crossdisperser

A crossdisperser is an optical element used in cross-dispersed spectrographs to separate spectral orders along a direction perpendicular to the primary dispersion produced by the main dispersive element, typically an echelle grating. By spreading the orders in the orthogonal axis, it enables the recording of a two-dimensional spectrum on a single detector with wide wavelength coverage and high resolution.

In a cross-dispersed setup, light first encounters the main disperser, which creates multiple spectral orders that would otherwise overlap when projected onto the detector. The crossdisperser then disperses these orders in the perpendicular direction, separating them so that individual orders appear as distinct stripes or bands on the detector. Common implementations include prism-based crossdispersers, grating-based crossdispersers (grisms), or combinations of prisms and gratings. The choice of design depends on the target spectral range, desired resolution, and instrument throughput.

Design considerations for crossdispersers focus on dispersion, throughput, and spectral coverage, as well as optical quality across the field and wavelength dependence. Material choice for prisms (such as fused silica or other optical glasses) and coatings affects efficiency and stray light. Alignment stability and calibration are important to maintain accurate wavelength mapping across orders.

Crossdispersers are used in both astronomical and laboratory spectroscopy. In astronomy, they are integral to high-resolution, wide-coverage instruments that study stellar spectra, planetary atmospheres, and distant galaxies. In laboratory settings, cross-dispersed spectrometers support chemical analysis and material characterization where detailed spectral information over broad ranges is required.