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Photonics Dictionary: E

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exposure index
A measure of film speed sensitivity to light.
exposure meter
An instrument used to measure the light from a scene to be photographed and to indicate the camera lens and shutter settings required to expose the film correctly. The exposure time required in a...
exposure time
The length of time during which the receiver is irradiated.
ext
external
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 fiber loss
A type of optical fiber loss resulting from the misalignment of fibers in a splice or connector.
extrinsic joint loss
Synonym of extrinsic fiber loss.
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 box
The area in a 2-D or 3-D microdisplay viewer within which the eye can move and still see the entire image.
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 guard
A shield of rubber, plastic or metal used to protect the eyes of the observer from stray light and wind, and to maintain the proper eye distance.
eye lens
The lens of an eyepiece nearest the observer's eye.
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 shield -> eye guard
A shield of rubber, plastic or metal used to protect the eyes of the observer from stray light and wind, and to maintain the proper eye distance.
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 tracker
An optical device used to monitor movement of the human eye.
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
Also known as ocular. The lens system used between the final real image in a visual optical system and eye. It acts as an image magnifier. Many types of eyepieces are known; e.g., the Huygens used in...
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...

Photonics DictionaryE

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