View source for Engineering:Synchrotron light source

{{Short description|Particle accelerator designed to produce intense x-ray beams}}
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[[Image:SynchrotronLight.jpg|thumb|right|250px|Synchrotron radiation reflecting from a [[Chemistry:Terbium|terbium]] crystal at the Daresbury Synchrotron Radiation Source, 1990]]

A '''synchrotron light source''' is a source of [[Physics:Electromagnetic radiation|electromagnetic radiation]] (EM) usually produced by a [[Physics:Storage ring|storage ring]],<ref>''Handbook on Synchrotron Radiation'', Volume 1a, Ernst-Eckhard Koch, Ed., North Holland, 1983, reprinted at "[http://www-als.lbl.gov/als/science/sci_archive/SRTurns50.html Synchrotron Radiation Turns the Big Five-O] {{webarchive |url=https://web.archive.org/web/20080916062040/http://www-als.lbl.gov/als/science/sci_archive/SRTurns50.html |date=September 16, 2008 }}</ref> for scientific and technical purposes.  First observed in [[Physics:Synchrotron|synchrotron]]s, synchrotron light is now produced by storage rings and other specialized [[Physics:Particle accelerator|particle accelerator]]s, typically accelerating [[Physics:Electron|electron]]s. Once the high-energy electron beam has been generated, it is directed into auxiliary components such as bending magnets and insertion devices (undulators or wigglers) in [[Physics:Storage ring|storage ring]]s and free electron lasers. 
These supply the strong magnetic fields perpendicular to the beam that are needed to stimulate the high energy electrons to emit [[Physics:Photon|photon]]s.

The major applications of synchrotron light are in [[Physics:Condensed matter physics|condensed matter physics]], [[Physics:Materials science|materials science]], [[Biology:Biology|biology]] and [[Medicine:Medicine|medicine]]. A large fraction of experiments using synchrotron light involve probing the structure of matter from the sub-nanometer level of [[Engineering:Electronic structure|electronic structure]] to the [[Micrometre|micrometer]] and millimeter levels important in [[Medicine:Medical imaging|medical imaging]]. An example of a practical industrial application is the manufacturing of microstructures by the [[Physics:LIGA|LIGA]] process.

Synchrotron is one of the most expensive kinds of light source known, but it is practically the only viable luminous source of wide-band radiation in far infrared wavelength range for some applications, such as far-infrared absorption spectrometry.

== Spectral brightness ==

The primary figure of merit used to compare different sources of synchrotron radiation has been referred to as the "brightness", the "brilliance", and the "spectral brightness", with the latter term being recommended as the best choice by the Working Group on Synchrotron Nomenclature.<ref name=mills>{{cite journal |last1=Mills |first1=D. M. |last2=Helliwell |first2=J. R. |last3=Kvick |first3=Å. |last4=Ohta |first4=T. |last5=Robinson |first5=I. A. |last6=Authier |first6=A. |title=Report of the Working Group on Synchrotron Radiation Nomenclature – brightness, spectral brightness or brilliance? |journal=Journal of Synchrotron Radiation |date=1 May 2005 |volume=12 |issue=3 |pages=385 |doi=10.1107/S090904950500796X |pmid=15840926 |url=https://journals.iucr.org/s/issues/2005/03/00/es0344/ |access-date=8 April 2022|doi-access=free }}</ref> Regardless of the name chosen, the term is a measure of the total [[Physics:Flux|flux]] of photons in a given six-dimensional [[Physics:Phase space|phase space]] per unit [[Bandwidth (signal processing)|bandwidth]] (BW).<ref name="nielsen">{{cite book | last = Nielsen | first = Jens | title = Elements of modern X-ray physics | publisher = John Wiley | location = Chichester, West Sussex | year = 2011 | isbn = 9781119970156 }}</ref>

The spectral brightness is given by

: <math>B = \frac{\dot N_\text{ph}}{4 \pi^2 \sigma_x \sigma_y \sigma_{x'} \sigma_{y'} \frac{d\omega}{\omega}},</math>

where <math>\dot N_\text{ph}</math> is the number of photons per second in the beam, <math>\sigma_x</math> and <math>\sigma_y</math> are the [[Root mean square|root mean square]] values for the size of the beam in the axes perpendicular to the beam direction, <math>\sigma_{x'}</math> and <math>\sigma_{y'}</math> are the RMS values for the beam solid angle in the ''x'' and ''y'' dimensions, and <math display="inline">\frac{d\omega}{\omega}</math> is the relative bandwidth, or spread in beam frequency around the central frequency.<ref>{{cite book |last1=Wiedemann |first1=Helmut |title=Particle accelerator physics |date=2007 |publisher=Springer |location=Berlin |isbn=9783540490432 |page=782 |edition=3rd}}</ref> The customary value for bandwidth is 0.1%.{{r|mills}}

Spectral brightness has units of time<sup>−1</sup>&sdot;distance<sup>−2</sup>&sdot;angle<sup>−2</sup>&sdot;(% bandwidth)<sup>−1</sup>.

==Properties of sources==
Especially when artificially produced, synchrotron radiation is notable for its:
* High brilliance, many orders of magnitude more than with X-rays produced in conventional X-ray tubes: 3rd-generation sources typically have a brilliance larger than 10<sup>18</sup> photons·s<sup>−1</sup>·mm<sup>−2</sup>·mrad<sup>−2</sup>/(0.1%BW), where 0.1%BW denotes a bandwidth 10<sup>−3</sup>''ω'' centered around the frequency ''ω''.
* High level of polarization (linear, elliptical or circular).
* High collimation, i.e. small angular divergence of the beam.
* Low emittance, i.e. the product of source cross-section and solid angle of emission is small.
* Wide tunability in energy/wavelength by [[Physics:Monochromatization|monochromatization]] (sub-electronvolt up to the megaelectronvolt range).
* Pulsed light emission (pulse durations at or below one [[Second|nanosecond]], or a billionth of a second)..

==Synchrotron radiation from accelerators==
Synchrotron radiation may occur in accelerators either as a nuisance, causing undesired energy loss in [[Physics:Particle physics|particle physics]] contexts, or as a deliberately produced radiation source for numerous laboratory applications. Electrons are accelerated to high speeds in several stages to achieve a final energy that is typically in the gigaelectronvolt range. The electrons are forced to travel in a closed path by strong magnetic fields. This is similar to a radio antenna, but with the difference that the relativistic speed changes the observed frequency due to the Doppler effect by a factor <math>\gamma</math>. Relativistic Lorentz contraction bumps the frequency by another factor of <math>\gamma</math>, thus multiplying the gigahertz frequency of the resonant cavity that accelerates the electrons into the X-ray range. Another dramatic effect of [[Physics:Special relativity|relativity]] is that the radiation pattern is distorted from the isotropic dipole pattern expected from non-relativistic theory into an extremely forward-pointing cone of radiation. This makes synchrotron radiation sources the most brilliant known sources of X-rays. The planar acceleration geometry makes the radiation linearly polarized when observed in the orbital plane, and circularly polarized when observed at a small angle to that plane.{{Citation needed|date=January 2021}}

The advantages of using synchrotron radiation for spectroscopy and diffraction have been realized by an ever-growing scientific community, beginning in the 1960s and 1970s. In the beginning, accelerators were built for particle physics, and synchrotron radiation was used in "parasitic mode" when bending magnet radiation had to be extracted by drilling extra holes in the beam pipes.  The first [[Physics:Storage ring|storage ring]] commissioned as a synchrotron light source was Tantalus, at the [[Organization:Synchrotron Radiation Center|Synchrotron Radiation Center]], first operational in 1968.<ref>E. M. Rowe and F. E. Mills, Tantalus I: A Dedicated Storage Ring Synchrotron Radiation Source, [http://cdsweb.cern.ch/record/1107919/files/p211.pdf Particle Accelerators], Vol. 4 (1973); pages 211-227.</ref> As accelerator synchrotron radiation became more intense and its applications more promising, devices that enhanced the intensity of synchrotron radiation were built into existing rings. Third-generation synchrotron radiation sources were conceived and optimized from the outset to produce brilliant X-rays. Fourth-generation sources that will include different concepts for producing ultrabrilliant, pulsed time-structured X-rays for extremely demanding and also probably yet-to-be-conceived experiments are under consideration.{{Citation needed|date=January 2021}}

Bending electromagnets in accelerators were first used to generate this radiation, but to generate stronger radiation, other specialized devices – insertion devices – are sometimes employed. Current (third-generation) synchrotron radiation sources are typically reliant upon these insertion devices, where straight sections of the storage ring incorporate periodic magnetic structures (comprising many magnets in a pattern of alternating N and S poles – see diagram above) which force the electrons into a sinusoidal or helical path. Thus, instead of a single bend, many tens or hundreds of "wiggles" at precisely calculated positions add up or multiply the total intensity of the beam.{{Citation needed|date=January 2021}}

These devices are called wigglers or undulators. The main difference between an undulator and a wiggler is the intensity of their magnetic field and the amplitude of the deviation from the straight line path of the electrons.{{Citation needed|date=January 2021}}

There are openings in the storage ring to let the radiation exit and follow a beam line into the experimenters' vacuum chamber. A great number of such beamlines can emerge from modern third-generation synchrotron radiation sources.{{Citation needed|date=January 2021}}

===Storage rings===
The electrons may be extracted from the accelerator proper and stored in an ultrahigh vacuum auxiliary magnetic storage ring where they may circle a large number of times. The magnets in the ring also need to repeatedly recompress the beam against Coulomb ([[Physics:Space charge|space charge]]) forces tending to disrupt the electron bunches. The change of direction is a form of acceleration and thus the electrons emit radiation at GeV energies.{{Citation needed|date=January 2021}}

==Applications of synchrotron radiation==
*Synchrotron radiation of an electron beam circulating at high energy in a magnetic field leads to radiative self-polarization of electrons in the beam ([[Physics:Sokolov–Ternov effect|Sokolov–Ternov effect]]).<ref>{{cite book|author=A. A. Sokolov |author2=I. M. Ternov|publisher=American Institute of Physics |series=Translation Series |editor=C. W. Kilmister|location=New York|title=Radiation from Relativistic Electrons|year=1986|isbn=978-0-88318-507-0}}</ref> This effect is used for producing highly polarised electron beams for use in various experiments.{{Citation needed|date=January 2021}}
*Synchrotron radiation sets the beam sizes (determined by the [[Physics:Beam emittance|beam emittance]]) in [[Physics:Storage ring|electron storage rings]] via the effects of [[Physics:Radiation damping|radiation damping]] and quantum excitation.<ref>[http://www.slac.stanford.edu/pubs/slacreports/slac-r-121.html The Physics of Electron Storage Rings: An Introduction by Matt Sands] {{Webarchive|url=https://web.archive.org/web/20150511011430/http://www.slac.stanford.edu/pubs/slacreports/slac-r-121.html |date=2015-05-11 }}</ref>

== Beamlines ==
[[Image:Schéma de principe du synchrotron.jpg|thumb|250px|Beamlines of ''Soleil'']]
At a synchrotron facility, electrons are usually accelerated by a [[Physics:Synchrotron|synchrotron]], and then injected into a [[Physics:Storage ring|storage ring]], in which they circulate, producing synchrotron radiation, but without gaining further energy. The radiation is projected at a tangent to the electron storage ring and captured by [[Physics:Beamline|beamline]]s. These beamlines may originate at bending magnets, which mark the corners of the storage ring; or insertion devices, which are located in the straight sections of the storage ring. The spectrum and energy of X-rays differ between the two types. The beamline includes X-ray optical devices which control the [[Bandwidth (signal processing)|bandwidth]], photon flux, beam dimensions, focus, and collimation of the rays. The optical devices include slits, attenuators, crystal [[Physics:Monochromator|monochromator]]s, and mirrors. The mirrors may be bent into curves or [[Toroid|toroid]]al shapes to focus the beam. A high photon flux in a small area is the most common requirement of a beamline. The design of the beamline will vary with the application. At the end of the beamline is the experimental end station, where samples are placed in the line of the radiation, and detectors are positioned to measure the resulting [[Physics:Diffraction|diffraction]], scattering or secondary radiation.

==Experimental techniques and usage==
Synchrotron light is an ideal tool for many types of research in [[Physics:Materials science|materials science]], [[Physics:Physics|physics]], and [[Chemistry:Chemistry|chemistry]] and is used by researchers from academic, industrial, and government laboratories. Several methods take advantage of the high intensity, tunable wavelength, collimation, and polarization of synchrotron radiation at beamlines which are designed for specific kinds of experiments. The high intensity and penetrating power of synchrotron X-rays enables experiments to be performed inside sample cells designed for specific environments. Samples may be heated, cooled, or exposed to gas, liquid, or high pressure environments. Experiments which use these environments are called ''in situ'' and allow the characterization of atomic- to nano-scale phenomena which are inaccessible to most other characterization tools. ''In operando'' measurements are designed to mimic the real working conditions of a material as closely as possible.<ref>{{cite journal | last1=Nelson | first1=Johanna | last2=Misra | first2=Sumohan | last3=Yang | first3=Yuan | last4=Jackson | first4=Ariel | last5=Liu | first5=Yijin | last6=Wang | first6=Hailiang | last7=Dai | first7=Hongjie | last8=Andrews | first8=Joy C. | last9=Cui | first9=Yi | last10=Toney | first10=Michael F. |display-authors=5| title=In Operando X-ray Diffraction and Transmission X-ray Microscopy of Lithium Sulfur Batteries | journal=Journal of the American Chemical Society | volume=134 | issue=14 | date=2012-03-30 | doi=10.1021/ja2121926 | pmid=22432568 | pages=6337–6343}}</ref>

===Diffraction and scattering===
X-ray diffraction (XRD) and [[Physics:Scattering|scattering]] experiments are performed at synchrotrons for the structural analysis of [[Chemistry:Crystalline|crystalline]] and [[Physics:Amorphous|amorphous]] materials. These measurements may be performed on [[Physics:Powder diffraction|powders]], single crystals, or thin films. The high resolution and intensity of the synchrotron beam enables the measurement of scattering from dilute phases or the analysis of [[Physics:Residual stress|residual stress]]. Materials can be studied at [[Physics:High pressure|high pressure]] using [[Physics:Diamond anvil cell|diamond anvil cell]]s to simulate extreme geologic environments or to create exotic forms of matter.{{Citation needed|date=January 2021}}
[[Image:010 large subunit-1FFK.gif|thumb|200px|left| Structure of a ribosome subunit solved at high resolution using synchrotron X-ray crystallography.<ref name=Ban2000>{{cite journal | last1=Ban | first1=N. |first2=P. |last2=Nissen|first3=J. |last3=Hansen |first4=P. |last4=Moore|first5= T. |last5=Steitz |title=The Complete Atomic Structure of the Large Ribosomal Subunit at 2.4 Å Resolution | journal=Science | volume=289 | issue=5481 | date=2000-08-11 | doi=10.1126/science.289.5481.905 | pmid=10937989 | pages=905–920| bibcode=2000Sci...289..905B }}</ref>]]

[[Physics:X-ray crystallography|X-ray crystallography]] of [[Biology:Proteins|proteins]] and other macromolecules (PX or MX) are routinely performed. Synchrotron-based crystallography experiments were integral to solving the structure of the [[Biology:Ribosome|ribosome]];<ref name=Ban2000 /><ref>The Royal Swedish Academy of Sciences, [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/popular-chemistryprize2009.pdf "The Nobel Prize in Chemistry 2009: Information for the Public"], accessed 2016-06-20</ref> this work earned the [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/ Nobel Prize in Chemistry in 2009].

The size and shape of nanoparticles are characterized using small angle X-ray scattering (SAXS). Nano-sized features on surfaces are measured with a similar technique, [[Physics:Grazing-incidence small-angle scattering|grazing-incidence small angle X-ray scattering]] (GISAXS).<ref>{{cite journal | last1=Renaud | first1=Gilles | last2=Lazzari | first2=Rémi | last3=Leroy | first3=Frédéric | title=Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering | journal=Surface Science Reports | volume=64 | issue=8 | year=2009 | doi=10.1016/j.surfrep.2009.07.002 | pages=255–380| bibcode=2009SurSR..64..255R }}</ref> In this and other methods, surface sensitivity is achieved by placing the crystal surface at a small angle relative to the incident beam, which achieves [[Physics:Total external reflection|total external reflection]] and minimizes the X-ray penetration into the material.{{Citation needed|date=January 2021}}

The atomic- to nano-scale details of [[Physics:Surface science|surfaces]], interfaces, and thin films can be characterized using techniques such as [[Physics:X-ray reflectivity|X-ray reflectivity]] (XRR) and [[Physics:X-ray crystal truncation rod|crystal truncation rod]] (CTR) analysis.<ref>{{cite journal | last1=Robinson | first1=I K | last2=Tweet | first2=D J | title=Surface X-ray diffraction | journal=Reports on Progress in Physics | volume=55 | issue=5 | date=1992-05-01 | doi=10.1088/0034-4885/55/5/002 | pages=599–651| bibcode=1992RPPh...55..599R | s2cid=250899816 }}</ref> X-ray standing wave (XSW) measurements can also be used to measure the position of atoms at or near surfaces; these measurements require high-resolution optics capable of resolving dynamical diffraction phenomena.<ref>{{cite journal | last1=Golovchenko | first1=J. A. | last2=Patel | first2=J. R. | last3=Kaplan | first3=D. R. | last4=Cowan | first4=P. L. |author5-link=Michael Bedzyk | last5=Bedzyk | first5=M. J. | title=Solution to the Surface Registration Problem Using X-Ray Standing Waves | journal=Physical Review Letters | volume=49 | issue=8 | date=1982-08-23 | doi=10.1103/physrevlett.49.560 | pages=560–563| bibcode=1982PhRvL..49..560G | url=https://dash.harvard.edu/bitstream/1/29407052/1/SolutionToTheSurfaceRegistrationProblem.pdf }}</ref>

Amorphous materials, including liquids and melts, as well as crystalline materials with local disorder, can be examined using X-ray [[Physics:Pair distribution function|pair distribution function]] analysis, which requires high energy X-ray scattering data.<ref>T. Egami, S.J.L. Billinge, "Underneath the Bragg Peaks: Structural Analysis of Complex Materials", [https://books.google.com/books?id=ek2ymu7_NfgC&pg=PP2 ''Pergamon'' (2003)]</ref>

By tuning the beam energy through the [[Physics:Absorption edge|absorption edge]] of a particular element of interest, the scattering from atoms of that element will be modified. These so-called resonant anomalous X-ray scattering methods can help to resolve scattering contributions from specific elements in the sample.{{Citation needed|date=January 2021}}

Other scattering techniques include energy dispersive X-ray diffraction, [[Physics:Resonant inelastic X-ray scattering|resonant inelastic X-ray scattering]], and magnetic scattering.{{Citation needed|date=January 2021}}

===Spectroscopy===
[[Physics:X-ray absorption spectroscopy|X-ray absorption spectroscopy]] (XAS) is used to study the coordination structure of atoms in materials and molecules. The synchrotron beam energy is tuned through the absorption edge of an element of interest, and modulations in the absorption are measured. Photoelectron transitions cause modulations near the absorption edge, and analysis of these modulations (called the [[Physics:X-ray absorption near edge structure|X-ray absorption near-edge structure]] (XANES) or near-edge X-ray absorption fine structure (NEXAFS)) reveals information about the [[Chemistry:Chemical state|chemical state]] and local symmetry of that element. At incident beam energies which are much higher than the absorption edge, photoelectron scattering causes "ringing" modulations called the [[Physics:Extended X-ray absorption fine structure|extended X-ray absorption fine structure]] (EXAFS). Fourier transformation of the EXAFS regime yields the bond lengths and number of the surrounding the absorbing atom; it is therefore useful for studying liquids and [[Physics:Amorphous|amorphous]] materials<ref>{{cite journal | last1=Sayers | first1=Dale E. | last2=Stern | first2=Edward A. | last3=Lytle | first3=Farrel W. | title=New Technique for Investigating Noncrystalline Structures: Fourier Analysis of the Extended X-Ray—Absorption Fine Structure | journal=Physical Review Letters | volume=27 | issue=18 | date=1971-11-01 | doi=10.1103/physrevlett.27.1204 | pages=1204–1207| bibcode=1971PhRvL..27.1204S }}</ref> as well as sparse species such as impurities. A related technique, [[Physics:X-ray magnetic circular dichroism|X-ray magnetic circular dichroism]] (XMCD), uses circularly polarized X-rays to measure the magnetic properties of an element.{{Citation needed|date=January 2021}}

[[Physics:X-ray photoelectron spectroscopy|X-ray photoelectron spectroscopy]] (XPS) can be performed at beamlines equipped with a [[Physics:Photoemission spectroscopy|photoelectron analyzer]]. Traditional XPS is typically limited to probing the top few nanometers of a material under vacuum. However, the high intensity of synchrotron light enables XPS measurements of surfaces at near-ambient pressures of gas. Ambient pressure XPS (AP-XPS) can be used to measure chemical phenomena under simulated catalytic or liquid conditions.<ref>{{cite journal | last1=Bluhm | first1=Hendrik | last2=Hävecker | first2=Michael | last3=Knop-Gericke | first3=Axel | last4=Kiskinova | first4=Maya | last5=Schlögl | first5=Robert | last6=Salmeron | first6=Miquel | title=In Situ X-Ray Photoelectron Spectroscopy Studies of Gas-Solid Interfaces at Near-Ambient Conditions | journal=MRS Bulletin | volume=32 | issue=12 | year=2017 | doi=10.1557/mrs2007.211 | pages=1022–1030| s2cid=55577979 | url=https://digital.library.unt.edu/ark:/67531/metadc900709/ }}</ref> Using high-energy photons yields high kinetic energy photoelectrons which have a much longer [[Physics:Inelastic mean free path|inelastic mean free path]] than those generated on a laboratory XPS instrument. The probing depth of synchrotron XPS can therefore be lengthened to several nanometers, allowing the study of buried interfaces. This method is referred to as high-energy X-ray photoemission spectroscopy (HAXPES).<ref>{{cite journal | last1=Sing | first1=M. | last2=Berner | first2=G. | last3=Goß | first3=K. | last4=Müller | first4=A. | last5=Ruff | first5=A. | last6=Wetscherek | first6=A. | last7=Thiel | first7=S. | last8=Mannhart | first8=J. | last9=Pauli | first9=S. A. | last10=Schneider | first10=C. W. | last11=Willmott | first11=P. R. | last12=Gorgoi | first12=M. | last13=Schäfers | first13=F. | last14=Claessen | first14=R. | title=Profiling the Interface Electron Gas of LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Heterostructures with Hard X-Ray Photoelectron Spectroscopy | journal=Physical Review Letters | volume=102 | issue=17 | date=2009-04-30 | doi=10.1103/physrevlett.102.176805 | page=176805| pmid=19518810 | arxiv=0809.1917 | bibcode=2009PhRvL.102q6805S | s2cid=43739895 }}</ref> Furthermore, the tunable nature of the synchrotron X-ray photon energies presents a wide range of depth sensitivity in the order of 2-50 nm.<ref>{{Cite journal |last1=Gong |first1=Zhengliang |last2=Yang |first2=Yong |date=2018 |title=The application of synchrotron X-ray techniques to the study of rechargeable batteries |url=https://linkinghub.elsevier.com/retrieve/pii/S2095495617311877 |journal=Journal of Energy Chemistry |language=en |volume=27 |issue=6 |pages=1566–1583 |doi=10.1016/j.jechem.2018.03.020|s2cid=104038441 }}</ref> This allows for probing of samples at greater depths and for non destructive depth-profiling experiments.

Material composition can be quantitatively analyzed using [[Physics:X-ray fluorescence|X-ray fluorescence]] (XRF). XRF detection is also used in several other techniques, such as XAS and XSW, in which it is necessary to measure the change in absorption of a particular element.{{Citation needed|date=January 2021}}

Other spectroscopy techniques include angle resolved photoemission spectroscopy (ARPES), [[Physics:Soft X-ray emission spectroscopy|soft X-ray emission spectroscopy]], and [[Nuclear resonance vibrational spectroscopy|nuclear resonance vibrational spectroscopy]], which is related to [[Mössbauer spectroscopy]].{{Citation needed|date=January 2021}}

===Imaging===
[[File:APS - Nanoprobe.jpg|thumb|right|X-ray nanoprobe beamline at the [[Organization:Advanced Photon Source|Advanced Photon Source]]]]
Synchrotron X-rays can be used for traditional X-ray imaging, [[Phase-contrast X-ray imaging|phase-contrast X-ray imaging]], and [[Physics:Tomography|tomography]]. The Ångström-scale wavelength of X-rays enables imaging well below the [[Physics:Diffraction limit|diffraction limit]] of visible light, but practically the smallest resolution so far achieved is about 30&nbsp;nm.<ref>Argonne National Laboratory Center for Nanoscale Materials, [http://www.anl.gov/cnm/capabilities/x-ray-microscopy-capabilities "X-Ray Microscopy Capabilities"], accessed 2016-06-20</ref> Such [[Engineering:Nanoprobe (device)|nanoprobe]] sources are used for [[Scanning transmission X-ray microscopy|scanning transmission X-ray microscopy]] (STXM). Imaging can be combined with spectroscopy such as [[Physics:X-ray fluorescence|X-ray fluorescence]] or [[Physics:X-ray absorption spectroscopy|X-ray absorption spectroscopy]] in order to map a sample's chemical composition or oxidation state with sub-micron resolution.<ref>{{cite journal | last1=Beale | first1=Andrew M. | last2=Jacques | first2=Simon D. M. | last3=Weckhuysen | first3=Bert M. | title=Chemical imaging of catalytic solids with synchrotron radiation | journal=Chemical Society Reviews | volume=39 | issue=12 | year=2010 | pages=4656–4672 | doi=10.1039/c0cs00089b | pmid=20978688 | hdl=1874/290865 | hdl-access=free }}</ref>

Other imaging techniques include [[Engineering:Coherent diffraction imaging|coherent diffraction imaging]].{{Citation needed|date=January 2021}}

Similar optics can be employed for [[Engineering:Photolithography|photolithography]] for [[Engineering:Microelectromechanical systems|MEMS]] structures can use a synchrotron beam as part of the [[Physics:LIGA|LIGA]] process.{{Citation needed|date=January 2021}}

== Compact synchrotron light sources ==
Because of the usefulness of tuneable collimated [[Physics:Coherence|coherent]] X-ray radiation, efforts have been made to make smaller more economical sources of the light produced by synchrotrons. The aim is to make such sources available within a research laboratory for cost and convenience reasons; at present, researchers have to travel to a facility to perform experiments.  One method of making a compact light source is to use the energy shift from [[Physics:Compton scattering|Compton scattering]] near-visible laser photons from electrons stored at relatively low energies of tens of megaelectronvolts (see for example the Compact Light Source (CLS)<ref>{{cite web|url=http://www.eurekalert.org/pub_releases/2006-03/lti-msp030106.php |title=Miniature synchrotron produces first light |publisher=Eurekalert.org |access-date=2009-10-19}}</ref>). However, a relatively low cross-section of collision can be obtained in this manner, and the repetition rate of the lasers is limited to a few hertz rather than the megahertz repetition rates naturally arising in normal storage ring emission. Another method is to use plasma acceleration to reduce the distance required to accelerate electrons from rest to the energies required for UV or X-ray emission within magnetic devices.{{Citation needed|date=January 2021}}

==See also==
*[[Physics:List of synchrotron radiation facilities|List of synchrotron radiation facilities]]
*[[Physics:List of light sources|List of light sources]]

==References==
<references/>

==External links==
*[http://www.elettra.eu/ Elettra Sincrotrone Trieste - Elettra and FERMI lightsources]
* [http://news.bbc.co.uk/2/hi/science/nature/7324564.stm Imaging ancient insects with synchrotron light source -- BBC]
* [http://www.iop.org/publications/iop/2011/page_47511.html Synchrotron light at IOP]

{{DEFAULTSORT:Synchrotron Light Source}}
[[Category:Synchrotron radiation]]
[[Category:Synchrotron-related techniques]]
[[Category:Particle physics]]
[[Category:Light]]
[[Category:Light sources]]
[[Category:Materials testing]]
[[Category:Particle accelerators]]

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