Spectrography

Spectrography is the study and application of acquiring and analyzing electromagnetic spectra with a spectrograph, an optical instrument that disperses light into its component wavelengths and records the resulting spectrum. It is used to infer the composition, physical conditions, and motions of light sources by examining spectral lines, bands, and continua.

A typical spectrograph consists of an entrance slit, a collimator to produce a parallel beam, a dispersive element (most commonly a diffraction grating, or sometimes a prism), focusing optics, and a detector such as a charge-coupled device (CCD) or photomultiplier. The dispersed light is mapped onto the detector, producing a spectrum that can be one- or two-dimensional depending on the design. Spectrographs may be configured for wide-field coverage, high spectral resolution, or high sensitivity, and can be adapted for fiber-fed input or integral-field arrangements.

Principles central to spectrography include dispersion, which separates light by wavelength; spectral resolution, set by factors such as slit width, grating spacing, and detector sampling; and calibration, which converts detector coordinates to wavelength. Data analysis involves correcting for instrumental response, subtracting background, and identifying or fitting spectral features to derive physical parameters.

Types of spectrographs range from prism-based to grating-based systems, with high-resolution echelle configurations used in astronomy. Applications are broad and include astronomical spectroscopy for determining chemical abundances and velocities, laboratory spectroscopy for material identification, plasma diagnostics, atmospheric and planetary remote sensing, and industrial process monitoring.

Historically, spectrography emerged from early spectroscopic techniques in the 19th century and has advanced with modern detectors and calibration methods, enabling precise measurements across science and industry.