Photonics Dictionary: D

The portion of a glow discharge tube that permits little or no light transmission.

An approach to optical character recognition based on matching the input character against a set of stored prototypes.

A caustic formed by refraction.

As a wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with...

The angle that lies between the direction of an incident light beam and any resulting diffracted beam.

Diffraction efficiency is a measure of how effectively a diffractive optical element (DOE) or diffraction grating directs light into specific diffraction orders or achieves a desired optical effect....

The formation of a fan of light or energy rays in a beam as the beam passes through an extremely narrow aperture.

A spectrograph that uses a diffraction grating as its dispersive element in place of a prism, and yields greater resolving power, more dispersion and a linear spectrum.

A diffraction grating is an optical component consisting of a surface with a periodic structure of equally spaced, parallel grooves or rulings. These rulings act as an array of closely spaced slits...

The property of an optical system whereby only the effects of diffraction determine the quality of the image it produces.

The interference pattern formed by light waves diffracted at the edges of an object as seen on a screen placed in their path.

1. The ring patterns of light that seem to encircle particles in the field of a microscope. 2. See Newton's rings.

Elastic scattering that occurs when inelastic processes eliminate particles from the beam.

In spectroscopy, the parallel bands that vary in lightness and darkness or color, and that are formed when light is diffracted by a sample.

A lens with aberrations corrected to the point that residual wavefront errors are substantially less than one-quarter the wavelength of the energy being acted upon.

Any optical device that utilizes diffraction in an image-forming capability. Familiar diffractive lenses are zone plates, holographic lenses, kinoform lenses and binary optics.

Optical elements that use diffraction to control wavefronts. Diffractive optical elements include diffraction gratings, surface-relief diffractive lenses, holographic optical elements and...

A measurement device used to study the structure of matter using the diffraction of electromagnetic radiation.

The study of the diffraction of beams of a wave by matter to ascertain the structure of the matter.

The process by which the values of one digital image of an object or scene are removed from a second slightly different image of the same object or scene.

A distributed feedback laser (DFB laser) is a type of semiconductor laser diode designed to emit coherent, narrow-bandwidth light with precise control over the wavelength. It achieves this through a...

The separation of unpolarized light into two plane-polarized elements by a doubly refracting crystal. When a crystal, such as calcite, is placed between the eye and a pinhole in a card, two bright...

A transparent crystalline substance that is anisotropic relative to the velocity of light.

In a dual-ring local area network, a node that is connected both to the primary, active ring and also to a secondary ring that provides redundancy in case of cable or system failure.

A package for electronic components that is suited for automated assembly into printed circuit boards. The DIP is characterized by two rows of external connecting terminals or pins, which are...

Diamond turning, also known as diamond machining or diamond cutting, is a precision machining process used to produce high-quality optical surfaces and components with extremely tight tolerances. It...

In image processing, a device that transforms the digital data into an analog video image that can be viewed on a monitor or printed.

A Dammann grating is a type of diffractive optical element (DOE) used to create an array of equally spaced, uniform-intensity spots or beams. It is named after its inventor, Dr. Herbert Dammann. The...

A frame taken to identify electronic noise in a CCD imaging device. A dark frame is recorded without exposing the CCD to any external light by, for example, leaving the shutter of a CCD camera...

A condenser that forms a hollow cone-shaped beam of light with its focal point in the plane of the specimen. If it is used with an objective having a numerical aperture lower than the minimum...

A technique whereby the sample is illuminated by a hollow cone of light larger than the acceptance angle of the objective, so that only scattered light is seen, revealing any irregularities of the...

A photomicrographic recording technique that utilizes dark-field illumination to render an image of an object having a refractive index much like that of the medium holding it. The object may be...

A spectrum having some lines that are darker than others or that contrast against a light, continuous-spectrum background.

The formation of a dark-colored film on a metal surface by chemical activity.

An accurate cathode-ray tube display used to provide visual representation stored in a computer for the interpretation and evaluation of the data.

A system incorporated into fiber optic data communications characterized by several spatially distributed terminals that are served with the same multiplexed signal.

A method of storing digital data using techniques that consume less memory space than basic methods do. See differential pulse code modulation; run end coding; run length coding.

A multidimensional array of values that is commonly used in programming to describe a time series of image data. Each dimension in the data cube represents a new attribute, while the cells of the...

The concept of the de Broglie wavelength exploits the wave-particle duality of quantum physics by associating all matter (of all sizes) with wavelike properties. The de Broglie wavelength states that...

The conversion of an internal latent image into a surface latent image through exposure to infrared radiation. The converse of the Herschel effect.

A device used in ultrasonic imaging to measure the velocity and attenuation of compressional waves in a transparent liquid by virtue of acoustic waves set up in the liquid. The wavefronts serve as a...

1. The grinding or edging of a lens so that the geometrical center and optical center do not coincide. 2. The shifting of an optical element from the system's optical axis, sometimes done on purpose...