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Dispersion

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Dispersion

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The primary purpose of a diffraction grating is to disperse light spatially by wavelength. A beam of white light incident on a grating will be separated into its component wavelengths upon diffraction from the grating, with each wavelength diffracted along a different direction. Dispersion is a measure of the separation (either angular or spatial) between diffracted light of different wavelengths. Angular dispersion expresses the spectral range per unit angle, and linear resolution expresses the spectral range per unit length.The angular spread Δβ of a spectrum of order m between the wavelength λ and λ + Δλ can be obtained by differentiating the grating equation, assuming the incidence angle α to be constant.For a given diffracted wavelength λ in order m (which corresponds to an angle of diffraction β), the linear dispersion of a grating system is the product of the angular dispersion D and the effective focal length r'(β) of the system.

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