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Photonics Dictionary: A

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Angstrom mode
An operational mode for radiometers that analogs the method of operation of an angstrom pyrheliometer. In this mode, the rearward-facing cavity is electrically heated, while the forward cavity is...
angstrom
An angstrom, symbolized by the Ångström or Å, is a unit of length used to express atomic and molecular dimensions. It is equal to 0.1 nanometers or 1 × 10-10 meters. The...
angular aperture
The angle between the most divergent rays that can pass through the lens to form an image. In a birefringent crystal light modulator or Pockels cell, the maximum angle in the incident light rays that...
angular misalignment
Angular deviation from the optimum alignment of source to optical waveguide, waveguide to waveguide, or waveguide to detector, resulting in a loss of optical power.
angular spectrum approach
The angular spectrum approach is a mathematical and computational technique used in the field of optics to analyze and simulate the propagation of optical waves, particularly in the context of wave...
angular tracking
A laser radar application in which a sequence of direct measurements of target position is fed into a tracking filter to produce refined estimates of both present and future target positions.
anisophotic source
A light source that emits an uneven distribution of radiant energy through the visible range.
anisotropic
Anisotropic is a term used to describe a material or substance that exhibits different properties or behaviors in different directions. In other words, the physical or mechanical characteristics of...
anisotropy
Anisotropy refers to the property of exhibiting different values or characteristics when measured in different directions. In various fields, including physics, materials science, and geology,...
ANMC
American National Metric Council
annealing
The process of heating and slowly cooling a solid material, like glass or metal, to stabilize its thermal, electrical or optical properties or, as in semiconductor materials, to reverse lattice...
annular eclipse
A type of solar eclipse that occurs when the sun is at perihelion and the moon is at apogee. Because the apparent size of the moon is insufficient to cover the sun, the outer edge of the solar disc...
anomalous photoconductivity
A spectral phenomenon in which the degree of the photoresponse of an illuminated semiconductor is determined by the wavelength composition of the incident light.
anomalous trichromatism
Color vision whereby abnormal proportions of three colors are needed for color matching.
ANRT
Association Nationale de la Recherche Technique
ANSI
American National Standards Institute
antialiasing
In image processing, methods of reducing image defects that result from false data. Techniques include sampling, linear intensity, filtering a high-resolution image to produce a low-resolution image,...
antibleaching
Characteristic of an absorber in the IR region, whereby absorption increases as a direct function of the intensity of the incident, continuous radiation.
anticathode -> x-ray tube target
Also known as an anticathode. An electrode or electrode section that is focused upon by an electron beam and that emits x-rays.
antiferromagnetism
The elimination of magnetic moments and decrease in magnetic susceptibility with a decrease in temperature due to the equal power of atomic magnets.
antifog coating
A coating that is capable of stopping the condensation of moisture on an optical surface.
antigen
An antigen is any substance that is capable of triggering an immune response in an organism. Antigens are typically proteins or large polysaccharides, although other types of molecules can also act...
antiguide
A waveguide that has a core with a lower refractive index than the refractive index of the cladding. This structure can limit the power of the transmitted beam by removing unwanted radiation, for...
antiresonance
Literally the opposite of resonance, antiresonance occurs when any variation in excitation frequency results in an increased response.
antisolar point
The point to which the extension of the straight line, reaching from the sun to the observer's eye after penetrating the atmosphere of the Earth, is projected.
ANVIS
aviator's night vision imaging system
AOI
area of interest; automatic optical inspection
APCVD
atmospheric pressure chemical vapor deposition
APD detector
An APD detector, or avalanche photodiode detector, is a type of photodetector used to detect light or optical signals by converting incoming photons into electrical current. It operates based on the...
aperture
An opening or hole through which radiation or matter may pass.
aperture card
A combination 80-column computer card containing a 35-mm microfilm frame. Reference data can be punched onto the card to facilitate retrieval of it on film.
aperture imaging
The formation of an image by a pinhole aperture that transmits radiation, such as gamma radiation.
aperture mask
Also known as a shadow mask, a perforated plate placed between the focusing and accelerating electrodes, and the tricolor phosphor screen in a color-television tube.
aperture stop
A physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.
API
application programming interface
aplanat
Also known as aplanatic lens. A lens corrected for spherical aberration and coma.
aplanatic lens system
A system that satisfies the Abbe sine condition, and is free from spherical aberration and coma.
aplanatic points
Aplanatic points refer to specific points in an optical system where certain aberrations, such as spherical aberration or coma, are minimized or eliminated. In an optical system, aberrations are...
aplanatic surface
An aplanatic surface is an optical surface that is specifically designed or shaped to minimize spherical aberration and coma. Spherical aberration is an optical aberration that occurs when light rays...
apochromat
An apochromat, often referred to as an apochromatic lens or apochromatic objective, is a type of optical system designed to minimize chromatic aberration. Chromatic aberration occurs when different...
APOMA
American Precision Optics Manufacturers Association
apparent movement
The visual perception of motion when fixed stimuli are exposed in rapid temporal and spatial succession.
APT
automatic picture transmission
aptamer
An aptamer is a short, single-stranded DNA or RNA molecule that can bind to a specific target molecule with high affinity and specificity. Aptamers are often referred to as chemical antibodies due to...
aqueous humor
The transparent fluid that fills the portion of the eye between the cornea and the eye lens (the anterior chamber).
AR
Abbe refractometer; acoustic radiometer; acoustic resonance; active region; alpha ray; amplitude ratio; antireflective; aperture ratio; applied research; argon; aspect ratio; atomic reactor; augmented reality
Arago spot
A bright spot or point, due to Fresnel diffraction, that appears at the center of the shadow of a circular object in light originating from a point source. Also referred to as a Fresnel spot or...
arc flash
An arc flash is a sudden release of electrical energy due to an electric arc — a continuous, high-current discharge of electricity between conductors or from a conductor to ground. Arc flashes...
arc light source
In present usage, especially for spectroscopic identification, an arc between electrodes that serves as a radiation source. Gas tubes that contain mercury vapor and mixtures of helium, neon and argon...
arcuate displacement
Displacement in a direction perpendicular to that of the intended displacement, as in a translation stage with simple flexures that experiences vertical displacement during horizontal motion; it is...

Photonics DictionaryA


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