DIFFRACTION GRATING

an optical device that produces orderly diffraction of light, ussaly for use in spectroscopy. Precission optical grantings are made by ruling many thousand of fine, unformly spaced grooves with a diamond point of flat glass plate. The glass may be used directly as a transmission grating or coated with alumunium or silver for used reflection granting. A spectrogarph consists of a reflection granting ruled on aconcave sphericalsurface; it requires no other optical part.
from Encyclopedia International.