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The Littrow configuration is a special geometry in which the blaze angle is chosen such that diffraction angle and incidence angle are identical. [1] For a reflection grating , this means that the diffracted beam is back-reflected into the direction of the incident beam (blue beam in picture).
A blazed diffraction grating reflecting only the green portion of the spectrum from a room's fluorescent lighting. For a diffraction grating, the relationship between the grating spacing (i.e., the distance between adjacent grating grooves or slits), the angle of the wave (light) incidence to the grating, and the diffracted wave from the grating is known as the grating equation.
Diffraction of a laser beam by a grating. A grating is defined in Born and Wolf as "any arrangement which imposes on an incident wave a periodic variation of amplitude or phase, or both". A grating whose elements are separated by S diffracts a normally incident beam of light into a set of beams, at angles θ n given by: [19]
The construction of a master grating is a long, expensive process because the grooves must be of identical size, exactly parallel, and equally spaced over the length of the grating (3–10 cm). A grating for the ultraviolet and visible region typically has 300–2000 grooves/mm, however 1200–1400 grooves/mm is most common.
Visulization of flux through differential area and solid angle. As always ^ is the unit normal to the incident surface A, = ^, and ^ is a unit vector in the direction of incident flux on the area element, θ is the angle between them.
The glancing angle θ (see figure on the right, and note that this differs from the convention in Snell's law where θ is measured from the surface normal), the wavelength λ, and the "grating constant" d of the crystal are connected by the relation: [11]: 1026 = where is the diffraction order (= is first order, = is second order, [10]: 221 ...
Recent advances have seen increasing reliance of computational algorithms in a range of miniaturised spectrometers without diffraction gratings, for example, through the use of quantum dot-based filter arrays on to a CCD chip [3] or a series of photodetectors realised on a single nanostructure.
An echelle grating (from French échelle, meaning "ladder") is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore in high diffraction orders. Higher diffraction orders allow for increased dispersion (spacing) of spectral features at ...