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(physics) An echelle grating.

Echelle spectrometer: The first standard grating is optimized for a single lower order, while multiple higher orders of the echelle have an optimized output intensity. Both diffractive elements are mounted orthogonally in such a way that the highly illuminated orders of the echelle are transversally separated. Since only parts of the full spectrum of each individual order lie in the illuminated region, only portions of the different orders overlap spectrally (i.e. green line in red portion).