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Photonics Dictionary

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unmanned aerial vehicle
An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without a human pilot onboard. UAVs are remotely controlled or autonomously operated, and they can be used for various...
unpolarized
Behaving as though characterized by a series of waves having planes of vibration oriented at all possible azimuths.
UOE
unit of error
UPC
universal product code
upper rim ray -> rim ray
A ray of an image-forming bundle that passes through the edge of the entrance pupil or aperture stop. Usually used in connection with meridian rays, an upper rim ray is one that passes through the...
URA
uniformly redundant array
USAS-CSOCR
USA standard character set for optical character recognition
USB
universal serial bus
USITC
US International Trade Commission
USRA
University Space Research Association
USTA
US Telecommunications Association
UT
universal time
UTC
universal time corrected
UTM
universal transform mercator
uviol glass
A type of glass contrived by Schott that is highly transparent to ultraviolet radiation.
v-coat
A multilayer antireflective thin-film coating, so called because its reflectance rises steeply at wavelengths above and below a narrow band at zero. The v-coat is particularly useful in high-power...
V-groove
A V-shaped channel pressed or etched into a substrate, in which, for example, optical fibers may be placed to create an integrated optical component.
V-number -> normalized frequency
Also referred to as the V number in fiber optics; the normalized frequency is a dimensionless quantity, denoted by the symbol V, given by: where a is waveguide core radius, l is wavelength in vacuum,...
vacancy
In an ionic crystal, the region in the crystal lattice where the ion, predicted to be present, is absent.
vacuum
In optics, the term vacuum typically refers to a space devoid of matter, including air and other gases. However, in practical terms, achieving a perfect vacuum, where there is absolutely no matter...
vacuum apparatus
Equipment dependent on the effects of a vacuum. The principal applications in optics are in the coating of lenses and substrates and the fabrication of multilayer interference filters.
vacuum breaker
A valve that serves to release air into an evacuated system.
vacuum chamber
A vacuum chamber is a sealed enclosure from which air and other gases are removed to create a low-pressure environment, typically close to or at a complete vacuum. These chambers are often...
vacuum etching
Also known as cathodic etching. Surface etching achieved by bombarding an evacuated surface with gas ions.
vacuum gauge
A gauge designed to measure the degree of vacuum in an evacuated vessel. A simple U-tube containing mercury is adequate for low vacua, but for high vacua other methods must be employed. See McLeod...
vacuum phototube
A phototube that functions within a vacuum and thus eliminates the effects of gaseous ionization on its electrical properties.
vacuum spectrograph
A spectrograph that functions in a vacuum and therefore eliminates any air-absorption of the emission being surveyed.
vacuum spectrography
The technique of producing spectrograms in wavelengths beyond 120 nm by the use of a diffraction grating and a Schumann plate in a vacuum environment.
vacuum ultraviolet detector
A device that serves to detect the presence of vacuum ultraviolet radiation. It may be photographic film, a thermopile, ion chamber, vacuum photodiode, photomultiplier or channel electron multiplier.
vacuum ultraviolet radiation
Radiation whose spectrum runs between 100 and 300 nm. Any work with these wavelengths requires evacuated equipment.
vacuum ultraviolet source
Any source that emits radiation of wavelengths between 100 and 300 nm. Instruments used to study these sources must be evacuated, as vacuum ultraviolet does not travel freely in air.
vacuum ultraviolet spectroscopy
A method of spectral analysis using wavelengths between 100 and 300 nm that utilizes both emission and absorption techniques.
VAD
vapor axial deposition
valence band
In a crystalline substance, the spectral range of states of energy that contains the crystal's binding valence electrons.
valence crystal
A crystal that is held together by covalent bonds.
VAMP
visual-acoustic-magnetic pressure
Van der Waals
Van der Waals forces refer to the attractive or repulsive forces between molecules (or parts of molecules) that arise from fluctuations in electron distribution. These forces are relatively weak...
vanadate laser
Lasers based on neodymium-doped yttrium or gadolinium vanadate crystals. These include yttrium vanadate (Nd:YVO4), gadolinium vanadate (Nd:GdVO4), and lutetium vanadate (Nd:LuVO4). Vanadate lasers...
vapor degreasing
A method of cleaning and drying coated optical components. The cooled parts are placed in a container above a boiling solvent, whose vapors condense on the parts. When the parts reach the temperature...
vapor-phase axial deposition
A process by which high-quality fiber optics are made. See axial vapor-phase deposition.
vapor-phase epitaxy -> epitaxy
A well controlled thin films technique for growing films with good crystal structure in ultra high vacuum environments at very low deposition rates. Epitaxy methods are well known for the growing of...
vapor-phase oxidation
See inside vapor-phase oxidation; outside vapor-phase oxidation.
VAR
visual aural range
varactor
A semiconductor diode that exhibits change in capacitance with a change in applied voltage; used as a voltage-variable capacitor.
variable-speed scanning
A scanning technique in which the optical density of the film being scanned controls the speed of deflection of the scanning beam.
VCASS
visually coupled airborne systems simulator
VCD
variable-capacitance diode
VCF
voltage-controlled frequency
VCSEL -> vertical-cavity surface-emitting laser
A vertical-cavity surface-emitting laser (VCSEL) is a type of semiconductor laser diode that emits light vertically from the surface of a semiconductor wafer. VCSELs are commonly used in various...
VDC
volts direct current

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