Collimated beam

<h2 id="etymology">Etymology</h2>
<p>The word "collimate" comes from the <a href="/facts/Latin/pM3Kge85">Latin</a> verb <i>collimare</i>, which originated in a misreading of <i>collineare</i>, "to direct in a straight line".<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
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<h2 id="sources">Sources</h2>
<h3>Lasers</h3>
<p><a href="/facts/Laser/jk6PTvvT">Laser</a> light from gas or crystal lasers is highly collimated because it is formed in an <a href="/facts/Optical_cavity/BITPG3ga">optical cavity</a> between two parallel <a href="/facts/Mirror/wMu4u6BB">mirrors</a> which constrain the light to a path perpendicular to the surfaces of the mirrors.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> In practice, gas lasers can use concave mirrors, flat mirrors, or a combination of both.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The <a href="/facts/Divergence_(optics)/NVQ2Xmcs">divergence</a> of high-quality laser beams is commonly less than 1 <a href="/facts/Milliradian/vCn6rKUH">milliradian</a> (3.4 <a href="/facts/Arcmin/tybs6YGC">arcmin</a>), and can be much less for large-diameter beams. <a href="/facts/Laser_diode/TjHzJteV">Laser diodes</a> emit less-collimated light due to their short cavity, and therefore higher collimation requires a collimating lens.
</p>
<h3>Synchrotron light</h3>
<p><a href="/facts/Synchrotron_light/mTsSKmRz">Synchrotron light</a> is very well collimated.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> It is produced by bending relativistic electrons (i.e. those moving at <a href="/facts/Special_relativity/vsFFc63E">relativistic</a> speeds) around a circular track. When the electrons are at relativistic speeds, the resulting radiation is highly collimated, a result which does not occur at lower speeds.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
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<h3>Distant sources</h3>
<p>The light from <a href="/facts/Star/PFbd6ICx">stars</a> (other than the <a href="/facts/Sun/CadPCVHh">Sun</a>) arrives at Earth precisely collimated, because stars are so far away they present no detectable angular size. However, due to refraction and turbulence in the Earth's atmosphere, starlight arrives slightly uncollimated at the ground with an <a href="/facts/Astronomical_seeing/TdVzedKJ">apparent angular diameter of about 0.4 arcseconds</a>. Direct rays of light from the Sun arrive at the Earth uncollimated by one-half degree, this being the <a href="/facts/Angular_diameter/p2xv4vcQ">angular diameter</a> of the Sun as seen from Earth.  During a <a href="/facts/Solar_eclipse/2XsCFG1a">solar eclipse</a>, the Sun's light becomes increasingly collimated as the visible surface shrinks to a thin crescent and ultimately a <a href="/facts/Baily%2527s_beads/XtHAMIIL">small point</a>, producing the phenomena of distinct shadows and <a href="/facts/Shadow_bands/tlVCwFnD">shadow bands</a>.
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<h3>Lenses and mirrors</h3>
<p>A perfect <a href="/facts/Parabolic_mirror/uTkv4pJF">parabolic mirror</a> will bring parallel rays to a focus at a single point. Conversely, a point source at the focus of a parabolic mirror will produce a beam of collimated light creating a <a href="/facts/Collimator/UAsMlkeh">collimator</a>. Since the source needs to be small, such an optical system cannot produce much optical power. <a href="/facts/Spherical_mirror/X1c0aVmK">Spherical mirrors</a> are easier to make than parabolic mirrors and they are often used to produce approximately collimated light. Many types of <a href="/facts/Lens_(optics)/ejlH6n5c">lenses</a> can also produce collimated light from point-like sources.
</p><h2 id="collimation-and-decollimation">Collimation and decollimation</h2>
<p>"Collimation" refers to all the optical elements in an instrument being on their designed <a href="/facts/Optical_axis/fKFqnagT">optical axis</a>. It also refers to the process of adjusting an optical instrument so that all its elements are on that designed axis (in line and parallel). The <a href="/facts/Binoculars/DPHVmKIL">unconditional aligning</a> of binoculars is a 3-axis collimation, meaning both optical axis that provide stereoscopic vision are aligned parallel with the axis of the hinge used to select various <a href="/facts/Interpupillary_distance/T7KGYqdD">interpupillary distance</a> settings. With regards to a telescope, the term refers to the fact that the optical axis of each optical component should be centered and parallel, so that collimated light emerges from the eyepiece. Most amateur reflector telescopes need to be re-collimated every few years to maintain optimum performance. This can be done by simple visual methods such as looking down the optical assembly with no eyepiece to make sure the components are lined up, by using a <a href="/facts/Cheshire_eyepiece/NRQd9MuK">Cheshire eyepiece</a>, or with the assistance of a simple laser collimator or <a href="/facts/Autocollimator/B3hB5r9B">autocollimator</a>. Collimation can also be tested using a <a href="/facts/Shearing_interferometer/5j7FfMfv">shearing interferometer</a>, which is often used to test laser collimation.
</p><p>"Decollimation" is any mechanism or process which causes a beam with the minimum possible <a href="/facts/Ray_(optics)/PgUEC7Sm">ray</a> divergence to diverge or converge from parallelism. Decollimation may be deliberate for systems reasons, or may be caused by many factors, such as <a href="/facts/Refractive_index/yjkzvgeE">refractive index</a> inhomogeneities, occlusions, <a href="/facts/Scattering/nMou7lEH">scattering</a>, <a href="/facts/Deflection_(physics)/ya8MwRG3">deflection</a>, <a href="/facts/Diffraction/Mk80xXHT">diffraction</a>, <a href="/facts/Reflection_(physics)/BhcjDs79">reflection</a>, and <a href="/facts/Refraction/S8kvSKzM">refraction</a>. Decollimation must be accounted for to fully treat many systems such as <a href="/facts/Radio/XFr909M2">radio</a>, <a href="/facts/Radar/jk9BTbFA">radar</a>, <a href="/facts/Sonar/0Rg2G40e">sonar</a>, and <a href="/facts/Optical_communication/gshoNBto">optical communications</a>.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Autocollimation/tl2rNPef">Autocollimation</a></li>
<li><a href="/facts/Cross-cockpit_collimated_display/zf7gB62l">Cross-cockpit collimated display</a></li>
<li><a href="/facts/Schlieren_photography/3AosIAbb">Schlieren photography</a></li></ul>

<h2 id="bibliography">Bibliography</h2>
<ul><li>Pfister, J. & Kneedler, J.A. (s.d.). A guide to lasers in the OR.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Introduction to Laser Technology". Melles Griot Catalog (PDF). Melles Griot. n.d. p. 36.6. Retrieved 25 August 2018. <a href="http://file.lasersaur.com/docs-thirdparty/Lasers.pdf" target="_blank">http://file.lasersaur.com/docs-thirdparty/Lasers.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Collimators for Nuclear Medicine". Nuclear Fields. <a href="http://www.nuclearfields.com/collimators-nuclear-medicine.htm" target="_blank">http://www.nuclearfields.com/collimators-nuclear-medicine.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Lewis, Charlton T.; Short, Charles (2010) [1879]. "collimo". A Latin Dictionary. Oxford; Medford: Clarendon Press; Perseus Digital Library. <a href="https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:entry=collimo" target="_blank">https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:entry=collimo</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Properties of Lasers". World of Lasers. 2015. Retrieved 5 August 2015. <a href="http://www.worldoflasers.com/laserproperties.htm" target="_blank">http://www.worldoflasers.com/laserproperties.htm</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Joshi (2010). Engineering Physics. Tata McGraw-Hill Education. p. 517. ISBN 9780070704770. <a href="9780070704770" target="_blank">9780070704770</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Engineering Physics 1: For WBUT. India: Pearson Education India. n.d. pp. 3–9. ISBN 9788131755938. <a href="9788131755938" target="_blank">9788131755938</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Tipler, Paul (1992). Elementary Modern Physics. MacMillan. p. 149. ISBN 9780879015695. <a href="9780879015695" target="_blank">9780879015695</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Winick, Herman; Doniach, S (2012). Synchrotron Radiation Research. Springer Science & Business Media. p. 567. ISBN 9781461579984. <a href="9781461579984" target="_blank">9781461579984</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Mobilio, Settimio; Boscherini, Federico; Meneghini, Carlo (2014). Synchrotron Radiation: Basics, Methods, and Applications. Springer. p. 31. ISBN 9783642553158. <a href="9783642553158" target="_blank">9783642553158</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
</ol>

Collimated beam open-in-new

Collimated beam