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46 terms

Photonics Dictionary: B

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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.

biprism interference

Light interference fringes that can be viewed on a screen near a biprism.

black surface enclosure

An enclosure whose walls are coated to absorb completely all radiation striking them.

back-coated mirror

A glass substrate that has its rear surface coated with a reflective coating. Also known as a back-surface mirror.

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...

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.

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.

bandwidth-limited operation

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

beam divider -> beamsplitter

A beamsplitter is an optical device for dividing a beam into two or more separate beams. A simple beamsplitter may be a very thin sheet of glass inserted in the beam at an angle to divert a portion...

beam-addressable technology

The application of reversible writing with a laser beam on particular storage materials. In one method, an amorphous film is heated and then crystallized for writing. Bubble writing involves the...

beamsplitter

beauty defect

A defect on or in an optical element that does not appreciably impair the function of the surface.

Becke apertometer

Device used to measure the numerical aperture of a microscope, composed of a 14-mm-thick glass block with numerical aperture gradations carved onto its lower surface.

bench -> optical bench

A support for optical parts comprising a solid bed that permits precise longitudinal movement of one component relative to the others, and a number of sliders equipped with holders for lenses, lamps,...

bending of light

1. That action occurring when light passes through an optical interface at other than normal incidence, i.e., refraction. 2. The curving of a path of light that passes close by a massive object, due...

Bertrand lens

A small convergent lens, located between the objective and eyepiece of a microscope, that focuses an image of the upper focal plane of the objective in the focal plane of the eyepiece. It is commonly...

bias buildup

Degradation factor in coherent light systems where the amplitude of the recorded signal is decreased as the number of object points is increased, resulting in poor noise performance.

bifurcated fiber

A branched fiber optic lightguide that performs both receiving and transmitting functions.

bilinear interpolation

It is often necessary to estimate the value of what a pixel would be between neighboring pixels. This is accomplished by interpolating (or inserting) the value of a pixel between neighboring pixels....

Billet's split lens

An experimental lens used to produce interference fringes. A positive lens is cut into halves along its center, and the halves are separated. This produces a double image of a slit source set...

biprism

A piece of glass polished flat on one side, with a pair of polished faces that form an angle close to 180° on the other side, the dividing edge running down the middle of the plate. It is used...

bistable display

A matrix-controlled display that has information storage at the display surface, and requires that an element be addressed only once to assure that it is on or off.

bitoric lens

A lens, both surfaces of which are ground and polished into a toric or cylindrical form.

blackbody

An ideal body that completely absorbs all radiant energy striking it and, therefore, appears perfectly black at all wavelengths. The radiation emitted by such a body when heated is referred to as...

blackbody source

A blackbody source, often simply referred to as a blackbody, is a theoretical or practical physical object that absorbs all electromagnetic radiation incident upon it and emits radiation in a...

blacking -> optical blacking

A light absorbing material applied to ground optical surfaces during the process of making that surface non reflective. Such material should have a refractive index as high as that of the underlying...

blaze

1. A plane that forms one side of the groove ruled on a diffraction grating. 2. To form the individual grooves of a grating with flat smooth faces, inclined to the surface by an angle known as the...

blaze height

Blaze height typically refers to a parameter in the context of diffraction gratings, which are optical devices consisting of a series of closely spaced parallel grooves or slits. The blaze height is...

blur circle

A blur circle refers to the out-of-focus region in an image captured by an optical system. When an object in a scene is not in perfect focus, its image is spread out into a circular shape on the...

Bohr's frequency relation

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...

Bose-Einstein condensate

A Bose-Einstein condensate (BEC) is a state of matter that forms at temperatures close to absolute zero. It is named after Satyendra Nath Bose and Albert Einstein, who independently predicted the...

Brace prism

A compound prism composed of two 30° prisms, one of which is partially coated with a suitable opaque metal of high reflecting power. The prisms are cemented with Canada balsam so that the coated...

Bragg method of crystal analysis

A technique in which a beam of x-rays is directed against a crystal, the atoms of which, because of their lattice arrangement, reflect the ray in the same way as a series of plane surfaces. If the...

Brewster's angle

For light incident on a plane boundary between two regions having different refractive indices, the angle of incidence at which the reflectance is zero for light that has its electrical field vector...

Brewster's fringes

The fringes used in the Jamin interferometer and produced by light that has been internally and externally reflected by two plane-parallel plates, inclined toward each other at a small angle.

brightfield

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...

brightness -> luminance

Luminous flux emitted from a surface per unit solid angle per unit of area, projected onto a plane normal to the direction of propagation. Also known as brightness and luminous sterance.

brightness meter

An instrument for measuring the brightness (luminance) of a scene. It may be a spot meter, covering an area of a degree or less, or an averaging meter, covering a broad area of the scene. Brightness...

bring-in

The final correction of a polished surface or of an angle to the specified precision.

broadband dielectric mirrors

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...

bubble memory -> magnetic bubble film

An amorphous film in which cylindrical bubbles of reverse magnetization can be formed to follow circuit paths usually made by depositing magnetic metal strips on the film surface. It is used in...

bubble writing -> beam-addressable technology

The application of reversible writing with a laser beam on particular storage materials. In one method, an amorphous film is heated and then crystallized for writing. Bubble writing involves the...

burn

A surface imperfection caused by a polisher running dry too long. It occurs with felt or plastic polishers, and may appear as a reddish brown.

Photonics DictionaryB