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364 terms

Photonics Dictionary: P

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positron -> electron

A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is...

panoramic telescope

A telescope so manufactured that the image remains erect and the position of the eyepiece is unchanged as the line of sight is pointed in any horizontal direction.

parallel beam -> collimated radiation

Radiation in which every ray from any given object point can be considered to be parallel to every other. This is never completely the case: The light from a star is really diverging, and all...

parallel processing

In imaging, the processing of pixel data in such a way that a group of pixels is analyzed at one time rather than one pixel at a time.

parallel scanning

Parallel scanning refers to a method of acquiring data or images simultaneously from multiple sources or in parallel, rather than sequentially scanning each source one after another. This approach is...

parallel transmission

A mode of data transmission whereby bits of information are carried simultaneously at different frequencies over a single channel.

parallel-plate waveguide

A pair of waveguides with axes normal to the plane and that guide uniform cylindrical waves.

parallel/serial converter

A device that converts data transmitted in the parallel mode to a sequence of bits at a single frequency for output in the serial mode.

parallelogram distortion

In a camera or cathode-ray tube, distortion that is designated by a lateral skewing of the reproduced image.

particle acceleration

Particle acceleration refers to the process by which charged particles, such as electrons or protons, gain kinetic energy and increase their velocity. This acceleration can occur in various natural...

particle image velocimetry

A whole-flow-field technique providing instantaneous velocity vector measurements in a cross-section of a flow that is seeded with micron-sized particles. CCD or CMOS cameras and laser light sheets...

peak wavelength

The wavelength at which the radiant intensity of a source is maximum.

peel point

In a fiber optic guided missile, the point at which the optical fiber pays out from the bobbin on which it is wound.

pel

Contraction of "picture element." See pixel.

pellicle mirror

A thin, stretched plastic membrane cemented to a rigid supporting ring. It may be coated to act as a beamsplitter, for example, in a color camera; it is so thin that no perceptible image doubling...

Pellin-Broca prism

A form of dispersing prism, often used in monochromators, that consists of a common right-angle prism with a 30° dispersing prism attached to each of its square faces. The spectrum formed by the...

Peltier cooler

A Peltier cooler, also known as a thermoelectric cooler (TEC) or thermoelectric module, is a solid-state device that uses the Peltier effect to transfer heat between two electrical junctions. It can...

Peltier effect

See thermoelectric cooling.

phase velocity

For a particular mode in a waveguide, the ratio of the angular frequency to constant phase.

photoacoustic gas cell

A device for measuring absorption coefficients in which a confined, nonabsorbing gas fills the space inside the cell between the two windows, which are made from a weakly absorbing medium.

photocell -> detector

1. A device designed to convert the energy of incident radiation into another form for the determination of the presence of the radiation. The device may function by electrical, photographic or...

photoconductive cell -> photoconductive detector

A device for detecting visual and infrared radiation using a photoconductor as the principle sensing element.

photodielectric effect

The effect, present in particular phosphors, that is defined as a transformation in the dielectric constant of a material when illuminated.

photoelastic constant

A formulaic description of the linear change of the reciprocal optical dielectric tensor with either stress or strain.

Photoelastic equipment and supplies

Photoelastic equipment and supplies refer to instruments and materials used in photoelasticity, a technique used to analyze stress distribution and behavior in materials. photoelastic equipment...

photoelastic

In optics, the double refraction that is produced when stress is applied to a transparent material. Plastics, which are especially photoelastic, can be formed into models of structures that are...

photoelasticity

The process of determining, with the aid of plane-polarized light, the stress distribution in materials under complex systems of loading.

photoelectric absorption

The transformation of incident radiant energy into a photoelectric emission current.

photoelectric cathode

A cathode principally designed to emit a photoelectric current.

photoelectric colorimeter

A system having a photoelectric detector for the measurement of three quantities related by linear combination to tristimulus values of a sample.

photoelectric colorimetry

The measurement and analysis of color using a photoelectric instrument having three filters with broad spectrum bands.

photoelectric constant

The constant that, multiplied by the frequency of the radiation-producing emission of photoelectrons, determines the amount of voltage each photoelectron absorbs.

photoelectric control

The control of an instrument or electrical circuit by the current produced by varying radiation incident to a photoelectric cell.

photoelectric counter

A device used to count objects that pass a given point by allowing each object to obstruct a beam of light falling on a photocell. Slow counting rates can be recorded by a mechanical counter, but...

photoelectric current

The electron stream emitted by a phototube when the cathode is exposed to light.

photoelectric densitometer -> densitometer

1. An instrument used to measure the opacity or density of dyes, pigments or dispersed particles that form an image in or on a medium, such as a photographic film. 2. A device used to measure the...

photoelectric effect

The emission of an electron from a surface that occurs when a photon impinges upon the surface and is absorbed. This effect is the means by which photons may be detected.

photoelectric emission

The electron emission from a substance or instrument whose surface has been bombarded by a suitable amount of radiation.

photoelectric exposure meter

A device consisting of a microammeter, a photovoltaic cell and a battery. It is used for the measurement of scene brightness and the determination of correct exposure for photographic processes.

photoelectric fluorometer

A filter fluorometer that uses a photomultiplier tube to detect the fluorescence of a sample.

photoelectric mixing

Also known as light beating. The mixing of two narrowband optical components to produce an AC component in the photocurrent at the optical difference frequency.

photoelectric multiplier

A phototube in which the primary photoemission current, before being extracted at the anode, is multiplied many times.

photoelectric photometer

Also known as electronic photometer. A photometer with a photocell, phototransistor or phototube for measuring the intensity of light.

photoelectric photometry

The use of photoelectric sensors to detect and measure the intensity of a light source. This application, as compared to human observation, results in higher speeds of operation, a greater...

photoelectric pyrometer

An instrument used to measure the temperature of a source through the use of photoelectric cells to detect and measure the intensity of the light emitted by the source.

photoelectric reader

An input device for a computer that detects and reads the data, in the form of punched holes in cards, by light that is transmitted through the holes.

photoelectric receiver

An instrument that uses a photocell to detect and measure the intensity of incident light.

photoelectric reflectometer

A photoelectric photometer used to measure the reflectance of a surface.

photoelectric relay

A relay that opens or closes an electrical circuit depending on the intensity of the light incident to a photoelectric device contained in the relay.

photoelectric scanner

A system mounted a few inches above a moving plane that consists of a light source, lenses and one or more phototubes. In this position, the scanner actuates the control equipment when the quantity...

Photonics DictionaryP