crossdispersed

Crossdispersed is an adjective used in spectroscopy and related instrumentation to describe systems, data, or configurations that implement cross dispersion—a method in which light dispersed by a primary disperser is subsequently spread in a perpendicular direction by a secondary dispersive element. The arrangement is designed to separate spectral orders along one axis while keeping wavelength information on the other, enabling higher resolution and broader spectral coverage in a single exposure.

In a typical cross-dispersed echelle spectrograph, light first passes through an echelle grating that produces many overlapping orders. A cross-disperser (often a prism or a low-dispersion grating) is oriented perpendicular to the main dispersion, spreading the orders across a two-dimensional detector such as a CCD. The resulting image shows multiple orders arranged along one axis and wavelength within each order along the other.

Crossdispersed instruments are common in astronomy for optical and near-infrared spectroscopy and in laboratory spectroscopy where wide spectral coverage is desired. They contribute to high spectral resolution with broad coverage compared to single-dispersion configurations.

Data from crossdispersed systems appear as two-dimensional spectra. Reduction involves order tracing, wavelength calibration, blaze correction, flat-fielding, and order merging. The complexity of alignment and throughput losses are important design considerations.

Terminology: The term is often written as cross-dispersed or cross dispersion rather than as a single word; some sources may use crossdispersed as a compound adjective. Its precise meaning depends on context but generally refers to the use of a secondary dispersive element perpendicular to the primary dispersion.