The grating constant is the distance between two scribed lines of the grating, which is expressed by d and is an important parameter of the grating. Usually, the diffraction grating works based on Fraunhofer multi-slit diffraction effect. The formula describing the relationship between grating structure and incident angle and diffraction angle of light is called grating equation.

the grating is composed of a group of many parallel slits with equal width and equal spacing, and it is a combination of single slits. The original grating is carved in parallel on the refined plane optical glass with a diamond cutter. The notch on the grating plays an opaque role, and the gap between the two notches is equivalent to a light-transmitting slit.

Extended information:

Grating is an optical element that uses the principle of multi-slit diffraction to disperse light. It is a flat glass or metal plate engraved with a large number of parallel equal-width and equidistant slits (scribed lines). The number of slits in the grating is very large, generally tens to thousands per millimeter. The diffraction of monochromatic parallel light through each slit of the grating and the interference between slits form a pattern with wide dark stripes and thin bright stripes, which are called spectral lines.

The positions of spectral lines vary with the wavelength. When polychromatic light passes through the grating, spectral lines with different wavelengths appear at different positions to form spectra. The spectrum formed by light passing through grating is the same result of single-slit diffraction and multi-slit interference.

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