|
|
| Line 1: |
Line 1: |
| {{Two other uses|a prism in optics|a prism in geometry|Prism (geometry)}}
| | [http://www.Answers.com/topic/Roberto Roberto] is the name I love to be called with though I generally really like being categorised as like that. South Carolina is where all of my home is and Since i don't plan on enhancing it. To drive is a thing that I'm ultimately addicted to. Managing those has been my times job for a even while but I plan to changing it. I'm not good at web development but you might need to check my website: http://prometeu.net<br><br> |
| {{Redirect|Prismatic||Prismatic (disambiguation)}}
| |
| [[File:Prism-side-fs PNr°0117.jpg|thumb|upright|right|A plastic prism]]
| |
| In [[optics]], a '''prism''' is a transparent optical element with flat, polished surfaces that [[refraction|refract]] [[light]]. At least two of the flat surfaces must have an angle between them. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a [[triangular prism]] with a triangular base and rectangular sides, and in colloquial use "prism" usually refers to this type. Some types of optical prism are not in fact in the shape of [[prism (geometry)|geometric prisms]]. Prisms can be made from any material that is transparent to the [[wavelength]]s for which they are designed. Typical materials include [[glass]], [[plastic]] and [[Fluorite#Optics|fluorite]].
| |
|
| |
|
| A [[dispersive prism]] can be used to break light up into its constituent [[spectrum|spectral]] [[color]]s (the colors of the [[rainbow]]). Furthermore, prisms can be used to [[reflection (physics)|reflect]] light, or to split light into components with different [[polarization (waves)|polarization]]s.
| | My blog: clash of clans cheats ([http://prometeu.net go to this site]) |
| | |
| == How prisms work ==
| |
| [[Image:Light dispersion conceptual waves.gif|thumb|330px|A triangular prism, dispersing light; waves shown to illustrate the differing wavelengths of light. (Click to view animation)]]
| |
| Light changes [[speed]] as it moves from one medium to another (for example, from air into the glass of the prism). This speed change causes the light to be [[refracted]] and to enter the new medium at a different angle ([[Huygens principle]]). The degree of bending of the light's path depends on the angle that the [[incident ray|incident]] beam of light makes with the surface, and on the ratio between the [[refractive index|refractive indices]] of the two media ([[Snell's law]]). The refractive index of many materials (such as glass) varies with the [[wavelength]] or color of the light used, a phenomenon known as ''[[dispersion (optics)|dispersion]]''. This causes light of different colors to be refracted differently and to leave the prism at different angles, creating an effect similar to a [[rainbow]]. This can be used to separate a beam of white light into its constituent [[spectrum]] of colors. Prisms will generally disperse light over a much larger frequency bandwidth than [[diffraction grating]]s, making them useful for broad-spectrum [[spectroscopy]]. Furthermore, prisms do not suffer from complications arising from overlapping spectral orders, which all gratings have.
| |
| | |
| Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion. If light inside the prism hits one of the surfaces at a sufficiently steep angle, [[total internal reflection]] occurs and ''all'' of the light is reflected. This makes a prism a useful substitute for a [[mirror]] in some situations.
| |
| | |
| ===Deviation angle and dispersion===
| |
| | |
| [[Image:prism ray trace.svg|thumb|right|400px|A ray trace through a prism with apex angle α. Regions 0, 1, and 2 have [[Refractive index|indices of refraction]] <math>n_0</math>, <math>n_1</math>, and <math>n_2</math>, and primed angles <math>\theta'</math> indicate the ray angles after refraction.]]
| |
| [[Ray (optics)|Ray]] angle deviation and dispersion through a prism can be determined by [[Ray tracing (physics)|tracing]] a sample ray through the element and using [[Snell's law]] at each interface. For the prism shown at right, the indicated angles are given by
| |
| :<math>\begin{align}
| |
| \theta'_0 &= \, \text{arcsin} \Big( \frac{n_0}{n_1} \, \sin \theta_0 \Big) \\
| |
| \theta_1 &= \alpha - \theta'_0 \\
| |
| \theta'_1 &= \, \text{arcsin} \Big( \frac{n_1}{n_2} \, \sin \theta_1 \Big) \\
| |
| \theta_2 &= \theta'_1 - \alpha
| |
| \end{align}</math>.
| |
| For a prism in air <math>n_0=n_2 \simeq 1</math>. Defining <math>n=n_1</math>, the deviation angle <math>\delta</math> is given by
| |
| :<math>\delta = \theta_0 + \theta_2 = \theta_0 + \text{arcsin} \Big( n \, \sin \Big[\alpha - \text{arcsin} \Big( \frac{1}{n} \, \sin \theta_0 \Big) \Big] \Big) - \alpha</math> | |
| If the angle of incidence <math>\theta_0</math> and prism apex angle <math>\alpha</math> are both small, <math>\sin \theta \approx \theta</math> and <math>\text{arcsin} x \approx x</math> if the angles are expressed in [[radian]]s. This allows the [[nonlinear equation]] in the deviation angle <math>\delta</math> to be approximated by
| |
| :<math>\delta \approx \theta_0 - \alpha + \Big( n \, \Big[ \Big(\alpha - \frac{1}{n} \, \theta_0 \Big) \Big] \Big) = \theta_0 - \alpha + n \alpha - \theta_0 = (n - 1) \alpha \ .</math>
| |
| | |
| The deviation angle depends on wavelength through ''n'', so for a thin prism the deviation angle varies with wavelength according to
| |
| :<math>\delta (\lambda) \approx [ n (\lambda) - 1 ] \alpha </math>.
| |
| | |
| == Prisms and the nature of light ==
| |
| [[File:Light dispersion of a mercury-vapor lamp with a flint glass prism IPNr°0125.jpg|thumb|upright|right|A triangular prism, dispersing light]]
| |
| Before [[Isaac Newton]], it was believed that white light was colorless, and that the prism itself produced the color. Newton's experiments demonstrated that all the colors already existed in the light in a heterogeneous fashion, and that "corpuscles" (particles) of light were fanned out because particles with different colors traveled with different speeds through the prism. It was only later that [[Thomas Young (scientist)|Young]] and [[Augustin-Jean Fresnel|Fresnel]] combined Newton's particle theory with Huygens' wave theory to show that color is the visible manifestation of light's wavelength.
| |
| | |
| Newton arrived at his conclusion by passing the red color from one prism through a second prism and found the color unchanged. From this, he concluded that the colors must already be present in the incoming light — thus, the prism did not create colors, but merely separated colors that are already there. He also used a lens and a second prism to recompose the spectrum back into white light. This experiment has become a classic example of the methodology introduced during the [[scientific revolution]]. The results of this experiment dramatically transformed the field of [[metaphysics]], leading to [[John Locke]]'s [[Primary/secondary quality distinction|primary vs secondary quality distinction]].
| |
| | |
| Newton discussed prism dispersion in great detail in his book ''[[Opticks]]''.<ref>{{cite book| author=I. Newton| title = [[Opticks]]| publisher=Royal Society|location=London| year=1704| isbn=0-486-60205-2}}</ref> He also introduced the use of more than one prism to control dispersion.<ref>{{cite web|url=http://www.juliantrubin.com/bigten/lightexperiments.html|title=The Discovery of the Spectrum of Light|accessdate=19 December 2009}}</ref> Newton's description of his experiments on prism dispersion was qualitative, and is quite readable. A quantitative description of [[Multiple-prism dispersion theory|multiple-prism dispersion]] was not needed until multiple prism laser [[beam expander]]s were introduced in the 1980s.<ref>{{cite journal | doi=10.1016/0030-4018(82)90216-4 | author=[[F. J. Duarte]] and J. A. Piper | title=Dispersion theory of multiple-prism beam expanders for pulsed dye lasers| journal=Opt. Commun.|volume=43|pages=303–307 |year=1982|bibcode = 1982OptCo..43..303D }}</ref>
| |
| | |
| ==Types of prisms==
| |
| | |
| ===Dispersive prisms===
| |
| [[File:comparison refraction diffraction spectra.svg|thumb|upright|Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet).]]
| |
| {{Main|Dispersive prism}}
| |
| ''Dispersive prisms'' are used to break up light into its constituent spectral colors because the refractive index depends on [[frequency]]; the white light entering the prism is a mixture of different frequencies, each of which gets bent slightly differently. Blue light is slowed down more than red light and will therefore be bent more than red light.
| |
| | |
| *[[Triangular prism (optics)|Triangular prism]]
| |
| *[[Abbe prism]]
| |
| *[[Pellin–Broca prism]]
| |
| *[[Amici prism]]
| |
| *[[Compound prism]]
| |
| *[[Grism]], a dispersive prism with a diffraction grating on its surface
| |
| | |
| ===Reflective prisms===
| |
| ''Reflective prisms'' are used to reflect light, in order to flip, invert, rotate, deviate or displace the light beam. They are typically used to erect the image in [[binoculars]] or [[single-lens reflex camera]]s – without the prisms the image would be upside down for the user. Many reflective prisms use [[total internal reflection]] to achieve high reflectivity.
| |
| | |
| The most common reflective prisms are:
| |
| *[[Porro prism]]
| |
| *[[Porro–Abbe prism]]
| |
| *[[Amici roof prism]]
| |
| *[[Pentaprism]] and roof pentaprism
| |
| *[[Abbe–Koenig prism]]
| |
| *[[Schmidt–Pechan prism]]
| |
| *[[Bauernfeind prism]]
| |
| *[[Dove prism]]
| |
| *[[Retroreflector]] prism
| |
| | |
| ====Beam-splitting prisms====
| |
| Some reflective prisms are used for splitting a beam into two or more beams:
| |
| *[[Beam splitter|Beam splitter cube]]
| |
| *[[Dichroic prism]]
| |
| | |
| ===Polarizing prisms===
| |
| | |
| There are also ''polarizing prisms'' which can split a beam of light into components of varying [[polarization (waves)|polarization]]. These are typically made of a [[birefringent]] crystalline material.
| |
| *[[Nicol prism]]
| |
| *[[Wollaston prism]]
| |
| *[[Nomarski prism]] – a variant of the Wollaston prism with advantages in microscopy
| |
| *[[Rochon prism]]
| |
| *[[Sénarmont prism]]
| |
| *[[Glan–Foucault prism]]
| |
| *[[Glan–Taylor prism]]
| |
| *[[Glan–Thompson prism]]
| |
| | |
| ===Deflecting prisms===
| |
| [[Wedge prism]]s are used to deflect a beam of light by a fixed angle. A pair of such prisms can be used for [[beam steering]]; by rotating the prisms the beam can be deflected into any desired angle within a conical "field of regard". The most commonly found implementation is a [[Risley prism]] pair.<ref>{{cite journal| doi=10.1117/1.1556393| author=B.D. Duncan et al.| title=Wide-angle achromatic prism beam steering for infrared countermeasure applications|journal=Opt. Eng.|volume=42|pages=1038–1047 | year=2003|bibcode = 2003OptEn..42.1038D }}</ref> Two wedge prisms can also be used as an ''anamorphic pair'' to change the shape of a beam. This is used to make a round beam from the elliptical output of a [[laser diode]].<ref>http://www.edmundoptics.com/optics/prisms/specialty-prisms/wedge-prisms/2052</ref>
| |
| | |
| Rhomboid prisms are used to laterally displace a beam of light without inverting the image.<ref>http://www.edmundoptics.com/optics/prisms/specialty-prisms/rhomboid-prisms/2431</ref>
| |
| | |
| [[Deck prism]]s were used on sailing ships to bring daylight below deck, since candles and [[kerosene lamp]]s are a fire hazard on wooden ships.
| |
| | |
| ==In optometry==
| |
| By shifting [[corrective lens]]es off [[optical axis|axis]], images seen through them can be displaced in the same way that a prism displaces images. [[Eye care professional]]s use prisms, as well as lenses off axis, to treat various [[orthoptics]] problems:
| |
| | |
| *[[Diplopia]]
| |
| *Positive and negative fusion problems{{Ambiguous|date=July 2011}}
| |
| *[[Positive relative accommodation]] and [[negative relative accommodation]] problems
| |
| | |
| ==See also==
| |
| {{Commons category|Prisms}}
| |
| *[[Minimum deviation]]
| |
| *[[Multiple-prism dispersion theory]]
| |
| *[[Prism compressor]]
| |
| *[[Prism dioptre]]
| |
| *[[Prism (geometry)]]
| |
| *[[Theory of Colours]]
| |
| *[[Triangular prism]] (geometry)
| |
| *[[Superprism]]
| |
| *[[Eyeglass prescription]]
| |
| | |
| ==References==
| |
| {{reflist}}
| |
| | |
| ==Further reading==
| |
| * {{cite book | author=Hecht, Eugene | title=Optics | edition=4th | publisher=Pearson Education | year=2001 | isbn=0-8053-8566-5}}
| |
| {{Use dmy dates|date=July 2011}}
| |
| | |
| ==External links==
| |
| * [http://www.phy.hk/wiki/englishhtm/RefractionByPrism.htm Java applet of refraction through a prism]
| |
| * [http://gratings.newport.com/information/handbook/chapter12.asp#12.3/ Grisms (Grating Prisms)]
| |
| * [http://www.cvimellesgriot.com/Products/Documents/TechnicalGuide/Fundamental-Optics.pdf Fundamental Optics] – CVI Melles Griot
| |
| | |
| [[Category:Optical devices]]
| |
| [[Category:Prisms| ]]
| |
Roberto is the name I love to be called with though I generally really like being categorised as like that. South Carolina is where all of my home is and Since i don't plan on enhancing it. To drive is a thing that I'm ultimately addicted to. Managing those has been my times job for a even while but I plan to changing it. I'm not good at web development but you might need to check my website: http://prometeu.net
My blog: clash of clans cheats (go to this site)