Editing Collimated beam (section)

{{Short description|Light all pointing in the same direction}}
[[Image:Collimator2.svg|thumb|In the lower picture, the light has been collimated.]]

A '''collimated beam''' of [[light]] or other [[electromagnetic radiation]] has parallel [[ray (optics)|rays]], and therefore will spread minimally as it propagates. A [[laser beam]] is an archetypical example. A perfectly collimated [[light beam]], with no [[beam divergence|divergence]], would not disperse with distance. However, [[diffraction]] prevents the creation of any such beam.<ref>{{cite book |url=http://file.lasersaur.com/docs-thirdparty/Lasers.pdf |title=Melles Griot Catalog |chapter=Introduction to Laser Technology |author=<!--Staff writer(s); no by-line--> |page=36.6 |date=n.d. |publisher=Melles Griot |access-date=25 August 2018}}</ref>

Light can be approximately collimated by a number of processes, for instance by means of a [[collimator]]. Perfectly collimated light is sometimes said to be ''focused at infinity''. Thus, as the distance from a point source increases, the spherical [[wavefront]]s become flatter and closer to [[plane wave]]s, which are perfectly collimated.

Other forms of electromagnetic radiation can also be collimated. In [[radiology]], [[X-rays]] are collimated to reduce the volume of the patient's tissue that is irradiated, and to remove stray photons that reduce the quality of the x-ray image ("film fog"). In [[scintigraphy]], a gamma ray collimator is used in front of a detector to allow only photons perpendicular to the surface to be detected.<ref>{{cite web |url=http://www.nuclearfields.com/collimators-nuclear-medicine.htm |title=Collimators for Nuclear Medicine |publisher=Nuclear Fields}}</ref>

The term ''collimated'' may also be applied to [[particle beam]]s – a '''collimated particle beam''' – where typically shielding blocks of high density materials (such as [[lead]], [[woods metal|bismuth alloys]], etc.) may be used to absorb or block peripheral particles from a desired forward direction, especially a sequence of such absorbing [[collimator]]s. This method of particle collimation is routinely deployed and is ubiquitous in every [[particle accelerator]] complex in the world. An additional method enabling this same forward collimation effect, less well studied, may deploy strategic nuclear polarization ([[magnetization|magnetic polarization]] of nuclei) if the requisite reactions are designed into any given experimental applications.