prisms used for the spatial separation of radiations of various.wavelengths. Such prisms are used mainly in spectral instruments. The separation of radiation in a dispersing prism is a result of the dependence of the angle of deflection δ of a ray that has passed through the prism on the index of refraction n, which varies with the wavelength λ. The quality of a dispersion prism is characterized by its angular dispersion, Δδ/Δλ, which depends on the prism material (that is, on the values of n and Δn/Δλ), the angle of refraction α, and the angle of incidence i1:
The choice of material for a dispersing prism depends on the spectral region being studied. Typical materials include flint glass for the visible region, crystalline quartz and fluorite for the ultraviolet region, and lithium fluoride and sodium chloride for the infrared region.