Spectrographs, also called spectroradiometers, are optical instruments which belong to the class of spectrometers. A spectrograph contains a polychromator (a device which can spatially separate different wavelength components of light) and some kind of photodetector for measuring the spectral light intensities. (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.
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