Photonics Dictionary: A

The process by which a substance, usually a solid, attracts and retains on its surface the molecules of another substance.

A chemical placed in a solution that will indicate when an excess of a substance or ion has been reached by coloring the precipitate after the chemical itself has been totally adsorbed.

A television format with enhanced vertical resolution (400 lines as compared with the standard 330) that, unlike high-definition television, can operate on existing bandwidths and with existing...

Advanced driver assistance systems (ADAS) refers to a set of safety features and technologies designed to assist drivers in the driving process and enhance overall vehicle safety. These systems use...

An accelerator at the Argonne National Laboratory, providing powerful x-ray beams for materials research applications.

A glow discharge lamp consisting of a cold cathode and a mixture of inert gases. The intensity of illumination varies with the applied signal voltage. This lamp was commonly used as a source of...

Film designed especially for the needs and conditions encountered in aerial photography. It is produced in a variety of widths, lengths and emulsions.

An optical illusion in which distant objects are lighter in tone and less distinct in outline than those closer to the observer because of the atmospheric diffusion of light.

The application of aerial photographs as a means of measurement in map making and surveying.

The use of optical or electronic recording systems to extract information from the terrain, while aloft, for reconnaissance applications.

The creation of a planned sequence of data input that is obtained while airborne for use in aerial photogrammetry and other types of map making and surveying. The data can be photographic, electronic...

The creation of topographical maps and charts from a stereographic record produced through the overlapping of consecutive aerial photographs by more than 50 percent.

In aerial photography, the geometric method of indicating the three-dimensional location of ground points from a pair of aerial photographs.

Transformation of an image, such as a change in position or scale, that does not alter the linearity of the original image.

A visible laser beam generated coaxially with an infrared or other invisible laser beam to aid in its positioning.

A support device in which a column or chamber of air permits the free travel of a mobile part. In optical mounting and positioning equipment, air bearings are of two types, linear or rotary,...

A quantitative measure of the amount of radiation given off by an instrument, expressed in roentgens per unit of free air.

A category of systems designed to communicate a photo taken from the air (e.g., aircraft, balloon, satellite) to a ground station. It can be done by direct television transmission of the photo, or by...

Diffuse light emitted by the atmosphere due to the excitation of particles of atmospheric gas. These excited particles release light that is visible from Earth as a faint luminescence in the night...

The equation devised by Sir G.B. Airy for the analysis of light diffraction near a caustic surface: (d2f/dz2) - zf = 0 where z represents the independent variable, and f is the value of the function.

The central peak (including everything interior to the first zero or dark ring) of the focal diffraction pattern of a uniformly irradiated, aberration-free circular optical element or system.

The ratio of radiant energy reflected from a rough surface to that incident on it. Usually, the radiant energy is total solar energy; thus, it is not a spectral quantity.

An alexandrite laser is a solid-state laser that utilizes a synthetic crystal made from the rare earth element alexandrite (BeAl2O4:Cr3+). This crystal is capable of emitting laser light in the...

An old name for the rotating arm moving about an axis of rotation over a divided circle used to measure angles. Now the term refers to a small stadia telescope mounted over a ruler for use in...

A laser, usually employing helium-neon or other gases as the active medium, used for alignment in industrial applications.

A photocell having an alloy junction formed by combining an indium disc with a thin wafer of N-type germanium.

A 2-million W, 2.7-µm-wavelength hydrogen-fluoride laser used as a directed energy weapon.

In computer graphics, a character generator that produces alphabetical and numerical characters with some punctuation and symbols.

A type of telescope mount that permits direct azimuth and elevation adjustments.

A cathode-ray tube having a screen that is coated on the back with a thin film of aluminum, which serves to intensify the propagation of light.

The process of applying a film of aluminum to a surface, usually by evaporation in a vacuum.

Light present in the environment around a detecting or interpreting device, especially a machine vision system, and generated from outside sources. Such light must be treated as noise by the vision...

The underexposed collodion that is present on a glass negative as a positive when backed with material.

Also known as roof prism. A type of prism designed by G.B. Amici. It consists of a roof edge produced upon the long reflecting face of a right-angle prism. Used as an erecting system in elbow and...

Broadband radiation emitted by a laser that does not transmit through the optical element. It can be removed by filtering.

A hologram in which diffraction is produced by the silver image, resulting in a dimmer image than in a phase hologram, where diffraction takes place at the gelatin relief image left once the silver...

In digital data transmission, the representation of a bit by change in amplitude of the outgoing signal. Amplitude shift keying (ASK) is less sensitive than phase-shift keying, but can tolerate...