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Definition: instruments for spectrally analyzing light

Alternative term: spectroradiometers

German: Spektrographen

Categories: general optics, light detection and characterization, optical metrology

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Spectrographs, also called spectroradiometers, are optical instruments which belong to the class of spectrometers. A spectrograph contains a device which can spatially separate different wavelength components of light (based e.g. on a diffraction grating) and measure their intensities with some kind of photodetector. (Early versions of spectrographs used photographic plates for recording spectra.) That way one can measure the optical spectrum of a light source.

The operation principles of spectrographs are explained in the article on spectrometers.

Note that optical spectra can also be measured in different ways, for example with scanning spectrometers. Those can work with a single photodetector instead of a multi-channel detector (e.g. a photodiode array), as required for a spectrograph.

Applications of Spectrographs

Some typical applications of spectrographs are:

  • Stellar and solar spectrographs are used for analyzing in detail the radiation from stars. For example, one can measure the locations and strengths of certain absorption lines (Fraunhofer lines) for measuring chemical compositions and relative velocities.
  • With a laboratory spectrograph, one may spectrally analyze fluorescence light e.g. from gas discharges or from active optical fibers.
  • In spectral phase interferometry, one often requires a spectrograph for measuring the positions of minima and maxima in optical spectra. An intensity calibration is often not required.
  • Spectrographs are also used for other methods of pulse characterization, for example for frequency-resolved optical gating.


The RP Photonics Buyer's Guide contains 12 suppliers for spectrographs.

See also: spectrometers, optical spectrum, laser beam characterization
and other articles in the categories general optics, light detection and characterization, optical metrology


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