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Definitions: D

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D*

A value used to designate the relative sensitivity of a detector. The higher the D* value, the better the detector.

D-star -> D*

A value used to designate the relative sensitivity of a detector. The higher the D* value, the better the detector.

Dall-Kirkham telescope

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

Dammann grating

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...

damped least squares

An organizational method used in optical design computer programs. The technique produces one number (merit function) to measure the state of correction of an optical system. This number, which is...

damping

Continuous conversion of oscillatory energy into heat, relative to time or distance.

dark adaptation

The ability of the human eye to adjust itself to low levels of illumination.

dark beam

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

dark box

A lightproof box used for storing photosensitive materials.

dark current

The current that flows in a photodetector when there is no optical radiation incident on the detector and operating voltages are applied.

dark current density

Dark current density refers to the electric current that flows through a semiconductor device in the absence of any external illumination. It is primarily caused by thermal generation of charge...

dark decay

The decay of an electrostatic charge image resulting from long exposure to the dark.

dark discharge

In a gas, an electrical discharge that has no luminance.

dark fiber

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

dark frame

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...

dark mirror

A multilayer coating that manifests both a low radiant reflectance and radiant absorption.

dark noise

The noise produced in a photodetector when the photocathode is shielded from all external optical radiation and operating voltages are applied.

dark operate mode

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.

dark signal -> dark current

The current that flows in a photodetector when there is no optical radiation incident on the detector and operating voltages are applied.

dark space

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

dark-field condenser

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...

dark-field disc

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

dark-field illumination

The transmission of light by a condenser to observe either very small particles or very fine lines with a microscope.

dark-field microscopy

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...

dark-field photomicrography

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...

dark-line spectrum

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

darkening

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

darkroom

A room that is light-tight, permitting total darkness or illumination with a safelight when working with photosensitive materials.

data acquisition software

Data acquisition software is a type of application or system designed to capture, process, and store data from various sensors, instruments, or devices in real-time or near-real-time. It facilitates...

data acquisition systems

A data acquisition (DAQ) system is a combination of hardware and software used to collect, process, and analyze data from physical phenomena or processes. data acquisition system suppliers...

data analysis display

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

data analysis software

Data analysis software is a category of software tools used for the systematic examination of data sets to uncover patterns, trends, relationships, and insights. It supports a range of analytical...

data bus

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

data compression

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.

data cube

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...

data link

The communications network between nodes of a data transmission system.

daylight lamp

An incandescent or fluorescent lamp whose emittance spectrum resembles that of daylight.

dBm

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

DC blocking -> zero-order filtering

The removal of the zero-order component of the Fourier spectrum distribution of an object with a small, opaque absorber or reflector in the Fourier plane, to produce images that appear bright on a...

de Broglie wavelength

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...

deblocking

The removal of optical elements from a block.

Debot effect

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

Debye effect

The selective absorption of electromagnetic waves by a liquid made up of molecules with permanent dipole movement.

Debye-Scherrer-Hull method -> x-ray analysis

The series of processes used to identify and evaluate crystal structure by using crystalline solids to diffract x-rays. In the Laue method, radiation of a wide range of wavelengths is transmitted by...

Debye-Sears ultrasonic cell

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...

decentering

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...

decentration

In a single element, any lack of coincidence between the optical and the mechanical axes. In a lens system, any lack of coincidence of optical axes of the lens elements that make up that system.

decentration aberration

An aberration occurring in a lens system when one or more of the centers of curvature of the optical surfaces do not coincide with the system's axis.

deci

Sl prefix meaning one tenth, 10-1.

decibel

The standard unit used to express gain or loss and relative power levels. The decibel (dB) = 10 log (P2/P1).

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