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An Amici prism, named for the astronomer
An Amici prism, named for the astronomer Giovanni Battista Amici
Giovanni Battista Amici (; 25 March 1786 – 10 April 1863) was an Italian astronomer, microscopist, and botanist.
Amici was born in Modena, in present-day Italy. After studying at Bologna, he became professor of mathematics at Modena, and in 1 ...
, is a type of compound dispersive prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
used in spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where th ...
s. The Amici prism consists of two triangular prism
In geometry, a triangular prism is a three-sided prism; it is a polyhedron made of a triangular base, a translated copy, and 3 faces joining corresponding sides. A right triangular prism has rectangular sides, otherwise it is ''oblique''. ...
s in contact, with the first typically being made from a medium-dispersion crown glass, and the second a higher-dispersion flint glass
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refracti ...
. Light entering the first prism is refracted at the first air-glass interface, refracted again at the interface between the two prisms, and then exits the second prism at near-normal incidence. The prism angles and materials are chosen such that one wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
(colour
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
) of light, the ''centre wavelength'', exits the prism parallel to (but offset from) the entrance beam. The prism assembly is thus a ''direct-vision prism'', and is commonly used as such in hand-held spectroscope
An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mat ...
s. Other wavelengths are deflected at angles depending on the glass dispersion
Dispersion may refer to:
Economics and finance
* Dispersion (finance), a measure for the statistical distribution of portfolio returns
*Price dispersion, a variation in prices across sellers of the same item
* Wage dispersion, the amount of variat ...
of the materials. Looking at a light source through the prism thus shows the optical spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to wa ...
of the source.
By 1860, Amici realized that one can join this type of prism back-to-back with a reflected copy of itself, producing a three-prism arrangement known as a double Amici prism. This doubling of the original prism increases the angular dispersion of the assembly, and also has the useful property that the centre wavelength is refracted back into the direct line of the entrance beam. The exiting ray of the center wavelength is thus not only undeviated from the incident ray, but also experiences no translation (i.e. transverse displacement or offset) away from the incident ray's path.
Amici himself never published about his nondeviating prism, but rather communicated the idea to his friend Donati, who constructed the device for observations of stellar spectra. Donati's publications of his observations (in 1862) were the first disclosure of the prism doubling idea, and because the prism was practical to build and much more compact than multiple prism arrangements typical of that period for producing high spectral dispersion, Amici's invention quickly caught the attention of researchers throughout Europe. The dispersion of Amici prisms can be accurately calculated using the multiple-prism dispersion theory assuming no spatial separation between the prism components.F. J. Duarte
Francisco Javier "Frank" Duarte (born c. 1954) is a laser physicist and author/editor of several books on tunable lasers.
His research on physical optics and laser development has won several awards, including an Engineering Excellence Award in ...
, Tunable laser optics: applications to optics and quantum optics, ''Progress in Quantum Electronics'' 37, 326-347 (2013).
The dispersive Amici prism should not be confused with the non-dispersive Amici roof prism
An Amici roof prism, named for its inventor, the Italian astronomer Giovanni Battista Amici, is a type of reflecting prism used to deviate a beam of light by 90° while simultaneously inverting the image. It is commonly used in the eyepieces of ...
.
References
{{Reflist Prisms (optics) Italian inventions