency there.

Te top angle o the prism (the upper corner in the accompanying picture) can be chosen to infuence the exact disper-sion characteristics. However, it is typically chosen such that both the incoming and outgoing light rays hit the suraceapproximately at the Brewster angle, so that refection losses are minimized. An example is the use o this type o prismsin prism compressors or generation o ultraast laser pulses.

Te prism is also seen on the cover o Pink Floyd’s Te Dark Side o the Moon. Te graphic on the album cover showsthe ray o light remaining white while passing through the prism and reracting to the entire visible light spectrum onlyupon leaving the prism. Tis image is inaccurate because the dierent wavelength o dierent colors o light cause themto reract as soon as they enter the prism. Te light then creates lights in the designated places.

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