Collimated beam: Difference between revisions
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==Sources== |
==Sources== |
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===Lasers=== |
===Lasers=== |
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[[Laser]] light from gas or crystal lasers is highly collimated because it is formed in an [[optical cavity]] between two parallel mirrors which constrain the light to a path perpendicular to the surfaces of the mirrors.<ref>{{cite web |url=http://www.worldoflasers.com/laserproperties.htm |title=Properties of Lasers |author=<!--Staff writer(s); no by-line.--> |date=2015 |website=World of Lasers |publisher=World of Lasers |access-date=5 August 2015}}</ref> In practice, gas lasers |
[[Laser]] light from gas or crystal lasers is highly collimated because it is formed in an [[optical cavity]] between two parallel mirrors which constrain the light to a path perpendicular to the surfaces of the mirrors.<ref>{{cite web |url=http://www.worldoflasers.com/laserproperties.htm |title=Properties of Lasers |author=<!--Staff writer(s); no by-line.--> |date=2015 |website=World of Lasers |publisher=World of Lasers |access-date=5 August 2015}}</ref> In practice, gas lasers can use concave mirrors, flat mirrors, or a combination of both.<ref>{cite book |last=Joshi |date=2010 |title=Engineering Physics |publisher=Tata McGraw-Hill Education |page=517 |isbn=9780070704770 |access-date=6 August 2015 }}</ref><ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |title=Engineering Physics 1: For WBUT |location=India |publisher=Pearson Education India |page=3-9 |date=n.d. |isbn=9788131755938 |access-date=6 August 2015 }}</ref><ref>{{cite book |last=Tipler |first=Paul |date=1992 |title=Elementary Modern Physics |publisher=MacMillan |page=149 |isbn=9780879015695 |access-date=6 August 2015 }}</ref> The divergence of high-quality laser beams is commonly less than 1 milliradian, and can be much less for large-diameter beams. [[Laser diode]]s emit less-collimated light due to their short cavity, and therefore higher collimation requires a collimating lens. |
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===Synchrotron light=== |
===Synchrotron light=== |
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Revision as of 07:12, 6 August 2015
 | This article needs additional citations for verification. (April 2008) |
Collimated light ([ˈkɒɫɨˌmɛɪ̯tɨd])[1] is light whose rays are parallel, and therefore will spread minimally as it propagates. The word is related to "collinear" and implies light that does not disperse with distance (ideally), or that will disperse minimally (in reality). A perfectly collimated beam, with no divergence, cannot be created due to diffraction.[2] 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 wavefronts become flatter and closer to plane waves, which are perfectly collimated.
Etymology
The word "collimate" comes from the Latin verb collimare, which originated in a misreading of collineare, "to direct in a straight line".[3]
Sources
Lasers
Laser light from gas or crystal lasers is highly collimated because it is formed in an optical cavity between two parallel mirrors which constrain the light to a path perpendicular to the surfaces of the mirrors.[4] In practice, gas lasers can use concave mirrors, flat mirrors, or a combination of both.[5][6][7] The divergence of high-quality laser beams is commonly less than 1 milliradian, and can be much less for large-diameter beams. Laser diodes emit less-collimated light due to their short cavity, and therefore higher collimation requires a collimating lens.
Synchrotron light
Synchrotron light is very well collimated. It is produced by bending relativistic electrons (i.e. those moving at relativistic speeds) around a circular track.
Distant sources
The light from stars (other than the Sun) can be considered collimated for almost any purpose, because they are so far away they have almost no angular size. Light from the Sun is nearly collimated by the time it reaches Earth because of its distance from the Earth.[8]
Lenses and mirrors
A perfect parabolic mirror 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 Collimator. Since the source needs to be small, such an optical system cannot produce much optical power. Spherical mirrors are easier to make than parabolic mirrors and they are often used to produce approximately collimated light. Many types of lenses can also produce collimated light from point-like sources.
Collimated displays in flight simulators
This principle is used in Full Flight Simulators (FFS), that have specially designed systems for displaying imagery of the Out-The-Window (OTW) scene to the pilots in the replica aircraft cabin.
In aircraft where two pilots are seated side by side, if the OTW imagery were projected in front of the pilots on a screen, one pilot would see the correct view but the other would see a view where some objects in the scene would be at incorrect angles.
To avoid this, collimated optics are used in the simulator visual display system so that the OTW scene is seen by both pilots at a distant focus rather than at the focal distance of a projection screen. This is achieved through an optical system that allows the imagery to be seen by the pilots in a mirror that has a vertical curvature, the curvature enabling the image to be seen at a distant focus by both pilots, who then see essentially the same OTW scene without any distortions.
This is shown diagrammatically in more detail in the entry on Full Flight Simulators.
Collimation and decollimation
"Collimation" refers to all the optical elements in an instrument being on their designed optical axis. 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). 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 Cheshire eyepiece, or with the assistance of a simple laser collimator or autocollimator. Collimation can also be tested using a shearing interferometer, which is often used to test laser collimation.
"Decollimation" is any mechanism or process which causes a beam with the minimum possible ray divergence to diverge or converge from parallelism. Decollimation may be deliberate for systems reasons, or may be caused by many factors, such as refractive index inhomogeneities, occlusions, scattering, deflection, diffraction, reflection, and refraction. Decollimation must be accounted for to fully treat many systems such as radio, radar, sonar, and optical communications.
See also
References
- ^ "collimate" in Webster's New Collegiate Dictionary (1977), Springfield, MA: Merriam.
- ^ "Introduction to Laser Technology" (PDF). Lasersaur. Melles Griot. n.d. Retrieved 5 August 2015.
- ^ Lewis, Charlton T.; Short, Charles (2010) [1879]. "collimo". A Latin Dictionary. Oxford; Medford: Clarendon Press; Perseus Digital Library.
- ^ "Properties of Lasers". World of Lasers. World of Lasers. 2015. Retrieved 5 August 2015.
- ^ {cite book |last=Joshi |date=2010 |title=Engineering Physics |publisher=Tata McGraw-Hill Education |page=517 |isbn=9780070704770 |access-date=6 August 2015 }}
- ^ Engineering Physics 1: For WBUT. India: Pearson Education India. n.d. p. 3-9. ISBN 9788131755938.
{{cite book}}:|access-date=requires|url=(help) - ^ Tipler, Paul (1992). Elementary Modern Physics. MacMillan. p. 149. ISBN 9780879015695.
{{cite book}}:|access-date=requires|url=(help) - ^ Sliney, David; Mellerio, J (2013). afety with Lasers and Other Optical Sources: A Comprehensive Handbook. Springer Science & Business Media. p. 1. ISBN 9781489935960.
{{cite book}}:|access-date=requires|url=(help)
Bibliography
- Pfister, J. & Kneedler, J.A. (s.d.). A guide to lasers in the OR.