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Definitions: B

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b integral
Calculates the exponential growth of the least stable spatial frequency in a laser beam, and is the numerical equivalent of the nonlinear phase shift along the laser system's optical axis.
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.
back-coated mirror
A glass substrate that has its rear surface coated with a reflective coating. Also known as a back-surface mirror.
back-illuminated CCD
A CCD that has been reduced in thickness by etching so that light passes through the back layers of the CCD. This type of CCD typically has higher sensitivity, especially to blue light, and higher...
back-surface mirror -> back-coated mirror
A glass substrate that has its rear surface coated with a reflective coating. Also known as a back-surface mirror.
back-wall photovoltaic cell
A photovoltaic cell designed so that light travels through the front electrode and a semiconductor before it comes to the barrier layer.
background luminance
The intensity of the light in the scene behind an object being viewed.
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.
backlit
Refers to a display or screen that is illuminated from behind; the light is transmitted as opposed to reflected.
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...
baffle
An opaque shielding device designed to reduce the effect of stray light on an optical system.
bakeout
The elimination of gases from the surfaces of a vacuum system by heating the surfaces when the pumping phase is occurring.
Baker corrector
A two-mirror corrector for a parabolic primary mirror that provides anastigmatic performance for large astronomical telescopes.
Baker-Nunn camera
A wide-field camera based on the classic Schmidt optical system used to photograph Earth-orbiting satellites.
ball lens
A ball lens is a small, spherical optical component typically made of glass or other transparent materials. It is characterized by its spherical shape, with both its front and back surfaces forming...
ballast resistance
In a laser, the series resistance necessary for a stable electrical discharge.
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.
balsam -> Canada balsam
A resin obtained from the balsam fir, Abies balsamea, used as a lens cement.
band head
The measured wavelength of the most distinct edge of a spectral band.
band spectrum
A spectrum that originates from molecules and that is composed of bands which, in turn, consist of many closely spaced lines. Band spectra are used to determine nuclear spin and statistics, and...
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
The range of frequencies that will pass through a filter or other device. Synonymous with passband.
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.
barium titanate
A crystalline material used in piezoelectric devices.
Barlow lens
A negative lens used to increase the effective focal length of a telescope objective.
barrel -> adapter
1. In optics, the housing, usually cylindrical, that contains the lenses and iris diaphragm of a camera. 2. In fiber optics, a device for coupling two connectors.
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.

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