Photonics Dictionary: B

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.

A photovoltaic cell designed so that light travels through the front electrode and a semiconductor before it comes to the barrier layer.

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

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

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

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

Activity of a radionuclide having one spontaneous nuclear transition per second.

The intensification of a latent image, because of exposure to light to which the emulsion is otherwise insensitive.

In optics, a collapsible structure situated between the lens and film of a camera to allow variation of the distance between them while preventing surrounding light from exposing the film.

Two formulas used in diffractometer analysis, the first giving the individual diffraction patterns of each aperture, the second representing the constant of the degree of an incoherent circular...

A chamfer ground on the edge of a lens or prism. Bevels are used to prevent chipping or to achieve a mechanical fit.

The actual width of a bevel rather than its width projected along the lens aperture.

The level of the television picture signal that corresponds to the maximum limit of black peaks.

The light wavelength for which the direction of reflectance from the groove face is identical to the angle of diffraction for a specified angle of incidence.

The law given by the formula: that is, the frequency of radiation emitted or absorbed by a system when E2 and E1 are the energies of the states among which transition takes place, and h is...

The illumination generally used in microscopy, whereby the specimen appears dark against a light background.

An optical image having a brightly lit background.

Brightfield refers to a type of microscopy and imaging technique in which the specimen is illuminated with a white light source, and the image is observed or captured against a bright background. In...

Broadband dielectric mirrors, also known as broadband mirrors, are optical coatings designed to efficiently reflect or transmit light over a broad range of wavelengths. These mirrors are constructed...

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...

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

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...

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...

An opaque shielding device designed to reduce the effect of stray light on an optical system.

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

A two-mirror corrector for a parabolic primary mirror that provides anastigmatic performance for large astronomical telescopes.

A wide-field camera based on the classic Schmidt optical system used to photograph Earth-orbiting satellites.

In a laser, the series resistance necessary for a stable electrical discharge.

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

The measured wavelength of the most distinct edge of a spectral band.

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...

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...

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.

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.

A crystalline material used in piezoelectric devices.

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

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

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...

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...

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.