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Photonics Dictionary: V

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veiling glare
Diffuse stray light at the image plane of an optical system that results in reduced contrast and resolution.
velocimeter
See laser Doppler velocimeter; laser velocimeter.
velocity modulation laser spectroscopy
A method of measuring negatively charged phase ions using a color-center or lead-salt diode laser.
venetian-blind effect
Short-distance scattering of light in holography caused by random index inhomogeneities and the developing index that interferes with the incident beam, thus recording a hologram of the scattered...
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 acuity
The degree to which a pair of fine lines can be aligned to each other. A normal observer will demonstrate an accuracy of 10 arc seconds and a repeatability of 5 arc seconds.
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.
vertex power
The reciprocal of the back focal distance of a spectacle lens.
vertical air photograph
An aerial photograph produced when the optical axis of the camera is perpendicular to the surface below.
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 imbalance
The difference in base up or down prism power at corresponding points located on the two lenses of a pair of spectacles.
vertical incident illumination
With respect to microscopy, light that is directed down through the objective onto the specimen and then returned by reflection.
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 transmitted illumination
With respect to microscopy, light that is directed through the specimen by a substage condenser.
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.
vertometer
A device that measures the back focal length or vertex power of a lens.
very high frequency
The frequency band from 30 to 300 MHz. The corresponding wavelengths are from 1 to 10 m. (VHF).
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...
very low frequency
The frequency band from 3 to 30 kHz. The corresponding wavelengths are from 10 to 100 km. (VLF).
vesicular image
An image with variations in density due to the differential scattering ability of microscopic bubbles in a transparent layer.
VF
voice frequency
VGA
video graphics array
VHF
very high frequency
VHSIC
very high-speed integrated circuit
via
In integrated circuits, a pathway, hole, or other passage through the substrate.
vibrational circular dichroism
Vibrational circular dichroism (VCD) is a spectroscopic technique used to probe the chiral properties of molecules. It measures differences in the absorption of left- and right-circularly polarized...
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.
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 amplifier
A wideband amplifier used to process video or picture information.
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.
video graphics array
A display standard no longer in use and originally defined for IBM PCs, with 640 3 480 pixels in 16 colors and a 4:3 aspect ratio. There is also a text mode with 720 3 400 pixels. The standard has...
video measuring gauge
A device that calibrates the size, position or distance of objects imaged on a video screen.
video scan converter
A device that changes the number of lines per frame of a video image to adapt to a lower resolution format, either by deleting lines, compressing lines or by imaging only a part of the original...
video subtractor -> image comparison
A method used in imaging to detect subtle differences between two apparently similar pictures. It can be achieved by superimposing the negative of one photograph over a contact print of another, by...
video-intensified microscopy
The observation of specimens by a microscope linked to a television camera and an image processor.
videodisc
A disc whose surface contains recorded digital data at high-packing densities arranged in concentric rings. The data, representing video frames, are both recorded and read by a laser beam.
videography
Videography refers to the process of capturing moving images and recording them in a digital format. It involves the use of video cameras, lighting equipment, and audio recording devices to create...
vidicon
A small television tube originally developed for closed-circuit television. It is about 1 inch in diameter and 5 inches long. Its controls are relatively simple and can be operated by unskilled...
view camera
A camera that permits adjustments in the perspective of an image; this is accomplished by the camera design, which permits tilt, swing, rise or fall of the image transmitted. Also known as a...
viewfinder
A device, optical or electronic, that may be joined to a camera so that the operator may perceive the scene as the camera does.

Photonics DictionaryV

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