Photonics Dictionary: D

A telescope similar to the customary Cassegrain telescope, but having a primary mirror that is ellipsoidal and a secondary that is spherical.

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.

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...

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

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...

The condition in which two or more energy states are identical.

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...

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.

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.

The square of the ratio of the measured detectivity to the theoretical maximum detectivity.

A measure of the sensitivity of a detector; the reciprocal of noise equivalent power (NEP). See D*.

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...

In optical communication systems, operations in which the amplitude of the pulses, as opposed to their width, determines the distance between repeaters.

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 device in which the functions of optical detector and emitter are combined.

A type of pyroelectric detector with favorable qualities of linearity, sensitivity and spectral responsivity used in FTIR detectors.

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

Able to rotate the plane of polarization of a transmitted, plane-polarized light beam clockwise as seen by a viewer looking in the same direction as the traveling light. Also called dextrorotary; the...

An airspaced achromatic doublet telescope objective.

A telescope that corrects dispersion and spherical aberration through the use of one or more lenses, usually smaller than the objective lens, that are positioned at a distance from the objective lens.

A shutter consisting of a ring of interweaving blades that open outward and allow light to pass when they are pivoted at their outer edges.

In an optical rangefinder, the system of wedges that rotate in opposite directions to aid in the detection of deviation in the image axis.

A shallow, fine-pitch diffraction grating having a precise dielectric overcoating that experimentally has absorbed wavelength-specific incident light that is polarized in the P-plane.

Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast microscopy, is an optical imaging technique used in microscopy to enhance the contrast of transparent...

A device that produces an interferogram that can be directly related to the temperature gradient and thereby provides a direct measure of the convective heat transfer coefficients.

The variation in attenuation among the propagating modes of an optical fiber.

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.

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

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.

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

A color filter that is designed to gradually increase or decrease its absorption with wavelength.

A filter purposely made to be placed before a lens to render the image rather unclear.

A linear computation or algorithm performed on a selected series in the form of an input signal that produces a new series as output. The computational device may be a specifically designed...

A pixel-based computer graphics system that simulates the tools of an artist.

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

An instrument used to measure expansion of solids, liquids and gases.

The logarithmic method of determining emulsion speeds developed by the German standards organization, Deutscher Normenausschuss, in which the speed of the emulsion is doubled for each increase of...

A diode-pumped solid-state laser (DPSSL) is a type of laser system that uses semiconductor diode lasers to pump energy into a solid gain medium, resulting in the generation of coherent light. This...

The adjustment of the eyepiece of an instrument to provide accommodation for the eyesight differences of individual observers. The axial distance through which the eyepiece must be moved, to provide...

A scale located on the eyepiece focusing screw and used to measure the amount of defocusing of the eyepiece in diopters. The reciprocal of the image distance in meters is a measure of the amount of...

A unit of optical measurement that expresses the refractive power of a lens or prism. In a lens or lens system, it is the reciprocal of the focal length in meters. For example, if a lens has a focal...

A telescopic system having an eyepiece, a reticle and an objective. The instrument measures wavefront power in diopters.

An optical system that uses refraction to form an image.

In a fiber optic transmission system, the conversion of received optical pulses directly to an electrical signal.

Also called DLIP, a high-speed, high-resolution processing technique that uses high-power, pulsed laser systems to directly ablate micro- and nanoperiodic structures with different features on large...

A write-once optical disc storage system in which the optical head reads continuously while writing to check the accuracy of the stored data. Data recorded erroneously are then rewritten at another...