Grating principle
Gratings are also called diffraction gratings. It is an optical element that uses the principle of multi-slit diffraction to disperse light (decompose into a spectrum). It is a piece of flat glass or metal sheet engraved with a large number of parallel equal-width, equidistant slits (engraved lines). The grating has a large number of slits, generally tens to thousands per millimeter. The monochromatic parallel light passes through the diffraction of each slit of the grating and the interference between each slit to form a pattern with wide dark stripes and very thin stripes. These sharp and bright stripes are called spectral lines. The position of the spectral line varies with the wavelength. When the polychromatic light passes through the grating, spectral lines of different wavelengths appear at different positions to form a spectrum. The formation of the spectrum of light through the grating is a common result of single slit diffraction and multiple slit interference.