Prism (optics)

Dispersive prisms are used to break up light into its constituent spectral colors because the refractive index depends on wavelength; the white light entering the prism is a mixture of different wavelengths, each of which gets bent slightly differently.

Prisms are usually made of optical glass which, combined with anti-reflective coating of input and output facets, leads to significantly lower light loss than metallic mirrors.

The cube can also eliminate etalon effects, back-side reflection and slight beam deflection.

In the visible and UV regions, they have very low losses and their extinction ratio typically exceeds

They may or may not employ total internal reflection; These are typically made of a birefringent crystalline material like calcite, but other materials like quartz and α-BBO may be necessary for UV applications, and others (MgF2, YVO4 and TiO2) will extend transmission farther into the infrared spectral range.

Prisms made of isotropic materials like glass will also alter polarization of light, as partial reflection under oblique angles does not maintain the amplitude ratio (nor phase) of the s- and p-polarized components of the light, leading to general elliptical polarization.

Total internal reflection alters only the mutual phase between s- and p-polarized light.

Total internal reflection in prisms finds numerous uses through optics, plasmonics and microscopy.

A familiar dispersive prism
Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet).