Photonics Marketplace
67 terms

Definitions: U

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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.
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.
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...
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.
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...
uviol glass
A type of glass contrived by Schott that is highly transparent to ultraviolet radiation.

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