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For other uses, see Prism (disambiguation).
If a shaft of light entering a prism is sufficiently narrow, a spectrum results.
If a shaft of light entering a prism is sufficiently narrow, a spectrum results.

In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. Refraction is the change in direction of a Wave due to a change in its Speed. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 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. In Geometry, a triangular prism or three-sided prism is a type of prism; it is a Polyhedron made of a triangular base a translated Some types of optical prism are not in fact in the shape of geometric prisms. General right and uniform prisms A right prism is a prism in which the joining edges and faces are perpendicular to the base faces Prisms are typically made out of glass, but can be made from any material that is transparent to the wavelengths for which they are designed. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency.

A prism can be used to break light up into its constituent spectral colors (the colors of the rainbow). A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun Prisms can also be used to reflect light, or to split light into components with different polarizations. Reflection is the change in direction of a Wave front at an interface between two different media so that the wave front returns into the medium from which Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations

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How prisms work

A triangular prism, dispersing light
A triangular prism, dispersing light

Light changes speed as it moves from one medium to another (for example, from air into the glass of the prism). Speed is the rate of motion, or equivalently the rate of change in position often expressed as Distance d traveled per unit of This speed change causes the light to be refracted and to enter the new medium at a different angle (Huygens principle). Refraction is the change in direction of a Wave due to a change in its Speed. The Huygens–Fresnel principle (named for Dutch Physicist Christiaan Huygens, and French physicist Augustin-Jean Fresnel The degree of bending of the light's path depends on the angle that the incident beam of light makes with the surface, and on the ratio between the refractive indices of the two media (Snell's law). 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 In Optics and Physics, Snell's law (also known as Descartes' law or the law of refraction) is a formula used to describe the relationship The refractive index of many materials (such as glass) varies with the wavelength or color of the light used, a phenomenon known as dispersion. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency 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. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun This effect can be used to separate a beam of white light into its constituent spectrum of colors. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. Prisms will generally disperse light over a much larger frequency bandwidth than diffraction gratings, making them useful for broad-spectrum spectroscopy. In Optics, a Diffraction grating is an optical component with a regular pattern which splits ( diffracts) light into several beams travelling in different Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ 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. A mirror is an object with a surface that has good Specular reflection; that is it is smooth enough to form an Image.

Prisms and the nature of light

In Isaac Newton's time, it was believed that white light was colorless, and that the prism itself produced the color. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Newton's experiments convinced him 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 Young and Fresnel combined Newton's particle theory with Huygen's wave theory to show that color is the visible manifestation of light's wavelength. Thomas Young (13 June 1773 &ndash 10 May 1829 was an English Polymath who contributed to the scientific understanding of vision, Light

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 period which many historians of science call the Scientific Revolution can be roughly dated as having begun in 1543 the year in which Nicolaus Copernicus published The results of this experiment dramatically transformed the field of metaphysics, leading to John Locke's primary vs secondary quality distinction. Metaphysics is the branch of Philosophy investigating principles of reality transcending those of any particular science John Locke (29 August 1632 – 28 October 1704 was an English Philosopher. The primary/secondary quality distinction is a conceptual distinction in Epistemology and Metaphysics, concerning the nature of Reality.

Newton discussed prism dispersion in great detail in his book Opticks. Opticks is a book written by English physicist Isaac Newton that was released to the public in 1704. [1] He also introduced the use of more than one prism to control dispersion. Newton's description of his experiments on prism dispersion was qualitative, and is quite readable. A quantitative description of multiple-prism dispersion was not needed until multiple prism laser beam expanders were introduced in the 1980's. [2]

Types of prisms

Dispersive prisms

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. Frequency is a measure of the number of occurrences of a repeating event per unit Time. Blue light is slowed down more than red light and will therefore be bent more than red light.

Reflective prisms

Reflective prisms are used to reflect light, for instance in binoculars. In Optics, a dispersive prism is a type of optical prism, normally having the shape of a geometrical triangular prism. In Optics, an Abbe prism, named for its inventor the German physicist Ernst Abbe, is a type of constant deviation dispersive prism A Pellin-Broca prism is a type of constant deviation dispersive prism similar to an Abbe prism. An Amici prism, named for the astronomer Giovanni Amici, is a type of compound dispersive prism which is used as a Spectrometer. Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and

Polarizing prisms

There are also polarizing prisms which can split a beam of light into components of varying polarization. A pentaprism is a five-sided reflecting prism used to deviate a beam of Light by 90° In Optics, a Porro prism, named for its inventor Ignazio Porro, is a type of reflection prism used in optical instruments to alter the orientation A Porro-Abbe prism (sometimes called a Abbe-Porro prism) named for Ignazio Porro and Ernst Abbe, is a type of reflection prism used in some An Abbe-Koenig prism is a type of reflecting prism used to invert an image (rotate it by 180° A Schmidt-Pechan prism is a type of optical prism used to rotate an image by 180°. A Dove prism is a type of reflective prism which is used to invert an Image. A dichroic prism is a prism that splits Light into two beams of differing Wavelength ( Colour) An Amici roof prism, named for its inventor the Italian Astronomer Giovanni Amici, is a type of reflecting prism used to deviate a beam of light by Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations These are typically made of a birefringent crystalline material. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray

See also

References

  1. ^ I. Newton, Opticks (Royal Society, London, 1704). Opticks is a book written by English physicist Isaac Newton that was released to the public in 1704.
  2. ^ F. J. Duarte and J. A. Piper, Opt. Commun. 43, 303–307 (1982).

External links

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