NationMaster - Encyclopedia: Total internal reflection

$The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. (The color of the rays is to help distinguish the rays, and is not meant to indicate any color dependence.)$

The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. (The color of the rays is to help distinguish the rays, and is not meant to indicate any color dependence.)

Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary no light can pass through, so effectively all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs. In this diagram, the black arrow represents the direction of the wind. ... Figure showing total internal reflection of an optical ray. ... Figure showing total internal reflection of an optical ray. ... An optical phenomenon is any observable event which results from the interaction of light and matter. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... The reflection of a bridge in Indianapolis, Indianas Central Canal. ... Fig. ...

When light crosses a boundary between materials with different refractive indices, the light beam will be partially refracted at the boundary surface, and partially reflected. However, if the angle of incidence is greater (i.e. the ray is closer to being parallel to the boundary) than the critical angle — the angle of incidence at which light is refracted such that it travels along the boundary — then the light will stop crossing the boundary altogether and instead be totally reflected back internally. This can only occur where light travels from a medium with a higher refractive index to one with a lower refractive index. For example, it will occur when passing from glass to air, but not when passing from air to glass. For other uses, see Light (disambiguation). ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... For the property of metals, see refraction (metallurgy). ... Fig. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... This article is about the material. ... Air redirects here. ...

1 Optical description
2 Critical angle
3 Frustrated total internal reflection
4 Applications
5 Simple household example
6 See also
7 References
8 External links

Optical description

Total internal reflection

Total internal reflection can be demonstrated using a semi-circular glass block. A "ray box" shines a narrow beam of light (a "ray") onto the glass. The semi-circular shape ensures that a ray pointing towards the centre of the flat face will hit the curved surface at a right angle, this will prevent refraction at the air/glass boundary of the curved surface. At the glass/air boundary of the flat surface, what happens will depend on the angle. Where θ_c is the critical angle (measured normal to the surface): Total internal reflection Taken by fir0002 File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Total internal reflection Taken by fir0002 File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In optics, a ray is an idealized narrow beam of light. ...

If θ < θ_c, as with the red ray in the above figure, the ray will split. Some of the ray will reflect off the boundary, and some will refract as it passes through.
If θ > θ_c, as with the blue ray, the entire ray reflects from the boundary. None passes through. This is called total internal reflection.

This physical property makes optical fibers useful, and rainbows and prismatic binoculars possible. It is also what gives diamonds their distinctive sparkle, as diamond has an extremely high refractive index. Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... For other uses, see Rainbow (disambiguation). ... Porro-prism binoculars with central focusing Binocular telescopes, or binoculars, (also known as field glasses) are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. ... This article is about the mineral. ...

An important side effect of total internal reflection is the propagation of an evanescent wave across the boundary surface. Essentially, even though the entire incident wave is reflected back into the originating medium, there is some penetration into the second medium at the boundary. Additionally, the evanescent wave appears to travel along the boundary between the two materials. This wave can lead to a phenomenon known as frustrated total internal reflection. An evanescent wave is an electromagnetic wave that decays exponentially with distance. ...

Critical angle

The critical angle is the angle of incidence above which total internal reflection occurs. The angle of incidence is measured with respect to the normal at the refractive boundary. The critical angle $θ c$ is given by: A surface normal, or just normal to a flat surface is a three-dimensional vector which is perpendicular to that surface. ...

$theta_c = arcsin left( frac{n_2}{n_1} right),$

where $n 2$ is the refractive index of the less dense medium, and $n 1$ is the refractive index of the denser medium. This equation is a simple application of Snell's law where the angle of refraction is 90°. The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Free space is the most simple and elementary electromagnetic medium. ... Refraction of light at the interface between two media of different refractive indices, with n2 > n1. ...

If the incident ray is precisely at the critical angle, the refracted ray is tangent to the boundary at the point of incidence. If for example, visible light were traveling from a glass (i.e. Lucite with an index of refraction of 1.50) into air (with an index of refraction of 1.00). The calculation would give a result of: For other uses, see tangent (disambiguation). ...

$theta_c = arcsin left( frac{n_2}{n_1} right),$

when $n 2$ = index of refraction of air (1.00) and $n 1$ = index of refraction of Lucite (1.50),

$theta_c = arcsin left( frac {1.00}{1.50} right) = 41.8,$

This calculation gives the critical angle for light from Lucite into air. Keep in mind that if the angle of the light were at the critical angle then the refracted beam would be on the border of the glass-air border.

The critical angle for diamond is about 24.4°, which means that light is much more likely to be internally reflected within a diamond. Diamonds for jewelry are cut to take advantage of this; in particular the brilliant cut is designed to achieve high total reflection of light entering the diamond, and high dispersion of the reflected light (known to jewelers as fire). This article is about the mineral. ... In order to best utilize a diamond gemstones superlative material properties, a number of different diamond cuts have been developed. ... A scattering of brilliant cut diamonds shows off the many reflecting facets. ... Dispersion of a light beam in a prism. ...

If the fraction: $frac{n_2}{n_1}$ is greater than 1, then arcsine is not defined--meaning that total internal reflection does not occur even at very shallow or grazing incident angles. So the critical angle is only defined for $frac{n_2}{n_1}leq1$ .

Frustrated total internal reflection

Under "ordinary conditions" it is true that the creation of an evanescent wave does not affect the conservation of energy, i.e. the evanescent wave transmits zero net energy. However, if a third medium with a higher refractive index than the second medium is placed within less than several wavelengths distance from the interface between the first medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and it will pass energy across the second into the third medium. (See evanescent wave coupling.) An evanescent wave is an electromagnetic wave that decays exponentially with distance. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Evanescent Wave Coupling is a process by which electromagnetic waves are transmitted from one medium to another by means of the evanescent (or decaying) electromagnetic field(s). ...

A transparent, low refractive index material is sandwiched between two prisms of another material. This allows the beam to "tunnel" through from one prism to the next in a process very similar to quantum tunneling while at the same time altering the direction of the incoming ray. Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...

Applications

Optical fibers, which are used in endoscopes and telecommunications.
Rain sensors to control automatic windscreen/windshield wipers.
Another interesting application of total internal reflection is the spatial filtering of light.[1]
Multi-touch screens [2] use frustrated total internal reflection in combination with a camera and appropriate software to pick up multiple targets.
Gonioscopy to view the anatomical angle formed between the eye's cornea and iris.

Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... Endoscopy means looking inside and refers to looking inside the human body for medical reasons. ... Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... A rain sensor is a water conservation device connected to an automatic irrigation system that causes the system to shut down in the event of rainfall. ... windscreen wiper on a parked car. ... Multi-touch is a human-computer interaction technique and the hardware devices that implement it. ... Gonioscopy describes the use of a goniolens (also known as a gonioscope) in conjunction with a slit lamp or operating microscope to gain a view of the iridocorneal angle, or the anatomical angle formed between the eyes cornea and iris. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ...

Simple household example

To easily demonstrate total internal reflection, fill a sink or bath with water, take a glass tumbler, and place it in the water so that it fills completely with water. place the tumbler upturned over the plug hole. While water remains both in the upturned tumbler and in the sink surrounding the tumbler, the plug hole and plug is visible since the angle of refraction between glass and water is not greater than the critical angle. Now pull the plug, but keeping the tumbler in position over the plug hole. The water in the tumbler will empty into the plug hole, leaving the glass filled with air, and acting as the plug. Viewing this from above, the tumbler now appears mirrored because light reflects off of the air/glass interface.

References

Federal Standard 1037C and MIL-STD-188

Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ... MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...

External links

FTIR Touch Sensing
Multi-Touch Interaction Research
iBar Intelligent Surface System
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html

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Results from FactBites:

Total Internal Reflection (1431 words)
	That is, as the angle of incidence is increased, the brightness of the refracted ray decreases and the brightness of the reflected ray increases.
	Total internal reflection (TIR) is the phenomenon which involves the reflection of all the incident light off the boundary.
	Total internal reflection will not take place unless the incident light is traveling within the more optically dense medium towards the less optically dense medium.

Nikon MicroscopyU: Fluorescence Microscopy - Total Internal Reflection Fluorescence (4510 words)
	Total internal reflection is only possible in situations in which the propagating light encounters a boundary to a medium of lower refractive index.
	The basic concept of total internal reflection fluorescence is schematically illustrated in Figure 1, in which specimen cells incorporating fluorescent molecules (green fluorophores in the figure) are supported on a glass microscope slide.
	Total internal reflection does not occur suddenly as a new phenomenon at the critical angle, but a continuous transition is followed from predominant refraction with a small amount of reflection, to total reflection when the critical angle is exceeded.

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