Photonics Dictionary: D

The progressive defocusing of a cathode-ray tube display image that occurs when the deflected electron beam impinges on the cathode-ray tube screen at a slant.

A spatial light modulator consisting of a metallized polymer film stretched over an array of metal-oxide semiconductor field-effect transistors (MOSFETs). Each mirror element in the film can be...

Any of the constants that relate the tendency of the director to remain parallel to restoring torques throughout the media. The three constants of importance in liquid crystal displays are: splay --...

The exact mathematical description of the interactions of matter and intense electromagnetic fields, such as those that occur when laser sources are used to excite flame gases for spectroscopic...

The range of image distances that corresponds to the range of object distances covered by the depth of field.

In a camera, the focusing of an image on the screen located at the camera's film plane. Once the image is in complete focus, the recording medium is inserted in place of the screen.

A composite derived from aluminum alloy powder and silicon carbide, used as an optical substrate in air- and spacecraft applications. It is as light as aluminum but exhibits greater strength and...

A mathematical transformation used in image and video compression that changes two-dimensional representation of data into data defined by the frequency content. Adapted in JPEG and MPEG standards.

All formulas that present the index of refraction as a function of a wavelength of electromagnetic radiation. Also called dispersion equation, Cauchy formula, Hartmann formula.

A mass spectrometer utilizing both radial electrostatic and magnetic field analyzers to improve the focusing and increase resolution.

A mode of laser printing in which each pixel is printed four times, providing sharper lines and a continuous tone from one-quarter the amount of image data, compared with single-raster output.

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 precision-engineered microminiature light source that is safe for darkroom use, yet emits a beam of light bright enough to read by.

A lightproof box used for storing photosensitive materials.

Unused fiber; fiber that has been installed but reserved for future use. Carrying no light.

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...

An operate mode in which the sensor is programmed to perform a task such as generating output when the light level falls below a certain threshold.

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 disc contained within an electronic cell counter for regulating light transmission.

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 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...

Decibels referenced to one milliwatt; often used to specify power ratings for semiconductor diode lasers.

A structural method of optical character recognition, used where the input media are variable, as in hand-written or multifont documents. A series of questions (such as "Does the character contain a...

Deep learning is a subset of machine learning that involves the use of artificial neural networks to model and solve complex problems. The term "deep" in deep learning refers to the use of deep...

Deep ultraviolet (DUV or deep-UV) refers to a specific range of ultraviolet light with shorter wavelengths than those in the UV-A and UV-B regions. The exact wavelength range considered as DUV can...

A CCD device for sensing longer wavelengths, such as NIR and IR, that has a deeper depletion region than would be necessary for sensing in the visible wavelength range. Because the depth of charge...

A chart, either printed on paper or prepared photographically on glass plates or film, that consists of 3-bar resolution test objects, sine-wave test objects for modulation transfer function...

Any bending of a wave of radiation away from its expected path, as, for example, by diffraction or by a magnetic field.

For an optical table, the amount of displacement that occurs when a heavy load is placed or moved on the surface. To measure deflection under static load, a 113-kg (250 lb) weight is placed in the...

A device used to delay transmission of a signal for functions such as memory loops, sequential processing or built-in testing. The delay can be achieved by coiling long lengths of coaxial cable or...

A compact, folded version of a Dove prism, made of high-index glass with a silvered base and used for image rotation.

1. An instrument used to measure the opacity or density of dyes, pigments or dispersed particles that form an image in or on a medium, such as a photographic film. 2. A device used to measure the...

A critical image parameter in applications where object position may change dynamically relative to the imager; this is a sensitive function of the system's preclosed loop (initial) focal range and...

The distance, on either side of the object plane focused on, through which satisfactory image definition can be obtained. For the special case of an imaging system with lens axis perpindicular to the...

The direct appreciation of the distance between a given object and the observer, or between the front and back of a solid object. Real depth perception is achieved by the retinal disparity formed by...

The ray refracted by a sphere of transparent material that travels back as closely as possible to the original path formed by the incident ray.

Design and engineering consulting services refer to professional services provided by specialized firms or individuals to assist clients in various aspects of product development, system design, or...

Observed electroluminescence of zinc sulfide phosphors when excited by an electric field. This effect is the basis for the alternating-current phosphor panel technology.

The interaction of superimposed light from two separate sources that results in a combined intensity that is less than the sum of their individual intensities before they were superimposed.

1. A device designed to convert the energy of incident radiation into another form for the determination of the presence of the radiation. The device may function by electrical, photographic or...

A detector array refers to a collection of individual detector elements arranged in a two-dimensional grid or matrix format. Each element within the array is capable of detecting electromagnetic...

A detector-Dewar assembly typically refers to a combination of a detector and a Dewar flask used in scientific instruments, particularly in the field of infrared spectroscopy or other applications...

A discharge lamp filled with deuterium to produce high-intensity ultraviolet radiation for use in spectroscopic analysis.

The process by which a vitreous or amorphous substance forms a crystal structure at a specified temperature.