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Echelle

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Echelle 

(also echelle grating), a diffraction grating of the reflection type that concentrates the energy of diffracted radiation in spectra of fifth to 500th order (seeORDER OF INTERFERENCE). When the number of grooves is relatively small (10–100 lines per mm), echelles are characterized by a very high dispersion and a very high resolving power. As a dispersing element, the echelle has parameters that are intermediate between those of the Michelson reflection echelon and the echelette.

The profile of the grooves of an echelle is the same as that of the grooves of an echelette. The blaze angle, or the angle of inclination of the mirror surface of a groove, may be as high as 75°.

Echelles are used in high-resolution monochromators and in cross-dispersion spectrographs. For example, the STE-I spectrograph contains a prism and an echelle whose spectrum scanning planes are mutually perpendicular.
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I used to sleep at Echelles, in a manger full of straw.
The Country Doctor by de Balzac, Honore View in context
He had brought his two nephews, Laurent and Gabriel, from Echelles in Savoie,--one to serve the heads of the bureaus, the other the director himself.
Bureaucracy by de Balzac, Honore View in context
 
 
 
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