Photonics Dictionary: G

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

Descriptive of an optical fiber having a core refractive index that decreases almost parabolically and radially outward toward the cladding. This type of fiber combines high bandwidth with moderately...

The term gradient-index profile refers to a specific type of refractive index distribution within an optical material. In optics, the refractive index of a material describes how much the speed of...

In a multicrystalline material, the meeting point between crystallites.

The process in the manufacture of an optical system that gives it the required geometric shape.

Machinery used to grind and finish a component, such as a lens or prism, to a desired precision. Usually such machines carry a cup-shaped or flat tool (lap) into close contact with the part. An...

A tool of cast iron or another suitable medium used with a slurry of silicon carbide, aluminum oxide or emery for grinding optical surfaces.

A plate of glass in which a face has been frosted by grinding or etching. It diffuses light by scattering in directions close to the incoming beam, but the light falls off rapidly at larger angles...

Also known as ground level. The lowest energy level of an atom or atomic system. A material in the ground state is not capable of emitting optical radiation. All other states are called excited...

A term variously applied to remote sensing techniques that essentially refers to all parametric conditions that influence the sensor system; includes the quantitative reality that the sensor sees and...

For a given mode propagating in a medium of refractive index n, the velocity of light in vacuum c, divided by the group velocity of the mode. For a plane wave of wavelength l, it is related to the...

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...

An optically pumped solid-state laser in which the active medium is a neodymium ion in a glass rod host. Abbreviated Nd:glass.

A GRIN (gradient index) lens is a type of optical lens that utilizes a gradient in refractive index across its volume rather than having a uniform refractive index like conventional lenses. This...

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...

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 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...

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.

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

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

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 (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 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...

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....

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.

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...

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.

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...

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) 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...

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...

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

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

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...

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...

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...

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

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...

A telescope objective with excellent spherochromatic correction, consisting of a meniscus crown and a meniscus flint, both convex to the long conjugate.

A beam of light whose electrical field amplitude distribution is Gaussian. When such a beam is circular in cross section, the amplitude is E(r) = E(0) exp [-(r/w)2], where r is the distance from beam...