Photonics Dictionary: D

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...

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...

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...

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 distortion created because the different frequencies of a signal have different propagation velocities through a medium.

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.

A caustic formed by refraction.

A number that indicates the magnitude of the shift in a solid of positive and negative charges in opposite directions when a voltage is applied across the solid.

A crystal that is characterized by its relatively poor electrical conductance.

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

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...

An optical system that uses refraction to form an image.

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

The end of an optical fiber farthest from the source of illumination.

The near-point distance of the normal eye. The value of 10 in. or 25 cm is normal. This value is used in evaluating the designated magnification of a simple magnifier or eyepiece.

In astronomy, the relation that states that the intensity of a star's visible radiation is inversely proportional to the square of the distance from which it is viewed.

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....

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

A device similar to distributed feedback lasers in construction and operation, but in which the period grating that produces feedback is removed from the gain region to simplify fabrication. The...

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...

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.

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 transparent crystalline substance that is anisotropic relative to the velocity of light.

A laser that sends data from the source to the distribution node.

In a dual-ring local area network, a node that is connected both to the primary, active ring and also to a secondary ring that provides redundancy in case of cable or system failure.

An optical system having two sets of components separated by an air space, while successive lenses in each set are cemented together.

An instrument that uses a photoelectric system to determine the size and volume of dust particles in a given unit of air.

A microscope that has been modified to permit the quantitative analysis of dust samples.

In atmospheric optics, the almost total blocking of light transmission in the atmosphere due to the scattering and absorption of the light by dust particles.

A type of mosaic detector array that combines features of scanning and staring sensors by using a small rapid scanning motion (see saccadic motion) over a few pixels at a time.

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...

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 lightproof box used for storing photosensitive materials.

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

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

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

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 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.

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