Editing Optical spectrometer (section)

{{Short description|Instrument to measure the properties of visible light}}
{{hatnote group|
{{Redirect-distinguish|Spectrograph|Spectrogram}}
{{Broader|Photometry (optics)}}
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{{more footnotes needed|date=December 2010}}

[[Image:Spectrometer.svg|thumb|right|300px|Grating spectrometer schematic]]
[[File:Simple_grating_spectrometer_inside.jpg|thumb|right|300px|Internal structure of a grating spectrometer: Light comes from left side and diffracts on the upper middle reflective grating. The wavelength of light is then selected by the slit on the upper right corner.]]

An '''optical spectrometer''' ('''spectrophotometer''', '''spectrograph''' or '''spectroscope''') is an instrument used to measure properties of [[light]] over a specific portion of the [[electromagnetic spectrum]], typically used in [[spectroscopic analysis]] to identify materials.<ref>{{cite journal |first1=L. R. P. |last1=Butler |first2=K. |last2=Laqua |year=1995 |title=Nomenclature, symbols, units and their usage in spectrochemical analysis-IX. Instrumentation for the spectral dispersion and isolation of optical radiation (IUPAC Recommendations 1995) |journal=Pure Appl. Chem. |volume=67 |issue=10 |pages=1725–1744 |doi=10.1351/pac199567101725 |s2cid=94991425 |url=http://iupac.org/publications/pac/67/10/1725/ |quote=A spectrometer is the general term for describing a combination of spectral apparatus with one or more detectors to measure the intensity of one or more spectral bands.|doi-access=free }}</ref> The variable measured is most often the [[irradiance]] of the light but could also, for instance, be the [[Polarization (waves)|polarization]] state. The independent variable is usually the [[wavelength]] of the light or a closely derived physical quantity, such as the corresponding [[wavenumber]] or the [[photon]] energy, in units of measurement such as centimeters, [[reciprocal centimeters]], or [[electron volt]]s, respectively.

A [[spectrometer]] is used in [[spectroscopy]] for producing [[spectral line]]s and measuring their [[wavelength]]s and intensities. Spectrometers may operate over a wide range of non-optical wavelengths, from [[gamma ray]]s and [[X-ray]]s into the [[far infrared]]. If the instrument is designed to measure the spectrum on an [[absolute scale]] rather than a relative one, then it is typically called a [[spectrophotometer]]. The majority of spectrophotometers are used in spectral regions near the visible spectrum.

A spectrometer that is calibrated for measurement of the incident optical power is called a [[spectroradiometer]].<ref>{{cite book |last1=Schneider |first1=T. |last2=Young |first2=R. |last3=Bergen |first3=T. |last4=Dam-Hansen |first4=C |last5=Goodman |first5=T. |last6=Jordan |first6=W. |last7=Lee |first7=D.-H |last8=Okura |first8=T. |last9=Sperfeld |first9=P. |last10=Thorseth |first10=A |last11=Zong |first11=Y. |title=CIE 250:2022 Spectroradiometric Measurement of Optical Radiation Sources |date=2022 |publisher=CIE - International Commission on Illumination |location=Vienna |isbn=978-3-902842-23-7 |url=https://orbit.dtu.dk/en/publications/cie-2502022-spectroradiometric-measurement-of-optical-radiation-s}}</ref>

In general, any particular instrument will operate over a small portion of this total range because of the different techniques used to measure different portions of the spectrum. Below optical frequencies (that is, at [[microwave]] and [[radio]] frequencies), the [[spectrum analyzer]] is a closely related electronic device.

Spectrometers are used in many fields.  For example, they are used in astronomy to analyze the radiation from objects and deduce their chemical composition.  The spectrometer uses a prism or a grating to spread the light into a spectrum.  This allows astronomers to detect many of the chemical elements by their characteristic spectral lines.  These lines are named for the elements which cause them, such as the [[hydrogen alpha]], beta, and gamma lines.  A glowing object will show bright spectral lines.  Dark lines are made by absorption, for example by light passing through a gas cloud, and these absorption lines can also identify chemical compounds.  Much of our knowledge of the chemical makeup of the universe comes from spectra.