abstract:An echelle grating (from French, échelle, meaning stairs or ladder) is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at a high incidence angle and therefore in high diffraction orders. Echelle gratings are, like other types of diffraction grating, used in spectrometers and similar instruments.
The generaltheories behind echelleand its applicationsinastronomy are briefed, and thedifferences betweenechellespectrographandplanegrating spectrograph are analyzedandcompared.