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Photonics Dictionary: A

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airglow
Diffuse light emitted by the atmosphere due to the excitation of particles of atmospheric gas. These excited particles release light that is visible from Earth as a faint luminescence in the night...
AIRS
automatic image retrieval system
Airy differential equation
The equation devised by Sir G.B. Airy for the analysis of light diffraction near a caustic surface: (d2f/dz2) - zf = 0 where z represents the independent variable, and f is the value of the function.
Airy disc
The central peak (including everything interior to the first zero or dark ring) of the focal diffraction pattern of a uniformly irradiated, aberration-free circular optical element or system.
AIS
acoustic imaging system
albedo
The ratio of radiant energy reflected from a rough surface to that incident on it. Usually, the radiant energy is total solar energy; thus, it is not a spectral quantity.
ALD
atomic layer deposition
ALE
atomic layer epitaxy
alexandrite
A host crystal for chromium that emits pulsed or continuous-wave laser light, tunable from about 720 to 790 nm.
alexandrite lasers
An alexandrite laser is a solid-state laser that utilizes a synthetic crystal made from the rare earth element alexandrite (BeAl2O4:Cr3+). This crystal is capable of emitting laser light in the...
ALF
airborne laser fluorosensor
algorithm
A precisely defined series of steps that describes how a computer performs a task.
ALIAS
adaptive learning image analysis system
aliasing
In image processing, the result of a sampling frequency that is too slow to preserve the spatial frequencies of the image. When detail has a frequency greater than half the sampling frequency, it...
alidade
An old name for the rotating arm moving about an axis of rotation over a divided circle used to measure angles. Now the term refers to a small stadia telescope mounted over a ruler for use in...
aligned bundle
An assembly of fibers in which the coordinates of each fiber are the same at the two ends of the bundle. Also called coherent bundle.
alignment laser
A laser, usually employing helium-neon or other gases as the active medium, used for alignment in industrial applications.
alignment telescope
An optical tooling instrument consisting of an objective lens, a focusing lens, an optical micrometer, a reticle and an eyepiece. The alignment telescope projects a precise line of sight to which a...
all-silica fiber
Also known as all-glass fiber. A fiber with both a silica core and a silica cladding, regardless of the presence of a polymer overcoat or buffer.
allochromy
Any fluorescence in which the wavelength of the emitted light differs from that of the absorbed light.
allogyric birefringence
Left- and right-hand circularly polarized beams that are produced at different velocities by passing plane-polarized light through an optical substance. When recombined, they exhibit different phases...
alloy-junction photocell
A photocell having an alloy junction formed by combining an indium disc with a thin wafer of N-type germanium.
allyl diglycol carbonate
Commonly known as CR39, this thermosetting plastic is used in the casting of eyeglass lenses because of its toughness and clarity.
ALP
advanced lightwave platform
alpha
In computer imaging, a value representing opacity.
alpha laser
A 2-million W, 2.7-µm-wavelength hydrogen-fluoride laser used as a directed energy weapon.
alpha particle
A positively charged particle emitted from the nucleus of an unstable isotope, characterized by two protons and two neutrons. Quantitatively, the equivalent of a helium atom's nucleus.
alphanumeric display
A luminous display of numbers and the letters of the alphabet.
alphanumeric generator
In computer graphics, a character generator that produces alphabetical and numerical characters with some punctuation and symbols.
alphanumeric reader
An instrument that reads alphabetic, numerical and special characters by means of a photosensor that measures the varying intensity of the characters reflected from a light source.
alt
altitude
altazimuth
A type of telescope mount that permits direct azimuth and elevation adjustments.
alternating current
Alternating current (AC) is an electrical current in which the direction of flow of electric charge periodically reverses. This reversal occurs at regular intervals, typically in a sinusoidal...
ALU
arithmetic logic unit
aluminized cathode-ray tube
A cathode-ray tube having a screen that is coated on the back with a thin film of aluminum, which serves to intensify the propagation of light.
aluminizing
The process of applying a film of aluminum to a surface, usually by evaporation in a vacuum.
AM
active matrix; air mass; amplitude modulation
AM-LCD
active-matrix liquid crystal display
ambient light
Light present in the environment around a detecting or interpreting device, especially a machine vision system, and generated from outside sources. Such light must be treated as noise by the vision...
ambient noise
The all-encompassing noise associated with a given environment, usually being a composite of a number of sources, far and near.
ambient temperature
The prevailing temperature in the immediate vicinity of the object; the temperature of its environment.
ambrotype
The underexposed collodion that is present on a glass negative as a positive when backed with material.
American Association for the Advancement of Science
The American Association for the Advancement of Science (AAAS) is an international non-profit organization dedicated to advancing science, engineering, and innovation for the benefit of all people....
American Astronomical Society
The American Astronomical Society (AAS) is a prominent professional association of astronomers and other scientists dedicated to the study of astronomy and related fields. Founded in 1899, the AAS...
American Chemical Society
The American Chemical Society (ACS) is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 and chartered by the U.S. Congress,...
Amici objective
A form of high-power microscope objective.
Amici prism
Also known as roof prism. A type of prism designed by G.B. Amici. It consists of a roof edge produced upon the long reflecting face of a right-angle prism. Used as an erecting system in elbow and...
ammonia maser
An ammonia maser is a device that amplifies microwave radiation using ammonia gas molecules in a process analogous to how lasers amplify visible light through stimulated emission of radiation. The...
ammonia pellets
Charged frozen pellets that are rapidly bombarded with a focused high-power laser to form a dense plasma that can be heated and sustained with neutral beams.
AMOLED
active-matrix organic light-emitting diode

Photonics DictionaryA

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