Echellegitter

Echellegitter, or echelon grating, is a type of optical diffractive element designed for high-resolution spectroscopy. It consists of a broad, nearly flat reflective surface that has been fabricated into a staircase of shallow steps ( terraces). Each terrace acts as a separate reflective facet with a small tilt, creating a large path difference when light is reflected at grazing incidence. The combination of the large step height and the shallow blaze angle yields an effectively coarse groove spacing, which provides very high spectral dispersion and allows operation in high diffraction orders.

In operation, light interacts with many terraces, and constructive interference selects specific diffraction orders m, yielding very high resolving power. Because the effective groove spacing is large, echelon gratings are typically used at grazing incidence and are often paired with cross-dispersers to separate overlapping spectral orders. They are widely employed in echelle spectrographs, especially in astronomy and atmospheric science, where extremely high resolution is required over a broad wavelength range.

Manufacture and materials: echelon gratings are produced by precise machining or lithographic processes to form a uniform staircase over a substantial aperture. They are usually coated with a reflective metal or dielectric coating to maximize reflectivity in the target spectral band. Proper alignment and mechanical stability are essential, as small deviations can reduce resolution and efficiency. They find use across ultraviolet to mid-infrared wavelengths, depending on substrate and coating choices.

Compared with conventional diffraction gratings, echelon gratings offer very high dispersion in a compact form but may exhibit lower throughput and stricter alignment requirements. Related topics include the echelle spectrograph and diffraction grating.