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211 terms

Photonics Dictionary: B

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biostimulation

The action of a biological system responding to a single or multiple coherent particles of light produced from a laser source. Examples of laser biostimulation include: retinal interaction of light...

B-scope

A cathode-ray display where information is represented visually as spots. Each spot's location is represented by a horizontal coordinate showing its bearing angle, and a vertical coordinate showing...

Babinet absorption rule

The rule stating that positive uniaxial crystals have greater absorption with respect to the extraordinary component of light, whereas negative crystals have greater absorption for the ordinary...

Babinet compensator

A device containing two opposed quartz wedges of equal angle, one wedge being movable along its length by a micrometer screw. The wedges are cut so that their fast directions are along, and...

Babinet principle

The principle stating that two diffraction screens, one being exactly the negative of the other, will form the same diffraction patterns.

Babinet-Jamin compensator

A Babinet compensator that contains the controlled motion of one prism with respect to the other. This idea was introduced by Jamin.

back channel

A channel for communication with the source in an otherwise unidirectional network, such as a channel that provides interactive features in a cable television network.

back focal length

The distance from the final optic within a system to the rear image point of the system. See focal length.

backlash

In a mechanical system, any lost motion between driving and driven elements due to clearance between parts.

backlight compensation

The ability of a camera to compensate in cases where a subject with a large amount of background light would otherwise be obscured by blooming or silhouetting.

backlighting

The forming of a clear silhouette of an object by placing a light source behind it. Used in machine vision when surface features of an object are not important.

backreflection -> narcissus

A defect in infrared systems that appears as a dark circular area on a displayed image, caused by radiation reflecting into a detector. It can be reduced by low-reflective coatings or by altering the...

backscatter

Backscatter refers to the phenomenon in which radiation or waves are scattered backward, opposite to the direction of the incident beam. This occurs when the incident radiation encounters a target or...

backscattering coefficient, b

Fraction of light counter propagating collinear with the incident source. Processes considering backscattering are Raman, Brillouin, Rayleigh and Mie.

backstreaming

The term used in reference to vacuum systems using oil and diffusion pumps, describes the migration of pump fluids and their decomposition products into the vacuum chamber.

backward-wave oscillator

An amplifying device with a wide tuning range in which an electron gun sends a beam of electrons into a slow-wave structure. The electron beam and the electromagnetic wave move in opposite directions...

bacteriorhodopsin

A light-harvesting protein found in the purple membrane of a micro-organism called Halobacterium halobium. The protein undergoes a photocycle that involves several binary photochemical reactions that...

bakeout

The elimination of gases from the surfaces of a vacuum system by heating the surfaces when the pumping phase is occurring.

ballistic camera

A camera that uses multiple exposures to record the trajectory of an ordnance from a ground-level position.

balloon-borne astronomical system

Any instrument or system carried by a balloon to the upper atmosphere to measure and record atmospheric information, such as radiation observations, while reducing atmospheric interference.

band-elimination filter

A filter that suppresses a given range of frequencies, transmitting only those above and below that band. Also called bandstop filter.

band-to-band photoluminescence

The emission of a photon by the return of an excited carrier from the conduction band to the valence band of a semiconductor along a radiative recombination path. The resulting photoluminescence...

bandgap

In semiconductor physics, the term bandgap refers to the energy range in a material where no electronic states are allowed. It represents the energy difference between the valence band, which is the...

bandpass filter

A filter with a transmission that is high for a particular band of frequencies, but that falls to low values above and below this band.

bandstop filter -> band-elimination filter

A filter that suppresses a given range of frequencies, transmitting only those above and below that band. Also called bandstop filter.

bandwidth

The range of frequencies over which a particular instrument is designed to function within specified limits. See also fiber bandwidth.

bandwidth-limited operation

In fiber optics, the limitation on performance imposed by the system bandwidth rather than the amplitude of the signal.

barcode scanner

An optical scanning device designed to read information printed in the form of bars of different size by detection and processing of the varying reflectivity of light in the barcode.

Bardeen-Cooper-Schrieffer theory -> BCS theory

Bardeen-Cooper-Schrieffer theory of superconductivity, based on the notion that electrons with opposite momentum and spin are paired as a result of forces arising from lattice vibrations. The theory...

barium fluoride

A relatively hard crystal, highly resistant to excessive energy radiation, that is frequently used for optical windows, prisms and lenses transmitting from the vacuum UV into the IR.

Barlow lens

A negative lens used to increase the effective focal length of a telescope objective.

barrel distortion

The negative distortion that causes a square grid pattern to be imaged as barrel-shaped.

barrier layer

In the fabrication of an optical fiber, a layer that can be used to create a boundary against OH-ion diffusion into the core.

baryta -> glass barium

A type of glass containing barium oxide, which is added to increase the refractive index while maintaining a relatively low dispersion.

base-altitude ratio

In aerial photography, the ratio derived from a stereoscopic pair of photographs that represents the air-base length divided by the flight altitude.

baseband

The simplest method of transmission on a local area network. The entire bandwidth of the cable is used to transmit a single unmodulated digital signal. Baseband transmission is capable of...

baseband response function -> transfer function

The complex function, H(f), equal to the ratio of the output to input of the device as a function of frequency. The amplitude and phase responses are, respectively, the magnitude of H(f) and the...

baud

A unit of speed of transmission or receipt of a signal, roughly equal to bits per second; common baud rates are 300, 1200, 2400, 4800 and 9600.

Baume scale

The scale for floating hydrometers used to measure the specific gravity of a polishing suspension. The depth of immersion is a linear function of the inverse of the density. The Baume scale is linear...

bay

In optical character recognition, a feature at the boundary of a character.

BBAR

broadband antireflection

BCS theory

beacon

A device, either visual or electronic, that emits signals to identify set positions for use in the navigation of aircraft and ships along flight paths and channels, or as a warning against entering a...

beaconage

A system of beacons used in navigation.

beam

1. A bundle of light rays that may be parallel, converging or diverging. 2. A concentrated, unidirectional stream of particles. 3. A concentrated, unidirectional flow of electromagnetic waves.

beam attenuator

A device designed to decrease flux density or power per unit area of a light beam through absorption and scattering of the beam.

beam candlepower

With relation to the equivalent beam candlepower of a searchlight, the candlepower of a bare source that would produce the same illumination at the respective point if located the same distance away.

beam converter

A device used to alter the shape of or energy distribution within a beam of radiation.

beam deflection tube

An electron-beam tube in which the current to an output electrode is regulated by the transverse motion of the tube's electron beam.

beam diameter

1. Calculated distance between two exactly opposed points on a beam at a chosen fraction of peak power (typically 1/e2). 2. The diameter of a circular aperture that will pass a specified percentage...

Photonics DictionaryB