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5,098 terms

Photonics Dictionary

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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

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.

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 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...

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.

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.

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...

USAS-CSOCR

USA standard character set for optical character recognition

USITC

US International Trade Commission

USRA

University Space Research Association

USTA

US Telecommunications Association

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-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,...

V-value -> Abbe constant

A dispersion relation defined in order to value the reciprocal amount of dispersion. It is defined as the refractivity over the difference in index values of the shortest and longest visible...

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 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 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 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

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 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...

variable-focus condenser

An Abbe condenser in which the upper lens element is fixed. The lower lens may focus the illumination between the elements so that it emerges from the fixed lens as a large-diameter parallel bundle....

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.

veiling glare

Diffuse stray light at the image plane of an optical system that results in reduced contrast and resolution.

Verdet constant

A factor of an equation of the Faraday effect, which is the rotation of the plane of light polarization by transparent materials in a magnetic field. Therefore, in the equation: where a...

vergence

The angular relation between two light rays that originated at the same object point. Sometimes used to indicate the angle between the visual axes of the eyes.

vernier interferometer

A phase-shift interferometer used to detect the relative angular speeds or positions of two concentric rotors.

vertex

The point of intersection of the optical axis with any centered optical surface.

vertical blanking

With respect to a television system, a pulse transmitted at the end of each field to break off the cathode-ray beam as it begins the next field.

vertical external cavity surface-emitting laser

A laser that has a surface-emitting semiconductor gain element coupled to an external mirror designed to complete the laser resonator. VECSELs can be electrically or optically pumped. The extended...

vertical leveling mirror

A two-sided mirror suspended by a pendulum mechanism. An autocollimator set normal to such a mirror surface will, by definition, have its optical axis set horizontal.

vertical retrace

With respect to television, the returning direction of the electron beam during the vertical blanking period.

Photonics Dictionary