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Photonics Dictionary: U

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underwater photography
The field of photography concerned with the recording of subjects beneath the water with a watertight, water-resistant camera system.
underwater television system
A television system designed to obtain pictures of objects or scenes beneath the surface of the water. Generally, a low-light-level television camera and a suitable light source are enclosed in a...
undulator magnet
A device used in a free-electron laser to convert the electron-beam's energy into microwave laser radiation by creating a magnetic field of alternating polarity through which the free electrons are...
uniaxial crystal
A doubly refracting crystal having a single axis along which there is an absence of double refraction.
uniform color space
A color space in which equal distances represent equal visually perceived color differences.
uniform diffuser -> perfect diffuser
A surface that obeys Lambert's cosine law and has a reflectance of unity.
uniform luminance area
In a cathode-ray tube, the region wherein a display on the tube keeps 70 percent or more of its luminance at the center of the viewing area.
uniformly redundant array
Array used in coded-aperture imaging experiments with two-beam CO2 lasers that provide an artifact-free process, faithful reproduction of the true image, and more photon collection than the pinhole...
unijunction transistor
A three-terminal semiconductor having only one PN junction and a stable, open-circuit, negative-resistance property.
unimorph
A piezoelectric transducer made of a thin strip of piezoelectric material bonded to a strip of metal.
uniphase interference
In interferometry, the result of superimposing two wavefronts of identical shape, yielding a uniform intensity interference pattern with no bands.
unipolar
Refers to the transistors in which the working current flows through only one type of semiconductor material, either P-type or N-type. In unipolar transistors, the working current consists of either...
unipotential electrostatic lens
A simple electrostatic lens with a focus controlled by a single potential difference.
unit of error
A unit of measurement in a rangefinder corresponding to 12 s of arc in the apparent field.
unit plane -> principal plane
In a lens or lens system, that surface at which the projections of an entering and exiting ray intersect. Also known as the equivalent refracting surface, the principal plane is most often not...
universal product code
A system by which consumer products are assigned a bar code that is read by a scanner at a cash register, enabling computerization of pricing and inventory records.
universal wavelength function
One of the four functions that allows the computation of a transparent medium's index of refraction, provided the index has been identified for four standard wavelengths.
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.
unstable resonator
A resonator often used for mode control in Fresnel number laser cavities that is highly vulnerable to extremely weak external sources of feedback.
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
UV
ultraviolet
UVFO
ultraviolet fiber optics
uviol glass
A type of glass contrived by Schott that is highly transparent to ultraviolet radiation.

Photonics DictionaryU

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