A specialized diffraction grating with widely spaced, deep grooves that operates at high diffraction orders to achieve very high spectral resolution. The coarse groove spacing allows multiple spectral orders to be recorded simultaneously, providing detailed analysis of spectral lines across a broad wavelength range.
From French 'échelle' meaning ladder or scale, referring to the ladder-like appearance of the multiple spectral orders when dispersed. Developed in the 1940s by French physicist Pierre Jacquinot, the term reflects how the overlapping spectral orders create a step-like pattern resembling rungs on a ladder.
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