diffraction grating

Polished metallic surface (usually a metallic mirror on a block of glass or quartz) or plastic surface on which has been ruled a great number (in thousands) of thin, parallel lines with small gaps between them, used to split light to produce a spectrum.

A beam of light travelling through the narrow gaps of a diffraction grating will spread out and be split into the constituent wavelengths of the light. This is known as diffraction. White light passing through a diffraction grating will be split into the spectrum of colours (from red to blue) of which the light is made up. The light is split because each of its constituent wavelengths (colours) is diffracted by a different amount. Red light, having a longer wavelength, is diffracted more than blue light, having a shorter wavelength.

Some diffraction gratings can have from 2,000 to 7,000 lines per inch.