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Photonics Dictionary

ultrasonic light diffraction
The optical diffraction spectra formed, or the method that produces them, when a light beam is transmitted through a longitudinal sound field.
ultrasonic light modulator
An instrument with a fluid that modulates a light beam traversing it because of the effect of ultrasonic waves passing through the fluid.
ultrasonic stroboscope
A light-interference device whose excitation is determined by the modulation of a light beam by an ultrasonic field.
ultrasonic
Ultrasonic refers to sound waves with frequencies higher than the upper audible limit of human hearing, typically above 20,000 Hz. These waves are termed ultrasonic because they are beyond the range...
ultraviolet A
The region of the electromagnetic spectrum from 320 to 400 nm.
ultraviolet absorbing filter
A filter that is opaque from 200 to 400 nm.
ultraviolet B
The region of the electromagnetic spectrum from 280 to 320 nm.
Ultraviolet-C
Ultraviolet-C (UV-C) refers to a specific range of ultraviolet radiation with shorter wavelengths than those of visible light. UV-C radiation spans the electromagnetic spectrum with wavelengths...
ultraviolet densitometry
A technique, involving spectrophotometry in the ultraviolet, that is designed to determine the colors of thin-layer chromatographic absorbents after elution.
ultraviolet fiber optics
Ultraviolet (UV) fiber optics refers to optical fibers that are designed and optimized for the transmission of ultraviolet light, which is electromagnetic radiation with wavelengths shorter than...
ultraviolet lamp
A type of lamp that emits a high quantity of ultraviolet radiation. This may be an arc lamp encased in a bulb of a glass that is transparent to ultraviolet rays.
ultraviolet lens
A lens intended for use with wavelengths shorter than about 380 nm. It must be made of quartz, calcium fluoride, lithium fluoride or some other material transparent to ultraviolet radiation, as glass...
ultraviolet lens
A microscope used either to detect selective absorption of various wavelengths by the specimen or to achieve increased resolution by virtue of the short wavelength of ultraviolet radiation. Electron...
ultraviolet microscopy
The study and photographing of microscope specimens in ultraviolet light; using an optical microscope containing fluorite and quartz components to efficiently image wavelengths much shorter than the...
ultraviolet molecular nitrogen laser
A pulsed laser having molecular nitrogen as laser material and a wavelength output of 337 nm in the ultraviolet region. It is essentially a channel flashtube in which a pulse is applied to the...
ultraviolet photoemission spectroscopy
A technique for measuring the energy spectrum of electrons emitted during the absorption of ultraviolet radiation. This spectrum reveals the characteristic ionization energies of the molecules and...
ultraviolet photomicrography
The photographic recording that uses ultraviolet radiation to irradiate the microscope sample being examined and to form an image of the object on a photographic medium. The components of the...
ultraviolet reflectance
Ultraviolet reflectance refers to the ability of a material or surface to reflect UV light. Ultraviolet light is electromagnetic radiation with wavelengths shorter than those of visible light,...
ultraviolet spectrometer
A spectrophotometer designed for use in the 200- to 380-nm range of the electromagnetic spectrum and equipped with a calibrated scale to determine wavelength.
ultraviolet
That invisible region of the spectrum just beyond the violet end of the visible region. Wavelengths range from 1 to 400 nm.
ultraviolet-visible spectrometer
Also known as UV-VIS spectrometer, a device that measures the absorbance, reflectance or transmittance of light in the ultraviolet or visible wavelengths absorbed, reflected or transmitted. Commonly...
umbilical
A connection, typically made up of one or more cables, between a laser head and a separate power supply. Flexible pipes or hoses are sometimes used to protect and stabilize multiple cables.
umbra -> penumbra
A source of light will not cast a distinct shadow of an interfering, opaque object, but will cast a shadow having two parts: 1. the umbra, or the central, totally dark part of the shadow; and 2. the...
unblanking
The initiation of the beam in a cathode-ray tube.
unblocking
The process whereby optical elements are removed from a block.
uncut
A term describing lenses with both surfaces finished but not yet cut to any form.
underillumination
Illumination of hologram facets with a beam that covers only a small portion of the hologram in order to optimize laser energy use. See overillumination.
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...

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