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Photonics Dictionary: E

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ESR
electrical substitution radiometer; electron spin resonance
ESSA
environmental survey satellite
ESTM
electron scanning tunneling microscope
esu
electrostatic unit
ET
ephemeris time
etalon
An etalon is an optical device that consists of two parallel reflecting surfaces separated by a precise and known distance. It operates based on the principle of optical interference and is used to...
etaloning
Etaloning is an optical phenomenon that occurs in imaging systems, particularly in devices such as spectrometers, interferometers, and cameras. It is characterized by the appearance of interference...
etching
The engraving of a surface by acid, acid fumes or a tool; a process extensively used in the manufacture of reticles.
etching liquid
An acid used to etch the surfaces of particular materials. For glass, hydrofluoric acid is used either as a liquid or a vapor. Metals are etched by means of suitable acids or other liquids, often to...
ETD
edge thickness difference
etendue
A product of the area of a light beam (normal to its direction of propagation) and the solid angle that the beam includes; flux per unit radiance or luminance. Alternative terms: geometric extent,...
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
eV
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
EW
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.

Photonics DictionaryE

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