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3,377 terms

Photonics Dictionary

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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...

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...

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...

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...

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...

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...

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...

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.

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...

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....

varifocal -> variable-focus lens

VCF

voltage-controlled frequency

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.

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...

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 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

via

In integrated circuits, a pathway, hole, or other passage through the substrate.

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 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 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-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...

vignetting

In an optical system, the gradual reduction of image illuminance as the off-axis angle increases, resulting from limitations of the clear apertures of elements within the system.

VIP

virtual image processing

virtual base

The product of the actual base or baseline of a rangefinder or heightfinder, and the power or magnification of the instrument.

virtual histology

Virtual histology refers to the use of digital technology and computational methods to simulate or recreate histological images and structures without the need for traditional physical slides and...

virtual reality

Virtual reality (VR) is a computer-generated simulation of a three-dimensional environment or experience that can be interacted with and explored by an individual using electronic devices, such as a...

virtual retinal display

The use of miniature scanners to project raster-scanned video images directly onto the surface of the human retina, eliminating the need for a projection surface.

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...

visual acuity

The numerical definition of the ability of an observer to perceive fine detail. The average value may be taken as one minute, or 6.7 cycles/mm, at 250 mm (normal viewing distance).

visual binaries

A pair of stars (double star) that can be seen separately with a telescope, generally by setting a filar micrometer for the separation and position angle. Observation of visual binaries improves with...

Photonics Dictionary