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7,367 terms

Photonics Dictionary

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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.

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.

backsided-illuminated sensor

A backside-illuminated (BSI) sensor is an image sensor technology where the light-sensitive elements (typically pixels) are positioned on the opposite side of the sensor substrate from where light...

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...

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...

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 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 (optical adapter)

An optical adapter typically refers to a device or component used in optical systems to facilitate connections between different types of optical fibers, connectors, or interfaces. Here are a few...

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.

basal plane

A plane in a crystal that lies parallel to the principal plane of symmetry.

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...

baselength

The distance between pupil centers in a two-pupil system, measured perpendicularly to the optic axis.

baseline

The smallest amount of photon energy to pass a detector window and be counted.

basic roughness

The roughness profile shape from which light scattering is expected to occur.

bathymetric lidar

Bathymetric lidar is a remote sensing technique used to measure the depth of water bodies and map underwater terrain features. It employs lidar (Light Detection and Ranging) technology, which uses...

bathymetric map

A surveying map representing measurement of depth, particularly that of the ocean.

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.

bayonet coupling

A coupling mechanism designed to quickly lock a connector into an adaptor or a lens into a lens mount. Typically coupling is accomplished by less than a quarter turn of the component being mounted.

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