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163 terms

Photonics Dictionary: D

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digital video compression

A step-by-step method of reducing the amount of data in a digital video signal to transmit or store a high-quality image. The digitized picture is analyzed, and fine detail and redundant pixels,...

digital-to-analog converter

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

digitizer

A device that samples and quantizes a signal in digital form for storage in memory.

DIN system

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...

diode laser -> diode laser

A diode laser is a type of laser that uses a semiconductor diode as the active medium to generate coherent light. Semiconductor diodes are electronic devices that conduct electricity primarily in one...

diode laser

diode-pumped solid-state laser

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...

diopter movement

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...

diopter scale

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...

diopter

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...

dioptric system

An optical system that uses refraction to form an image.

direct viewfinder

A viewfinder whose optical system forms a direct image of a subject, as opposed to those systems that use reflectance in the image formation.

direct-view storage tube

A cathode-ray tube in which secondary emission electrons form a display of high intensity.

directed energy

Directed energy refers to a type of energy that is emitted and transferred in a controlled direction. The term is often associated with military and technological applications where energy, typically...

directional reflectance

Reflectance in a specified direction, for a specified direction of incident illumination.

disc

A piece of glass that eventually becomes the bifocal segment as it appears prior to being fused to the blank.

disc colorimeter

A colorimeter using a spinning disc made of different colored sections for colorimetric analysis.

dislocation

The region of distorted atom configuration formed between the displaced and normal areas in a crystal when part of the crystal is displaced tangentially.

dispersion

Dispersion refers to the phenomenon where different wavelengths (colors) of light travel at different speeds when passing through a medium. This variation in the speed of light for different colors...

dispersion-shifted fiber

A dispersion-shifted fiber (DSF) refers to a type of optical fiber designed to minimize the effects of chromatic dispersion, which is the phenomenon where different wavelengths of light travel at...

dispersive correlation spectrometer -> mask spectrometer

Instrument that uses absorption spectroscopy to detect gases in planetary atmospheres. Dispersed incoming radiation is transmitted to one or more sampling elements, or masks, before reaching the...

dispersive lens -> diverging lens

A diverging lens is a type of lens that causes parallel rays of light to spread out or diverge. It is thinner in the center than at the edges and is commonly referred to as a concave lens. The most...

display console

A visual display used with a computer to give access to the many elements of data as an array of points. With the display console, an operator may check information in the computer and change it if...

display primaries -> receiver primaries

Also known as display primaries. Colors formed by a television receiver that are of constant chromaticity and variable luminance, and that, mixed in certain proportions, form other colors. Red, green...

distortion

A general term referring to the situation in which an image is not a true-to-scale reproduction of an object. The term also is used to connote the temporal alteration of the signal's waveform shape....

distortion-limited operation

The limitation on performance imposed by the distortion of a received signal rather than its amplitude or power.

distributed feedback laser

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...

distribution temperature

Temperature of the blackbody having a spectral power distribution approximately proportional to the test source at all wavelengths; it follows that the two have the same chromaticity.

dithering

In image processing, modifying the dot that forms the image in order to simulate a series of gray tones.

divergent lens -> diverging lens

diverging lens

divided circle spectrometer

A spectroscope having a divided circle and a means for the rapid reversal of prisms for the measurement of refractive index of the prism for a specific wavelength.

DMD

deformable membrane device

Dogmar/Aviar lens

A general-purpose lens, also known as the Celor lens, used widely in photography and commercial processing; it has the form of a triplet with a split flint element.

doma

A primitive crystal possessing two plane surfaces that form a dihedral angle bisected by another plane surface.

dome -> optical instrument dome

A dome-shaped structure used for some optical instruments in place of a flat window. The transparent material should be of good quality and the hemispherical surfaces should be concentric.

donpisha

A type of asynchronous shutter device that is used particularly in CCD sensor applications to capture an image of a high-speed subject with no time delay. The word donpisha is taken from the Japanese...

doping

In the context of materials science and semiconductor physics, doping refers to the intentional introduction of impurities into a semiconductor material in order to alter its electrical properties....

Doppler broadening

The spreading of potentially equal radiation frequencies that results in broadening of the spectral line. This effect is brought about when radiating atoms, molecules or nuclei have different...

Doppler velocimeter -> laser Doppler velocimeter

Device which determines particle velocity through the measurement of scattered interference of a beam pair from a single source. The measured light is Doppler shifted which provides information...

dot matrix display

A display format consisting of small light-emitting elements arranged as a two-dimensional array. Various elements are energized to depict a character. The typical matrix is 5 x 7 dots.

double refraction

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...

double vision

A defect of a binocular instrument causing two images to be seen separately instead of being fused. It is caused when the optical axes of the two telescopes are not parallel. In minor cases, the eyes...

double-clad fiber

Double-clad fiber (DCF) is a specialized optical fiber that features two concentric cladding layers surrounding a core. The design of double-clad fibers allows them to be used in various...

double-discharge laser

A type of transversely excited laser with a uniform arc-free discharge of large cross-sectional area that can be scaled to very large systems.

double-exposure holography

The formation of an interferogram by means of two holograms on the same recording medium, often used for determining small changes in an object. One hologram produces a primary image that constitutes...

double-image prism

A prism block that, when used with a lens, is capable of forming two images of one object.

double-pulsed holographic interferometry

Interferometric measurement of the interference pattern recorded when a complex object is illuminated by two laser pulses that interfere and form the pattern to be evaluated.

Dove prism

A form of prism invented by H.W. Dove. It resembles half of a common right-angle prism in which a ray entering parallel to the hypotenuse face is reflected internally at that face and emerges...

DRA

discontinuously reinforced aluminum

Photonics DictionaryD