8,738 terms
Photonics Dictionary
Search 8,700+ definitions in the Photonics Dictionary—your authoritative source for terms in optics, lasers, imaging, fiber optics, and related technologies.
APDavalanche photodiode
APD detectorAn 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...
apertometerAn instrument designed to measure the numerical aperture of an objective.
apertureAn opening or hole through which radiation or matter may pass.
aperture cardA 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 diaphragmThe second adjustable iris diaphragm in an optical system. In the common microscope condenser system, it usually is located beneath the substage condenser on a transmitted light microscope. When the...
aperture distortionA loss of resolution or detail in a television signal caused by the size of the electron scanning beam.
aperture illuminationThe amplitude, polarization and phase contained in the field distribution over the aperture.
aperture imagingThe formation of an image by a pinhole aperture that transmits radiation, such as gamma radiation.
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 ratioThe ratio of the lens aperture to its focal length (1/f/#).
aperture stopA physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.
aphelionThe point of a planet or comet's orbit that is farthest from the sun.
APIapplication programming interface
APLaverage picture level
aplanatAlso known as aplanatic lens. A lens corrected for spherical aberration and coma.
aplanatic lens systemA system that satisfies the Abbe sine condition, and is free from 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...
apochromatic systemAn optical system that is corrected chromatically for three colors simultaneously.
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...
apogeeThe point on an elliptical orbit about the Earth that is the farthest distance from the Earth.
APOMAAmerican Precision Optics Manufacturers Association
apostilbA unit of luminance equal to 1/p candela per square meter.
apparent contrastThe perceived brightness difference between light and dark areas on a target.
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 luminanceThe perceived brightness of an object being viewed at some distance, especially through an optical instrument.
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
APTautomatic picture transmission
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...
arc light sourceIn 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...
arc spectrumThe spectrum of the light produced by vaporizing an element in an electric arc.
arcuate displacementDisplacement 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...
AREactivated reactive evaporation
area concentrationThe ratio of aperture area over receiving area for a specific lens. Also called geometric concentration.
area image sensor -> mosaic detector arrayA group of photosensors arranged in a grid-like pattern covering the entire field of view, enabling them to record it all at once (as a camera records an image on film) rather than by scanning parts...
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 UV...
argon-ion lasergas laser using ionized argon as the active medium and applying electronic excitation in order to produce the laser light
ARLacceptable reliability level
ARMantiradiation missile
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.
Photonics Dictionary