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. This allows even very complex optical systems to be analyzed mathematically or simulated by computer eggs eggs eggs. Table of Opticks, 1728 Cyclopaedia Optics ( appearance or look in ancient Greek) is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. ... 20th Century Fox logo with two visible light beams; see that article for other versions of the logo A light beam or beam of light is a narrow cone of light energy radiating from a small source. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength[1]. The elementary particle that defines light is the photon. ... A ray traced scene. ...

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

• An incident ray is a ray of light that strikes a surface. The angle between this ray and the perpendicular or 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 (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 birefringent, the refracted ray may split into ordinary and extraordinary rays, which experience different indexes of refraction when passing through the birefringent material.

See also: Reflection (physics), Refraction, Absorption (optics), and Birefringence

A surface normal, or just normal to a flat surface is a three-dimensional vector which is perpendicular to that surface. ... Fig. ... An angle of incidence is the angle between a beam incident on a surface and the normal (line perpendicular to the surface at the point of incidence). ... Diagram of specular reflection Specular reflection is the perfect, mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected onto a single outgoing direction. ... Angle of refraction refers to the angle a wave makes to the line of normal incidence when a wave passes from one medium to another. ... Refraction of light at the interface between two media of different refractive indices, with n2 > n1. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... Spheres reflecting the floor and each other. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... Absorption, in optics, is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on...

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 it.
• 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. 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 images 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. This ray crosses the optical axis at the locations of the pupils. The distance between the chief ray and the optical axis at an image location defines the size of the image.
• 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_p,y_p).
• A tangential ray is a ray that intersects the entrance pupil at x_p=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_p=0.

In telecommunication, the term optical axis has the following meanings: 1. ... In optics, an aperture is something which restricts the diameter of the light path through one plane in an optical system. ... In an optical system, the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light. ... The exit pupil is a concept in optics, and is defined as the minimum diameter of the light beam leaving an eyepiece though which all of the light from the eyepiece passes. ... In common usage, an image (from Latin imago) or picture is an artifact that reproduces the likeness of some subject—usually a physical object or a person. ...

Fiber optics

• A meridional ray is a ray that passes through the 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 core. For 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 totally reflect at the boundary between the core and the cladding, but which suffers loss due to the curved core boundary.

See also: Numerical aperture

In telecommunication, the term optical axis has the following meanings: 1. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by total internal reflection. ... Guided ray: In an optical fiber, a ray that is confined primarily to the core. ... Multimode optical fiber is has two characteristics that allow it support more than one propagation mode, or path within the fiber. ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... For an optical fiber, a step-index profile is refractive index profile characterized by a uniform refractive index within the core and a sharp decrease in refractive index at the core-cladding interface. ... In optical fibers the acceptance angle θ is the half-angle of the cone within which incident light is totally internally reflected by the fiber core. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... The term cladding can have a number of meanings: Regarding optical fiber in telecommunication, cladding is one or more layers of material of lower refractive index, in intimate contact with a core material of higher refractive index. ... Numerical aperture is a technical term of multiple uses: Numerical aperture of optical telecommunication fiber Numerical aperture in microscopy This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

See also

• Ray transfer matrix analysis
• Paraxial approximation

Ray transfer matrix analysis (also known as ABCD matrix analysis) is a type of ray tracing technique used in the design of some optical systems, particularly lasers. ... In geometric optics, the paraxial approximation is an approximation used in ray tracing of light through an optical system (such as a lens). ...

References

• Greivenkamp, John E. (2004). Field Guide to Geometrical Optics, SPIE Field Guides vol. FG01, SPIE. ISBN 0-8194-5294-7.