Ray (optics) 3364761 220196888 2008-06-18T18:51:26Z Ukexpat 70142 Reverted edits by [[Special:Contributions/86.90.123.231|86.90.123.231]] (using [[WP:HG|Huggle]]) In [[optics]], a '''ray''' is an idealized narrow [[beam of light]]. Rays are used to model the propagation of [[light]] through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of [[Ray tracing (physics)|ray tracing]].<ref>{{cite web |url=http://www.zemax.com/kb/articles/23/1/What-is-a-ray/Page1.html |title=What is a ray? |first=Ken |last=Moore |date=2005-07-25 |work=ZEMAX Users' Knowledge Base |accessdate=2008-05-30}}</ref> This allows even very complex optical systems to be analyzed mathematically or simulated by computer. Ray tracing uses approximate solutions to [[Maxwell's equations]] that are valid as long as the [[light wave]]s propagate through and around objects whose dimensions are much greater than the light's [[wavelength]]. Ray theory does not describe phenomena such as [[interference]] and [[diffraction]], which require [[wave optics|wave theory]] (involving the [[Phase (waves)|phase]] of the wave). There are many special rays that are used in optical modelling to analyze an optical system. These are defined and described below, grouped by the type of system they are used to model. ==Interaction with surfaces== [[Image:Rays incident on medium.png|thumb|300px|right|Diagram of rays at a surface]] *An '''incident ray''' is a ray of light that strikes a surface. The angle between this ray and the perpendicular or [[surface normal|normal]] to the surface is the [[angle of incidence]]. *The '''reflected ray''' corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the surface normal and the reflected ray is known as the [[angle of reflection]]. The Law of Reflection says that for a [[Specular reflection|specular]] (non-scattering) surface, the angle of reflection always equals the angle of incidence. *The '''refracted ray''' or '''transmitted ray''' corresponding to a given incident ray represents the light that is transmitted through the surface. The angle between this ray and the normal is known as the [[angle of refraction]], and it is given by [[Snell's Law]]. * If the material is [[birefringence|birefringent]], the refracted ray may split into '''ordinary''' and '''extraordinary rays''', which experience different [[index of refraction|indexes of refraction]] when passing through the birefringent material. {{seealso|Reflection (physics)|Refraction|Absorption (optics)|Birefringence}} ==Optical systems== *A '''meridional ray''' is a ray that is confined to the '''y'''-'''z''' plane, where '''z''' points along the [[optical axis]] of the system, and '''y''' is perpendicular to this axis. *The '''marginal ray''' in an optical system is the meridional ray that starts at the point where the object crosses the optical axis, and touches the edge of the [[aperture stop]] of the system.<ref name=Greivenkamp25>{{cite book | first=John E. | last=Greivenkamp | year=2004 | title=Field Guide to Geometrical Optics | publisher=SPIE | others=SPIE Field Guides vol. '''FG01''' | id=ISBN 0-8194-5294-7 }}, p. 25.</ref> This ray is useful, because it crosses the optical axis again at the locations where an image will be formed. The distance of the marginal ray from the optical axis at the locations of the [[entrance pupil]] and [[exit pupil]] defines the sizes of each pupil (since the pupils are [[image]]s of the aperture stop). *The '''chief ray''' in an optical system is the meridional ray that starts at the edge of the object, and passes through the center of the aperture stop.<ref name=Greivenkamp25>Greivenkamp (2004), p. 25.</ref> This ray crosses the optical axis at the locations of the pupils. As such chief rays are equivalent to the rays in a pinhole camera. The distance between the chief ray and the optical axis at an image location defines the size of the image. The marginal and chief rays together define the [[Lagrange invariant]], which characterizes the throughput or [[etendue]] of the optical system.<ref name=Greivenkamp28>Greivenkamp (2004), p. 28.</ref> *A '''skew ray''' is a ray that originates from an object point in the '''y'''-'''z''' plane, but does not propagate in this plane. Such a ray will intersect the entrance pupil at some arbitrary coordinates (''x<sub>p</sub>'',''y<sub>p</sub>''). *A '''tangential ray''' is a ray that intersects the entrance pupil at ''x<sub>p</sub>''=0. This is just another name for a meridional ray. *A '''sagittal ray''' or '''transverse ray''' is a skew ray that intersects the pupil at ''y<sub>p</sub>''=0. ==Fiber optics== * A '''meridional ray''' is a ray that passes through the [[optical axis|axis]] of an [[optical fiber]]. * A '''[[guided ray]]''', '''bound ray''', or '''trapped ray''' is a ray in a [[multimode optical fiber]], which is confined by the [[Fiber_optics#Principle_of_operation|core]]. For [[Step-index profile|step index fiber]], light entering the fiber will be guided if it makes an angle with the fiber axis that is less than the fiber's [[acceptance angle]]. * A '''leaky ray''' or '''tunneling ray''' is a ray in an optical fiber that geometric optics predicts would [[total internal reflection|totally reflect]] at the boundary between the [[Fiber_optics#Principle_of_operation|core]] and the [[cladding]], but which suffers loss due to the curved core boundary. {{seealso|Numerical aperture}} ==See also== *[[Ray transfer matrix analysis]] *[[Paraxial approximation]] ==References== <references/> [[Category:Geometrical optics]] [[Category:Fiber optics]] [[id:Sinar]] [[fr:Rayon lumineux]] [[lv:Gaismas stars]] [[pl:Promień świetlny]] [[ru:Световой луч]] [[vi:Quang tuyến]] [[uk:Світловий промінь]]