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412 terms

Photonics Dictionary: C

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calligraphic imager -> stroke pattern

The pattern formed by a character generation cathode-ray tube system, in which the characters are composed of a sequence of line segments (strokes) generated by the electron beam motion with time...

calcium tungstate

White, tetragonal crystals used in the production of luminous coatings.

Cassegrain lens system

A two-mirror lens design used in astronomical telescopes, the primary being a parabola, the secondary a smaller hyperbola. The image formed is free of spherical aberration and color and is located...

catacaustic

A caustic formed by reflection.

catadioptric imaging system

A system that uses both reflection and refraction to achieve its focal power. While the relative powers of the lenses and mirrors vary from system to system, the use of the reflective surfaces to...

catastrophic optical damage

The darkening of the laser facet of a semiconductor laser diode. It can be prevented by placing the component in a hermetically sealed enclosure.

cathode stream

Also known as cathode rays. Formerly, this term described a stream of electrons emitted from the cathode of a gas-discharge tube during its bombardment by positive ions. It also describes any stream...

catoptric system

An optical system in which the only image-forming elements are curved-surface mirrors; e.g., a Cassegrain lens system.

caustic

A surface that envelops a bundle of rays or bundle of normals to the wave surface. It may be observed as a hollow, luminous cusp in a turbid medium.

centerburst

In an interferogram, an intense portion of the recording that corresponds in size to the amount of infrared radiation incident on the detector.

centered lens system

A lens system in which the centers of curvature of all surfaces fall on a common axis.

central obstruction

In a reflecting telescope, the obstruction of the primary mirror by a secondary mirror which blocks a small amount of the light reflected by the primary mirror and introduces additional diffraction.

channel substrate planar growth

The creation of a diode laser structure by liquid-phase epitaxy over a grooved substrate.

character read-out system

A photoelectrically controlled, alphanumeric reading device that converts characters to audible or sorting signals which can be fed to a computer, electric typewriter, tapepunch or other machine.

characteristic angle

The angle at which a given mode propagates down an optical fiber.

characteristic curve

A graph used in photography to portray the increase of a film's density as its time of exposure increases.

cholesteric phase

The state of a liquid crystal in which the molecules are arranged in layers with their long axes in the plane of each layer. The alignment in each layer is parallel and the alignment in adjacent...

Christiansen effect

The monochromatic transparency effect produced by the immersion of a finely powdered substance (e.g., glass or quartz) into a liquid with a similar refractive index.

Christiansen-effect filter

A transparent powdered solid immersed in a liquid or plastic of similar refractive index but widely different dispersion; used to isolate narrow spectral regions.

CIE system

Methodology for specifying color based on the CIE sources, observers, and coordinate system.

circle of least confusion

Best point of focus for an image in a beam of light at the smallest cross section of the beam.

cladding mode stripper

A mechanism or device, especially a coating with a refractive index equal to or slightly greater than that of an optical fiber's cladding, that removes modes propagating through the cladding by...

clear eye distance

In a visual optical system, the axial distance from the last mechanical surface of the eyepiece to the exit pupil.

closed-circuit television system

A television system that does not broadcast television signals but transmits them over a closed circuit.

CMOS quantitative polymerase chain reaction system

This type of miniaturized system, referred to as CMOS qPCR, combines microfluidic technology with an ultralow-light CMOS bio-optical sensor with LEDs as the optical excitation source to achieve...

coelostat

A plane mirror mounted on a polar axis that lies parallel to the plane of the mirror. When the mirror is rotated once in 48 hours, celestial objects can be made to appear stationary and are...

coherent anti-Stokes Raman scattering

A technique whereby two laser beams, one at an excitation wavelength and the second at a wavelength that produces Stokes Raman scattering, interact coherently in a sample, producing a strong...

color aging test

A test used to measure the degree of fading of different colored materials, especially those involving organic dyes, which tend to fade when exposed to bright sunlight, to a damp atmosphere or to...

color monitoring instrument

An instrument providing a continuous measure of color.

color perception test equipment

Equipment for testing an observer's color vision. Some tests require the identification or ordering of colored samples. The commercially available examples include: the Ishihara plates, on which...

common optoelectronics laser detection system

A laser warning and countermeasure system containing a sensor that indicates the direction of a laser beam, and analytical instruments to determine pulse code, repetition frequency and wavelength.

computer graphics workstation

The physical area containing an assembly of computer graphics equipment for presenting generated images and allowing interaction between the user and the computer.

computer-output microfilm system

A camera system capable of producing microfilm copies of computerized data presented on a screen.

conjugate autofocus system

A system that determines whether an image is in or out of focus by means of a source of illumination at the conjugate focal point, which reflects off the target; the return beam is mediated by masks...

const

constant

constant angle fringes -> Haidinger fringes

Also known as constant angle or constant deviation fringes. The interference fringes observed with dense flat plates near normal incidence. The fringes of the Fabry-Perot interferometer are Haidinger...

constant deviation

That property of certain optical devices, e.g., a penta prism, that maintains the angular relationship between the entering and the emerging rays traversing the system regardless of the orientation...

constant deviation fringes -> Haidinger fringes

constant linear velocity

Method of disk rotation used for optical disk drives, in which the spindle motor decreases the speed of the disk's rotation as the head moves from the inner tracks to the outer, so that the radial...

constant luminance encoder

A device used in broadcast CCD cameras to improve definition in heavily saturated colors by band-limiting the color difference signals after gamma correction.

constant variant enhancement

Technique that uses high-pass filtering to reduce the local average to zero for all regions of the picture and then applies a gain factor equal to the reciprocal of the local standard deviation to...

constrigence

Reciprocal of the dispersive power of an optical material. See Abbe constant.

contrast

The apparent difference in brightness between light and dark areas of an image. For a light target against a dark background, contrast is computed as follows: where Lt is the luminance of the...

contrast control

With respect to television, a potentiometer that allows variation of the intensity of the different elements of an image and that can be used to accentuate the highlights and shadows in an image. In...

contrast filter

A filter designed to improve contrast in an imaging system. For visual and black and white photosystems, a yellow filter is used.

contrast improvement

One area of image enhancement, accomplished by spatial filtering schemes, that usually involves attenuation of phase changes in the complex amplitude over a limited region of the Fourier spectrum of...

contrast threshold

That contrast level that exists between two areas whose difference in brightness is just perceivable.

contrast transfer function -> modulation transfer function

Also called sine wave response and contrast transfer function. The modulation transfer function is the ratio of the modulation in the image to the modulation in the object as a function of frequency...

Cotton-Mouton constant

Relative to the Cotton-Mouton effect, the magnetic birefringence constant that, when multiplied by pathlength and the square of the magnetic field strength, yields the phase difference between the...

covalent crystal

A crystal formed by covalent bonds that are generally highly directional by nature. The electric characteristics of these crystals classify them as semiconductors.

Photonics DictionaryC