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Photonics Dictionary: A

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aspect of image
The particular orientation of the image, such as normal, canted, inverted or reverted.
aspect ratio
With 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.
aspheric
Not 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 lens system
An optical system having one or more lens or mirror components that have nonspherical surfaces. These surfaces, whether reflecting or refracting, serve to advance or retard the incident wavefront,...
aspheric lens
An 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 mirror
An 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...
aspherizing
The modification of the spherical surfaces in an optical system to correct for spherical aberration.
assist gas
A 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 difference
In an optical system having astigmatism, the distance between the tangential and sagittal image planes.
astigmatic spectral line
In an astigmatic grating, the image of the entrance slit located at the primary focus.
astigmatism
A lens aberration that results in the tangential and sagittal image planes being separated axially.
astigmatizer
A cylindrical lens that may be rotated to distort a bundle of light originating at a point source, to form a line image.
ASTM
American Society for Testing and Materials
Aston dark space
In the discharge of a vacuum tube, the narrow, nonluminous region that sometimes may be found between the cathode and its glow.
astrometry
The analysis and measurement of celestial bodies, their motions and positions.
astronomical camera
A camera designed to record astronomical objects (e.g., stars, planets, nebulae, galaxies) and their spectra.
astronomical mirror
An astronomical mirror, also known as a telescope mirror or primary mirror, is a key component of a reflecting telescope. It serves as the primary optical element responsible for gathering and...
astronomical observatory
A facility designed for the observation and recording of astronomical phenomena.
astronomical photography
The use of photographs to record astronomical objects and phenomena for purposes of physical observation and measurement of motion, radiation and spectra.
astronomical scintillation
Any irregular motion, variation in intensity or change in color that arises because of atmospheric turbulence during the observation of an astronomical phenomenon or object.
astronomical spectrograph
An instrument that photographs the spectra of an extraterrestrial object.
astronomical spectroscopy
The process of using a spectrograph with a telescope to acquire information on an astronomical object's speed and physical characteristics.
astronomical telescope
An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial objects for observation and analysis. It typically consists of two main optical...
astronomical unit
The unit generally used to express distances within the solar system, and sometimes to measure interstellar distances. Technically, one astronomical unit is the mean distance between the Earth and...
astronomy
The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies...
Astrosital
A glass-ceramic material developed in Russia. Astrosital resembles Zerodur in terms of its ultralow thermal expansion. Other spellings include Astro-Sital and Astro-Sitall.
asym
asymmetric
asymptotic spectral reflectance
The unchanging nature of spectral reflectance as vegetational density increases to the point where additional increases in leaf area index or biomass do not cause a change in the spectral reflectance.
asynchronous transfer mode
A method of data multiplexing that can provide large, instantaneous bandwidths for busy traffic while permitting slow traffic to use that bandwidth between bursts. Very short, fixed-length packets or...
asynchronous transmission
A mode of data transmission whereby each bit of information is generated separately, with some stop/start code to indicate the interval between bits.
AT
atomic time
ATARS
advanced tactical air reconnaissance system
ATDM
Asynchronous Time Division Multiplexing
ATE
automatic test and evaluation
ATLIS
automatic tracking laser illumination system
ATM
asynchronous transfer mode
atmos
atmosphere
atmospheric absorption line parameters compilation
Compilation of the Air Force Cambridge Research Laboratories that contains values of the line parameters of the 1-0 bands of 12C16O. Because of the high accuracy of this record, calculated spectra...
atmospheric attenuation
The reduction in luminance of a light beam due to absorption and scattering as it passes through the atmosphere.
atmospheric inhomogeneities
Localized variations in the purity and the index of refraction of the atmosphere.
atmospheric optics
The analysis of the properties of radiation, such as light, when acted upon by variations in the atmosphere. Blue and red skies, along with ice halos, glories, coronas and rainbows can all be...
atmospheric refraction correlation
Formulaic compensation to correct laser ranging data for the effects of horizontal refractivity gradients; it requires the horizontal pressure and temperature gradient at laser sites, which are...
atmospheric turbulence
Irregularities and disturbances in the atmosphere that are of particular interest because they induce random temporal and spatial phase and amplitude fluctuations that destroy the optical quality and...
atmospheric window
A range of wavelengths within which radiation transmitted through the atmosphere suffers relatively little absorption by atmospheric gases.
atom optics
The area of optics in which the wave nature of a particle is exploited to carry out very accurate interferometry and other optical techniques with atoms instead of photons. In this process, particles...
atomic absorption spectrometer
An atomic absorption spectrometer (AAS) is an analytical instrument used to determine the concentration of specific chemical elements in a sample by measuring the absorption of light at...
atomic absorption spectroscopy
The analysis of the atomic structure of a sample by means of a source radiation that is absorbed and emitted by the sample with lines corresponding to the number and arrangement of atoms. Generally a...
atomic clock
An atomic clock is a highly precise timekeeping device that uses the vibrations or oscillations of atoms as a reference for measuring time. The most common type of atomic clock uses the vibrations of...
atomic emission spectrometry
Spectrometric analysis of the distinct and characteristic spectra of atoms of elements. The atoms are energized to emit radiant energy, which, when dispersed by a prism or diffraction grating,...
atomic fluorescence spectroscopy
The analysis of fluorescence emitted by discrete atoms, in flames, that have absorbed radiation from an external source. It is used to study the physical and chemical processes that arise from...

Photonics DictionaryA

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