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8,726 terms

Photonics Dictionary

ETIR

environmental thermal infrared

ETOM

electron trapping optical memory

eutectic

The material that has the lowest possible constant melting point of any possible combination of the same components.

EUV

extreme ultraviolet

electron volt

evanescent field theory

A high-frequency approach to the propagation of light in graded-index fibers in which the modal field is represented in terms of an inhomogeneous (evanescent) plane wave with a complex phase, so that...

evaporagraph

A sensor generally used for infrared imaging. It consists of two chambers separated by a thin, blackened membrane. An infrared image is formed on the membrane by a lens or mirror and produces...

evaporation coating

Coating carried out in a sealed chamber evacuated by a mechanical pump in series with an oil diffusion pump to a pressure less than 10-4 mm of mercury, measured by a vacuum gauge. At such a low...

evapotranspiration

A process, either naturally occurring or mechanically induced, whereby water is changed from its liquid state into a vapor.

event-based sensor

An event-based image sensor, also known as a dynamic vision sensor (DVS), is a type of digital imaging device designed to capture visual information in a highly efficient and unique way compared to...

EVR

electronic video recording

electronic warfare; early warning

EWACS

electronic wide-angle camera system

exa

In the SI system, prefix meaning 1018. (E).

EXAFS

extended x-ray absorption edge fine structure

excess noise factor

A factor, F, indicating the increase in shot noise in an avalanche photodiode as compared with the ideal multiplier, which is noiseless. The noise, which results from variations in avalanche gains,...

excimer

A contraction of "excited dimer." The term refers to an excited species made by combination of two identical atoms or molecules, one of which is excited and one of which is at a ground...

excimer laser

An excimer laser is a type of ultraviolet laser that emits short pulses of light in the ultraviolet spectrum. The term excimer is derived from excited dimer, reflecting the nature of the gain medium...

excimer laser coronary angioplasty

Excimer laser coronary angioplasty (ELCA) refers to a medical procedure used in the treatment of coronary artery disease. This technique involves the use of an excimer laser to perform angioplasty, a...

exciplex

The term "excimer," strictly used, refers to excited species made by combination of two identical moieties, atoms or molecules. Excited complexes that do not fall into this category are...

excitation

1. The process by which an atom acquires energy sufficient to raise it to a quantum state higher than its ground state. 2. More specifically with respect to lasers, the process by which the material...

excitation energy

The difference between the energy of an atom in its ground state and that of the same atom in its excited (quantum) state.

excitation index

The ratio of the intensities of two specified spectral lines of a source having vastly different excitation energies. This ratio indicates the level of excitation energy in the source.

excitation potential

The amount of energy required to raise the energy level of an atom; a necessity if the atom is to radiate energy. High excitation potential is the amount of energy in the upper state of the...

excitation purity

On the CIE chromaticity diagram, the distance from the achromatic point to the sample point, divided by the distance from the achromatic point through the sample point to the spectrum locus or purple...

excitation volume

The amount of x-rays used to penetrate and diffuse a target sample undergoing electron-probe microanalysis.

excited state

The stationary state of an ion, atom or molecule, above the ground state that is produced by the interaction with the radiation field or another ion, atom or molecule. See ground state.

excited-state absorption

In laser pumping, parasitic absorption that occurs at certain wavelengths, decreasing pump efficiency and gain.

exciter filter

In ultraviolet and fluorescence photography, the term applied to the filter used in the photographic system and with the exciting source to screen out ambient radiations and to transmit the exciting...

exciter lamp

A small incandescent lamp whose intense beam is focused on the optical soundtrack of a motion picture film. The soundtrack modulates the beam, which in turn is detected by a photocell that produces...

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...

excitron

A single-anode mercury pool tube that is designed to maintain a continuous cathode spot.

exit angle

The angle between a light ray emerging from an optical system and the optical axis of that system.

exit pupil

In a lens or other optical system, the image of the aperture stop as seen from image space.

exitance

Flux leaving a surface per unit area.

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.

explosive variable

In cosmology, a star that exhibits a rapid increase in the magnitude of light, which is followed by a slow decrease in magnitude. The nova and supernova are explosive variables.

exposure

In optics, the total radiant energy incident on a surface-per-unit area. It is equal to the integral over time of the radiant flux density. Also known as radiant exposure.

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.

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