What are diffraction gratings?

A diffraction grating separates polychromatic (or multiple wavelength) light into its component wavelengths by diffraction. Diffraction is a process in which light incident to a surface with dimensions similar in size to its wavelength is dispersed at certain angles. These diffraction angles are dependent upon the wavelength of light. Thus, polychromatic light will have a separate diffraction angle for each individual wavelength. This difference in diffraction angle is what separates light into its component wavelengths.