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Photonics Dictionary: G

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G

giga-; gauss

gram; groove

acceleration of gravity

GaAlAs laser

A GaAlAs laser is a type of semiconductor laser diode that emits light in the near-infrared region of the electromagnetic spectrum. It is composed of layers of gallium, aluminum, and arsenic, hence...

GADS-CAG

gadolinium scandium aluminum garnet

gain coefficient -> absorption coefficient, absorption cross section

The transition cross section constant coefficient which defines the transition probability of absorption from ground to a higher level within a given atomic or molecular species. The transition...

gain

Also known as amplification. 1. The increase in a signal that is transmitted from one point to another through an amplifier. A material that exhibits gain rather than absorption, at certain...

gain-bandwidth product

In an avalanche photodiode, the gain multiplied by the signal frequency in MHz.

gain-guided laser

A laser diode in which the beam is confined to the region of the active layer with gain high enough to accomplish such confinement without a built-in refractive index profile. That region generally...

gain-switching

Gain-switching is a technique used in lasers to generate short pulses of light by modulating the gain of the laser medium. This method is distinct from Q-switching and mode-locking, two other common...

Galilean telescope

A refracting telescope that yields an erect image by the use of a positive lens for its objective and a negative lens for its eyepiece.

gallium aluminum arsenide

A crystalline semiconductor alloy used as the light confinement layer in both single- and double-heterostructure diode lasers.

gallium antimonide

A binary semiconductor compound used as a substrate or active layer for diode lasers.

gallium arsenide injection laser

A laser system consisting of a planar PN junction within a single crystal of gallium arsenide. The pair of parallel, semireflective end faces produces a Fabry-Perot resonant cavity, whereas the other...

gallium arsenide phosphide

Gallium arsenide phosphide (GaAsP) is a semiconductor alloy composed of gallium (Ga), arsenic (As), and phosphorus (P). It is commonly used in the fabrication of optoelectronic devices, particularly...

gallium arsenide

Gallium arsenide (GaAs) is a compound semiconductor material composed of gallium (Ga) and arsenic (As). It belongs to the III-V group of semiconductors and has a zincblende crystal structure. GaAs is...

gallium nitride

Gallium nitride (GaN) is a compound made up of gallium (Ga) and nitrogen (N). It is a wide-bandgap semiconductor material that exhibits unique electrical and optical properties. Gallium nitride is...

galvanoluminescence

The emission of radiant energy produced by the passage of an electrical current through an appropriate electrolyte in which an electrode, made of certain metals such as aluminum or tantalum, has been...

galvanometer mirror

A small mirror, sometimes plane and sometimes concave, attached to the rotating coil of a galvanometer to cause a spot of light to move along a scale.

galvanometer

A galvanometer is an instrument used for detecting and measuring small electric currents. It typically consists of a coil of wire suspended in a magnetic field, with a pointer attached to the coil....

galvanometric scanner

A galvanometric scanner, also known as a galvanometer scanner or galvo scanner, is a type of optical scanning device used to rapidly and precisely direct a laser beam or other light source to...

galvo-directing mirrors

A system of mirrors that can be used to direct light from a single laser source into any one of a number of separate optical fibers.

gamma

A numerical value representing the degree of contrast in a television picture: the exponent of the power law used to approximate the curve of output magnitude vs. input magnitude over the region of...

gamma camera

A camera used in scintillation recording to make a visible record of the distribution and relative concentration of radioactive tracer elements in a sample that is undergoing scanning.

gamma correction

Modification of a system to provide for a linear transfer characteristic from an input to an output device. A circuit for this purpose is built into a television camera to compensate for display tube...

gamma radiography

Radiography using the emission of gamma rays to form an image of the structure penetrated by the radiation.

gamma ray

The spontaneous emittance of electromagnetic radiation by the nucleus of certain radioactive elements during their quantum transition between two energy levels. The radiation emitted has a wavelength...

gamma-ray spectrometer

An instrument used to detect and measure the energy distribution of gamma rays. It has been used to chart the radioactivity at the lunar surface.

GaN

gallium nitride

GaN distributed feedback lasers

GaN (gallium nitride) distributed feedback (DFB) lasers refer to a specific type of semiconductor laser based on Gallium Nitride materials and designed with a distributed feedback structure. These...

GaN-based LEDs

Gallium nitride-based light-emitting diodes (GaN-based LEDs) are semiconductor devices that emit light when an electric current passes through them. These LEDs are constructed using gallium nitride...

gap loss

The optical power loss caused by a space between axially aligned fibers.

gas current

The positive ion current created in an electron tube as a result of the collisions between electrons and residual gas molecules.

gas discharge

The conduction of electricity in a gas as a result of the ions generated by collisions between electrons and gas molecules.

gas discharge display

A display device that contains an inert gas that gives off orange light when a high voltage is applied to ionize the gas.

gas discharge laser -> gas laser

One of the first lasers to find practical application. Generally, the pumping mechanism is an electric discharge, although some high-power forms employ chemical reaction or gas compression and...

gas filter correlation

A technique for measuring the concentration of any gases. Identical infrared beams are alternately chopped, one passing through a reference cell and the other passing through a cell with the gas...

gas focusing -> ionic focusing

Also known as gas focusing. The introduction of an inert gas into a cathode-ray tube for the concentration of the electron beam. The gas molecules are ionized by the electrons, producing a core of...

gas laser

One of the first lasers to find practical application. Generally, the pumping mechanism is an electric discharge, although some high-power forms employ chemical reaction or gas compression and...

gas magnification

The increase in current of a phototube as a result of the gas in the tube becoming ionized.

gas photocell

A photoemissive cell having an inert gas added to its envelope. Subsequent ionization of the gas increases the responsivity of the photocell.

gas phototube

A phototube having increased response due to the addition of a quantity of gas.

gas tube

An electron tube whose current flow is affected by the pressure on the gas or vapor contained in the tube.

gas-transport laser

A gas laser wherein the gas mixture is not exhausted into the atmosphere but is continually recycled. It is excited in the active region, cooled and re-excited. The GTL requires no constant gas...

GASP

graphic applications subroutine package

gastroscope

An optical instrument designed for the visual examination of the inside of the stomach.

gateable

In detectors, the ability to switch on and off electronically, thus producing the effect of a mechanical shutter.

gated image tube

An intensified charge-coupled device that uses a large negative charge at the grid to switch off the flow of electrons at periodic intervals in order to provide a clearer output image when adverse...

gated integrator -> boxcar averager

An instrument for detecting and analyzing repetitive signals. Using a fixed time delay or "gate," the input signal is sampled numerous times and averaged to increase the ratio of the...

gated pulse

A discontinuous burst of laser light generated by timing or "gating'' a continuous-wave laser.

Photonics DictionaryG

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