![]() When a beam is incident on a grating with an angle θ i (measured from the normal of the grating), it is diffracted into several beams. This is visually similar to the operation of a prism, although the mechanism is very different. Each wavelength of input beam spectrum is sent into a different direction, producing a rainbow of colors under white light illumination. Therefore, a grating separates an incident polychromatic beam into its constituent wavelength components, i.e., it is dispersive. In that case, the groove density can vary from a few tens of grooves per millimeter, as in echelle gratings, to a few thousands of grooves per millimeter.Ī fundamental property of gratings is that the angle of deviation of all but one of the diffracted beams depends on the wavelength of the incident light. In the optical regime, in which the use of gratings is most common, this corresponds to wavelengths between 100 nm and 10 µm. The groove period must be on the order of the wavelength in question. Gratings are usually designated by their groove density, the number of grooves per unit length, usually expressed in grooves per millimeter (g/mm), also equal to the inverse of the groove period. This was similar to notable German physicist Joseph von Fraunhofer's wire diffraction grating in 1821. The principles of difraction gratings were discovered by James Gregory (astronomer and mathematician), about a year after Newton's Prism experiments, initially with artefacts such as bird feathers.The first man-made diffraction grating was made around 1785 by Philadelphia inventor David Rittenhouse, who strung hairs between two finely threaded screws. More precisely, a single wavelength can simultaneously have multiple discrete diffraction angles, called diffraction orders. Because of their ability of splitting light into different wavelengths (dispersion), gratings are commonly used in monochromators and spectrometers.įor a given grating, light with a larger wavelength generally has a larger diffraction angle. Such gratings can be either transparent or reflective. However, for practical applications, most gratings have grooves or rulings on their surface rather than dark lines. ![]() In its simplest form, a diffraction grating could be a photographic slide with a fine pattern of black lines. This diffraction angle depends on the wavelength of the light. Light rays that pass through such a surface are bent as a result of diffraction, related to the wave properties of light. In optics, a diffraction grating is an optical component with a surface covered by a regular pattern of parallel lines, typically with a distance between the lines comparable to the wavelength of light.
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