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Photonics Dictionary: G

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GOSIP
government open systems interconnection profile
GPC
graphics performance characterization
GPIB
general-purpose interface bus
GPON
Gigabit passive optical network
GPS
global positioning system
graded index
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...
graded reflectivity mirror
A mirror whose percent reflectance varies as a function of position on the mirror surface.
gradient
In image processing and machine vision, the rate of change of pixel intensity.
gradient edge enhancement
Edge enhancement with a directional characteristic.
gradient vector
In an image, the orientation and magnitude of the rate of change in intensity at any point.
gradient-index profile
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...
graduated refractive index -> graded index
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...
grain boundary
In a multicrystalline material, the meeting point between crystallites.
grain isolating diaphragm
In a microscope, the diaphragm located between the Bertrand lens and the eyepiece, which is closed during conoscopic viewing to restrict the interference figures to that of a crystal lying on the...
gram negative
Gram-negative bacteria are a group of bacteria that possess a cell envelope composed of a thin layer of peptidoglycan surrounded by an outer membrane. This outer membrane contains lipopolysaccharides...
gram positive
Gram-positive bacteria are a group of bacteria that have a thick cell wall composed primarily of a substance called peptidoglycan. This thick peptidoglycan layer retains a stain called crystal violet...
gram
Unit of mass in the SI system.
graphecon
An electron tube having two electron guns, one on each side of the storage medium, to encode the information onto the medium, and to read and simultaneously erase the electrostatic encoding.
graphene
Graphene is a two-dimensional allotrope of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice pattern. It is the basic building block of other carbon-based materials...
graser
An acronym of gamma ray amplification by stimulated emission of radiation. It is a gamma ray laser that operates between energy levels established by metastable isomeric transitions in the nucleus.
graser
gamma ray amplification by stimulated emission of radiation
Grashof number
Formula used in convection study to express the ratio of buoyant force to viscous force.
graticule
The British term for reticle.
grating
A framework or latticework having an even arrangement of rods, or any other long narrow objects with interstices between them, used to disperse light or other radiation by interference between wave...
grating beamsplitter
A grating beamsplitter is an optical device that utilizes the principles of diffraction to split a beam of light into multiple beams, often redirecting them at specific angles. It is based on the...
grating monochromator
An optical instrument used to isolate a narrow bandwidth of optical radiation using a diffraction grating as the dispersive element. See also monochromator.
grating prism
A specific, right-angle prism having a transmission grating replicated on its hypotenuse face and used in applications requiring a system that can produce in-line viewing for one wavelength.
grating spectrograph -> spectrograph
An optical instrument for forming the spectrum of a light source and recording it on a film. The dispersing medium may be a prism or a diffraction grating. A concave grating requires no other means...
grating spectrometer
A spectrometer that uses a grating to diffract light into specific wavelengths.
grating spectroscope
A spectroscope having a diffraction grating for the resolution of light of various wavelengths.
grating substrate
The substrate upon which a diffraction grating will be ruled. It must be dimensionally stable, and the surface must be polished to an accurate flat or spherical form as required by the grating. The...
gravimeter
An instrument capable of precise measurements of the Earth's gravity. This permits the detection of small changes in local height that indicate changes in the Earth's crust and subsurface density.
gravitational imaging
A process used to detect minute gravitational fields and to display images from objects by means of radiated gravitational imagery.
gravitational lens
The effect of a powerful gravitational field on light traveling through the field. This effect is detectable in astronomical observations when light from a distant source passes a massive object...
gravitational waves
Postulated by Einstein in his theory of relativity. They are waves traveling at the speed of light and exerting force on matter in their path. They are produced by changes in the distribution of...
gray body
A temperature radiator whose spectral emissivity at all wavelengths is in constant ratio (less than unity) to that of a complete radiator at the same temperature.
gray filter -> neutral density filter
A light filter that equally decreases the intensity of all wavelengths of light without altering the relative spectral distribution of the energy.
gray levels
In image processing, machine vision and television, discrete brightness values quantized for a group of pixels. They can range from white, through various shades of gray, to black.
gray scale
In image processing, the range of available gray levels. In an 8-bit system, the gray scale contains values from 0 to 255.
gray scales
Transparencies that represent progressive steps in the amount of transmitted radiation for administering predetermined amounts of radiation to a radiation-sensitive substance. The steps are...
gray
1. A measure of absorbed dose, equal to the energy imparted by ionizing radiation to a mass of matter corresponding to 1 J per kilogram. 2. A term used to denote an incompletely polished surface that...
gray-scale image
An image consisting of an array of pixels that can have more than two values (black and white). Typically, up to 16 levels are possible per pixel.
gray-scale modification
Image enhancement operations that involve altering gray-scale values. For instance, brightness sliding involves adding or subtracting an identical brightness value to or from each pixel in an image;...
grazing emergence
A condition in which an emergent ray is perpendicular to the normal of the emergent surface of a medium.
grazing incidence
Light striking a surface at an angle almost perpendicular to the normal.
green block
A porous ceramic substance that is ground to a given optical form and on which a polished plate of glass is sagged by heat application. It is capable of transmitting in a partial vacuum. The glass...
green disc
Familiar term for CD/I disc. The CD/I standard also is known as the green standard.
Greenough microscope
A form of a stereoscopic microscope having paired objectives, prisms and eyepieces, and invented by H. Greenough.
Gregorian telescope
A telescope with an ellipsoidal secondary concave mirror that reflects rays from a parabolic primary mirror through an opening in the center of the primary, where the image is viewed with an eyepiece.
grenz rays
The soft x-rays used in the industrial radiography of materials having too small a range of densities to produce an image with normal x-rays.

Photonics DictionaryG

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