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75 terms
Photonics Dictionary: V
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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.
vesicular image
An image with variations in density due to the differential scattering ability of microscopic bubbles in a transparent layer.
VHSIC
very high-speed integrated circuit
vibrational transition
A vibrational transition refers to a change in the vibrational energy of a molecule. Molecules consist of atoms that are connected by chemical bonds, and these atoms are not stationary but are in...
vibronic transition
A type of change in the energy levels of molecules in a laser that results in lasing action. Vibronic transitions are those between one electronic level and another.
video-intensified microscopy
The observation of specimens by a microscope linked to a television camera and an image processor.
visibility
The maximum distance at which the eye can perceive and evaluate objects.
visibility meter
1. An instrument used to determine the visual range in an environment. 2. A type of photometer that artificially reduces an object's visibility to threshold limits and records the quantity of...
visible spectrum
That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to 750 nm in wavelength.
visible
That term pertaining to the spectral region that can be perceived by the eye.
visioceilometer
An instrument that uses an erbium:glass laser to determine cloud height from the ground.
vision
The processes in which luminous energy incident on the eye is perceived and evaluated.
visually coupled airborne systems simulator
A visual system including a tiny television tube and imaging optics, all contained in a helmet to be worn by pilots in flight simulator training.
vitreous silica
->
fused silica
Glass consisting of almost pure silicon dioxide (SiO2). Also called vitreous silica. Frequently used in optical fibers and windows.
VLSI
very large scale integration
voltage contrast analysis
A nondestructive testing method for very large scale integration circuits, using a scanning electron microscope to monitor changes in the electronic state of the chip as it is fed test voltages while...
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...
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 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 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 spectrograph
A spectrograph that functions in a vacuum and therefore eliminates any air-absorption of the emission being surveyed.
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...
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.
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
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....
VCASS
visually coupled airborne systems simulator
VDM
vapor density monitoring
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...
veiling brightness
A brightness, superimposed on the image of the retina, that decreases its contrast and that often results in decreased visibility.
velocity modulation laser spectroscopy
A method of measuring negatively charged phase ions using a color-center or lead-salt diode laser.
vernier interferometer
A phase-shift interferometer used to detect the relative angular speeds or positions of two concentric rotors.
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 resolution
In television system specifications, the number of parallel horizontal black and white lines of equal thickness, that can be resolved from top to bottom of the raster. (One line equals either a black...
vertical retrace
With respect to television, the returning direction of the electron beam during the vertical blanking period.
vertical-cavity laser diode
A type of surface-emitting laser diode that uses dielectric mirrors to produce surface emission. The laser cavity is established in a vertical direction with respect to the plane of the active region.
vertical-cavity surface-emitting laser
->
vertical-cavity laser diode
A type of surface-emitting laser diode that uses dielectric mirrors to produce surface emission. The laser cavity is established in a vertical direction with respect to the plane of the active region.
vertical-deflection electrodes
Two electrodes that shift the electron beam vertically on a cathode-ray tube screen using electrostatic deflection.
very long baseline interferometry
Consists of a pair of radio telescopes concentrated on a single celestial object. This technique creates a single radio telescope with a diameter equal to the distance between the pair, which allows...
Vickers microhardness test
A test similar to the Knoop hardness test, but used for fractured material. The indenter is a square-based pyramid-shaped diamond.
VIDAT
visual data acquisition
video
Referring to the bandwidth and spectrum location of the signal produced by television or radar scanning.
video detector
A device, such as a thermionic or crystal diode, that is introduced into the vision channel of a television receiver to select the signal from the intermediate-frequency carrier.
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Photonics Dictionary
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