6,181 terms
Photonics Dictionary
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aperture maskAlso 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 stopA physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.
APIapplication programming interface
aplanatAlso known as aplanatic lens. A lens corrected for spherical aberration and coma.
aplanatic pointsAplanatic 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 surfaceAn 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...
apochromatAn 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...
apodizationThe use of a variable transmission filter at the aperture stop of a lens to modify its diffraction pattern. Reduced transmission at the center of the aperture will favor performance at high...
apostilbA unit of luminance equal to 1/p candela per square meter.
apparent fieldThe angular subtense of the field of view in the image space of a telescope, as differentiated from that in the object space (the true field).
apparent movementThe visual perception of motion when fixed stimuli are exposed in rapid temporal and spatial succession.
apparent visual angleThe angle subtended by an object, determined by the size of the object and its distance from the viewer.
APSactive pixel sensor; active pixel system; Advanced Photon Source; American Physical Society; atom probe spectroscopy; autocorrelated photon spectroscopy
aptamerAn 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 humorThe transparent fluid that fills the portion of the eye between the cornea and the eye lens (the anterior chamber).
ARAbbe refractometer; acoustic radiometer; acoustic resonance; active region; alpha ray; amplitude ratio; antireflective; aperture ratio; applied research; argon; aspect ratio; atomic reactor; augmented reality
Arago spotA 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 dischargeThe electric arc that is a particular discharge between two electrodes in a gas or vapor which is characterized by high cathode densities and a low voltage drop.
arc flashAn 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...
AREactivated reactive evaporation
area scanArea scan, in the context of imaging and cameras, refers to a method of capturing an entire two-dimensional image in a single snapshot or exposure. Unlike line scan, which captures images one line at...
argon-fluoride excimer laserAn argon-fluoride (ArF) excimer laser is a type of ultraviolet laser that operates using a mixture of argon and fluorine gases. Excimer lasers are a class of gas lasers that emit light in the...
armorA protective jacket added to an optical fiber to facilitate use in harsh environments. Armor usually consists of steel or aluminum and is placed between the fiber and its outer jacket.
array processorIn image processing, a specially designed programmable computer peripheral that attaches to the host system for the purpose of more rapid arithmetical calculations than the latter can supply. The...
Arrhenius plotThe plot that expresses a reaction rate vs. the reciprocal of absolute temperature. Often used to describe the thermal characteristics of laser applications such as ablation or annealing.
arsenic trisulfideA dark red opaque material that is transparent to the infrared beyond 1 µm.
artificial radioactivityRadioactivity formed by the bombardment of stable elements by either neutrons or high-energy, charged particles under regulated conditions.
artificial starA point source of light used for the test and evaluation of image quality. May be a backlit pinhole in an otherwise opaque sheet placed at an appropriately large distance from the lens being tested.
ASATantisatellite
ASCIIAmerican Standard Code for Information Interchange
ASDSRSautomatic spectrum display and signal recognition system
ASFIRactive swept frequency interferometer radar
ASIAmerican Standards Institute
ASICapplication-specific integrated circuit
ASIIAmerican Science Information Institute
ASKAautomatic system for kinematic analysis
ASMampere second meter
ASNTAmerican Society for Nondestructive Testing
aspect of imageThe particular orientation of the image, such as normal, canted, inverted or reverted.
aspect ratioWith respect to pictorial displays, the ratio of the width to the height. The television standard in the US is 4:3. High-definition or wide-screen television will have a ratio of 16:9.
asphericNot spherical; an optical element having one or more surfaces that are not spherical. The spherical surface of a lens may be slightly altered so as to reduce spherical aberration. Aspheric surfaces...
aspheric lensAn aspheric lens is a type of lens whose surface profiles deviate from the traditional spherical shape. Unlike spherical lenses, which have a constant curvature across their surfaces, aspheric lenses...
aspheric mirrorAn aspheric mirror is an optical mirror surface that deviates from the shape of a perfect sphere, having a non-spherical surface profile. Unlike traditional spherical mirrors, which have a curved...
aspherizingThe modification of the spherical surfaces in an optical system to correct for spherical aberration.
assist gasA gas, such as oxygen, that improves the speed and efficiency of a laser cutter or welder when applied to the work surface, or an inert gas, such as argon, that helps to clean or shield the work...
astigmatic differenceIn an optical system having astigmatism, the distance between the tangential and sagittal image planes.
astigmatic spectral lineIn an astigmatic grating, the image of the entrance slit located at the primary focus.
astigmatismA lens aberration that results in the tangential and sagittal image planes being separated axially.
astigmatizerA cylindrical lens that may be rotated to distort a bundle of light originating at a point source, to form a line image.
ASTMAmerican Society for Testing and Materials
Photonics Dictionary