Photonics Dictionary: D

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

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

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...

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...

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

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

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.

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

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

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

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...

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

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

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.

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

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

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.

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

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 communications network between nodes of a data transmission system.

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

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