Photonics Dictionary

A photocathode that receives radiation from one side and emits a photoelectric current from the opposite side.

A type of compensator for use with a microscope and consisting of a quarter-wave plate in a fixed position and a rotatable analyzer.

A polarizing beamsplitting prism similar in design to the Rochon prism. However, the Senarmont transmits the extraordinary ray without deviation and deviates the ordinary ray due to the orientation...

In a radiation detector, the ratio of the output to the input signal.

The optical energy transfer between ions of differing atoms.

An instrument for determining the sensitivity of a photographic film to light. The film is given either a stepped exposure or a continuously varied exposure; after processing, the density is measured...

Primarily the measurement of photographic sensitivity of certain materials such as photographic film. It refers to the measurement of the response of photographic materials, after exposure, to forms...

1. A generic term for detector. 2. A complete optical/mechanical/electronic system that contains some form of radiation detector.

An avalanche photodiode in which the light-absorbing area is a low-bandgap material and the PN junction is placed in an area of high-bandgap material, reducing dark current and increasing gain.

Three filters used in making a color print of a color negative, red, green and blue-violet, respectively. Each filter transmits about one-third of the visible spectrum onto the print.

A type of motion-picture camera in which single frames are photographed either automatically at a predetermined rate (as slow as one frame per minute or hour), or whenever the operator presses a key....

With respect to television, the transmission of the signals that originate from variously colored parts of an image in a particular sequential order.

Raster scanning process like that of television: each line is scanned successively.

A mode of data transmission whereby each bit is generated in sequence on a single carrier.

A variation of tomography, which is a means of visualizing any one of a large set of parallel planes in the patient. A series of x-ray pictures taken from different angles results in developed...

A device used in measuring attenuation in optical fiber. The loss caused by the bends in a short reference length of fiber approximates that of a much longer fiber under test.

A closed-loop system that is constantly adjusted in response to input signals generated within the system.

A type of motor that acts as the control element in a servomechanism. It is powered by an amplifier circuit and drives the load with linear or rotary motion.

A handheld navigational instrument used to measure the elevation angle of celestial bodies such as the sun. An image of the sun is viewed through a small telescope via two plane mirrors so that any...

The Shack-Hartmann wavefront sensor is an optical device used for measuring the wavefront aberrations of an optical system. It is widely used in adaptive optics systems to correct distortions and...

1. The sorting of lenses by their color. 2. In an optical system, an irradiance or brightness gradient in the image that is not present at the object.

A type of color-generating cathode-ray tube that uses a shadow mask, a thin perforated electrode, located close to the display screen. Each hole in the mask coincides with a triad of three phosphor...

A method of demonstration or examination using a point source illumination without the use of any projection lens between the object and its shadow, the shadow being cast on a distant screen.

A term used to denote a concave surface having too long a radius of curvature. That is, its negative power is too small or low.

A term used to describe a convex surface having too short a radius of curvature. To correct this condition, material is cut from the outer portion of the polishing tool.

The distance between the base and the vertex before the edging of a prism.

A function of the intensity distribution in an image aberrated by a quadratic curvature wavefront distortion.

Image distortion that occurs when the axes of the original image are not perpendicular in the resulting image, making the resulting image appear slanted. Shear can be caused by movement of the...

An interferometer in which interference is produced between wavefronts that are sheared in the sample object by a small lateral distance.

A three-dimensional grating designed with thin metal sheets to remain opaque to all but one specific and predetermined wave.

A sheet of plastic material containing microscopic crystals of herapathite or some other similar substance that transmits light polarized in one direction, but absorbs light polarized in a...