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8,726 terms

Photonics Dictionary

volt

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,...

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...

voltampere

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

VAFF

variable-aperture far-field

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-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-focus lens

A lens assembly containing several movable elements to permit changing of the effective focal length (EFL). Unlike a zoom lens, a variable-focus lens may require refocusing with each change of EFL....

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.

varifocal -> variable-focus lens

VCASS

visually coupled airborne systems simulator

VCD

variable-capacitance diode

VCF

voltage-controlled frequency

VCR

videocassette recorder

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

VDM

vapor density monitoring

VDU

video display unit

VECSEL

vertical external cavity surface-emitting laser

vector correlation

A machine vision technique of image correlation whereby the correlation kernel (template of the desired image) is transformed into a group of vectors, each representing a specific feature of the...

Vegard-Kaplan bands

The bands found by Vegard in the spectrum of the aurora borealis and by Kaplan in the nitrogen afterglow. They are formed by the effect of metastable nitrogen molecules.

veiling brightness

A brightness, superimposed on the image of the retina, that decreases its contrast and that often results in decreased visibility.

veiling glare

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

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Photonics Dictionary

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