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5,268 terms
Photonics Dictionary
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exciton
An exciton is a quasiparticle that represents the bound state of an electron and a hole in a solid-state material, typically a semiconductor or an insulator. In simpler terms, an exciton is a paired...
exp
exponential function of
explosion spectrum
The light spectrum formed by an explosive reaction or by the electrical explosion of a metallic wire by a strong current.
extended source
A radiation source that, unlike the point source, can be resolved by the naked eye into a geometrical image.
extensometer
1. A strainmeter capable of measuring the change in the relationship between two reference points, provided that the points are separated by at least 20 to 30 m. 2. An instrument used to determine...
external photoelectric effect
The ejection of electrons from the surface of a solid by the absorption of a sufficient amount of photons.
extinction
1. The near total absorption of plane-polarized light by a polarizer that has an axis perpendicular to the plane of polarization. 2. The decrease in the intensity of a diffracted beam resulting from...
extinction meter
A type of exposure meter that artificially reduces the light admitted in a sequence of known fractions until a value is reached that is equivalent to the proper exposure.
extinction ratio
The ratio of the power of a plane-polarized beam that is transmitted through a polarizer placed in its path with its polarizing axis parallel to the beam's plane, as compared with the transmitted...
extinction voltage
The lowest anode voltage at which a gas tube can sustain a discharge.
extramural absorption cement
A cement used to reduce crosstalk in fiber optic bundles or plates.
extraordinary ray
A ray that has a nonisotropic speed in a doubly refracting crystal. It does not necessarily obey Snell's law upon refraction at the crystal surface.
extraterrestrial radiation
Radiation that is emitted by a source outside the Earth and its atmosphere.
extreme ultraviolet
Extreme ultraviolet (EUV) refers to a specific range of electromagnetic radiation in the ultraviolet part of the spectrum. EUV radiation has wavelengths between 10 and 124 nanometers, which...
extrinsic detector
A photodetector composed of a semiconductor material whose responsive properties can be altered by the addition of impurities to the basic material. Copper- and mercury-doped germanium are both...
extrinsic photoconductivity
Photoconductivity due to the addition of impurities or external causes.
extrinsic properties
The properties exhibited by a semiconductor as the result of its modification by imperfections and impurities in the crystal.
eye
The organ of vision or light sensitivity.
eye distance
->
eye relief
Also termed eye distance. The distance between the vertex of the last optical surface of a visual optical system and the system's exit pupil.
eye pattern
A pattern on an oscilloscope display that consists of a string of shapes that resemble eyes. Because the pattern becomes more closed with increasing distortion and interference, an open eye diagram...
eye relief
Also termed eye distance. The distance between the vertex of the last optical surface of a visual optical system and the system's exit pupil.
eye test apparatus
Instruments used by ophthalmologists and optometrists to study the eye. There are, for instance, the ophthalmoscope to observe and photograph the retina; the retinoscope and optometer to determine...
eye-safe laser operation
Wavelengths between 400 and 1400 nm (VIS to NIR) are focused onto the retina by the cornea. Because the retina is sensitive to light, these wavelengths can be damaging even at low energies. It is the...
eyepiece micrometer
->
measuring eyepiece
Also known as an eyepiece micrometer. A microscope eyepiece that has a finely divided scale ruled or photographed on a section of transparent glass, and located in the focal plane. The dimensions of...
f
number (
f
/#)
The expression denoting the ratio of the equivalent focal length of a lens to the diameter of its entrance pupil.
f-Theta lens
An f-theta lens, also known as an f-theta scan lens or simply an f-theta lens system, is a specialized optical component used in laser scanning systems, particularly in laser marking, engraving, and...
F-center
->
color center
A color center, in the context of materials science and condensed matter physics, refers to a specific type of crystallographic defect in a crystalline structure that introduces color to the...
Fabry-Perot interferometer
A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth...
Fabry-Perot laser
A laser oscillator in which two mirrors are separated by an amplifying medium with an inverted population, making a Fabry-Perot cavity. Standard diode lasers are Fabry-Perot lasers.
Fabry-Perot method
A means of determining a prism's index of refraction by placing the prism so that its emergent face is perpendicular to the incident beam. This arrangement permits the determination of the prism's...
Fabry-Perot mirror
A highly reflective mirror that is usually flat on one surface and curved on the other, and that has silver, gold or aluminum deposited on glass, providing about 99 percent reflection.
face-pumped laser
A device in which slab geometry internally compensates for thermal-optic distortion; the solid host material -- glass or Nd:YAG -- is in the form of a rectangular slab with plane parallel faces. The...
facet
1. One of the plane-reflecting surfaces on a multisurfaced polygon. 2. The cleaved end mirror of a laser diode's active region.
facet erosion
The degradation of the facets in a laser diode due to the intensity of radiation.
facsimile radio
The conversion of a still picture into sound waves and its subsequent transmission by radio.
facsimile synchronizing
The maintenance of the same scanning relationship between the transmitting scanning spot and receiving scanning spot for each scanning line transmitted in a facsimile system.
facsimile
The reproduction of a picture or image, produced by scanning the image and converting it into electrical signals that carry the image to be reproduced. Also known as fax.
false color
In imaging technology, assigning color to black and white images to differentiate features or convey information. Also called colorizing.
fan
A set of rays through a lens originating at a common point and contained in one plane.
fan-in
The simultaneous collection of two or more signals at a single location. In a digital computer, it refers to the number of inputs that can be accommodated by a particular logic circuit.
fan-out
The distribution of one signal to more than one location. In a digital computer, it refers to the number of outputs that can be fed by a particular logic circuit.
FAR
Federal Acquisition Regulation; false alarm rate
far point (of vision)
The object distance at which the eye is focused with the eye lens in a neutral or relaxed state.
far-field diffraction pattern
The diffraction pattern of a source such as a light-emitting diode, injection laser diode or the output end of an optical waveguide observed at an infinite distance from the source.
far-field region
A region far from an aperture or source where the diffraction pattern is essentially the same as that at infinity. Changes in diffraction patterns of points within the far-field region are...
far-infrared grating
A grating with very coarse rulings to match the long wavelengths in the far-infrared region. In the most efficient ruling method, grooves are cut in plane, solid aluminum alloy blanks.
far-infrared laser
A laser with output over a wide range of wavelengths spanning the far-infrared region of the spectrum (30 to 1000 µm); typically, it consists of a metal or dielectric waveguide one to two...
far-infrared maser
A gas maser that is capable of producing radiation in the far-infrared region of the spectrum.
far-ultraviolet radiation
That radiation characterized by wavelengths ranging from 0.2 to 0.3 µm in the electromagnetic spectrum.
Faraday configuration
Describes incident radiation propagating parallel to an externally applied magnetic field in magneto-optical experimentation.
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Photonics Dictionary
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