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8,236 terms
Photonics Dictionary
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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.
GRIN lens
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...
grinding
The process in the manufacture of an optical system that gives it the required geometric shape.
grinding and polishing machinery
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...
grinding tool
A tool of cast iron or another suitable medium used with a slurry of silicon carbide, aluminum oxide or emery for grinding optical surfaces.
GRINSCH
graded-index separate confinement heterostructure
Grittington test
A method of determining the abrasion resistance of very hard materials by passing a weighted wiper blade across them in a sand-water slurry for a specified number of times.
ground glass
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...
ground state
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...
ground truth
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...
group index
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...
group velocity
For a particular mode, the reciprocal of the rate of change of the phase constant with respect to angular frequency.
grown-junction photocell
A photodiode that has been designed so that the bar of semiconductor material has a PN junction perpendicular to its length and an ohmic contact at each of its ends.
GSGG
gadolinium scandium gallium garnet
GSP
graphics system processors
GTC
gain time constant; gain time control
GTI
Gires-Tournois interferometer
GTL
gas transport laser
Gudden-Pohl effect
The light flash that occurs when an electrical field is applied to a phosphor already excited by ultraviolet radiation.
guide factor
A factor derived by equating the incident light on the subject to the required incident light for suitable photography. The lamp-subject-distance then is multiplied by the aperture and solved in...
guided mode
In an optical waveguide, a mode whose field decays monotonically in the transverse direction everywhere external to the core and which does not lose power to radiation. Also called bound mode.
guided ray
In an optical waveguide, a ray that is completely confined to the core.
guided wave
A wave in which energy is focused near a boundary separating materials having different properties. Propagation of the wave is in a direction parallel to the boundary.
gun camera
A camera accurately aligned to a weapons system to provide a photographic record of system performance.
gunsight
An optical device that permits the alignment of a gun, cannon or rocket launcher system with its target.
GVD
group velocity dispersion
gyroscope
A gyroscope is a mechanical device consisting of a spinning disk or wheel mounted on a spinning axis in such a way that its orientation remains fixed regardless of any movement of its mounting...
gyroscopic camera mount
A mount that uses a floating suspension and a motor-driven gyroscope to keep a motion picture or still camera at a set angle even though the camera is mounted in a place that subjects it to heavy...
gyroscopy
Gyroscopy refers to the principles and applications of gyroscopes, devices that measure or maintain orientation based on the principles of angular momentum. Gyroscopes are essential in various...
h
henry; hecto-; hour; Planck constant
H-plane bend
With respect to waveguides, the continuous change in the direction of the axis of the wavelength, during which the axis is perpendicular to the direction of polarization.
hackle
A defect in the cleaved end face of an optical fiber, defined as multiple surface irregularities across the fiber surface. A less serious imperfection of the same nature is known as mist.
HADAR
heat-assisted detection and ranging
Haidinger fringes
Also known as constant angle or constant deviation fringes. The interference fringes observed with dense flat plates near normal incidence. The fringes of the Fabry-Perot interferometer are Haidinger...
hair-trigger operation
Triggering a laser at a predetermined time by pumping it to a level just below its threshold and then using an auxiliary source that quickly pumps it above threshold. Means of achieving it in laser...
halation
1. In a cathode-ray tube, the glow surrounding a bright spot that appears on the fluorescent screen as the result of the screen's light being reflected by the front and rear surfaces of the tube's...
half bandwidth
The term half bandwidth (HBW) generally refers to the width of a spectral band or frequency range at half of its maximum amplitude. It is commonly used in the context of signal processing, optics,...
half duplex
A communications system that can transmit in only a single direction at a time. See duplex.
half silvered
Describing a surface that is coated with a film of metal of such thickness that it transmits about one-half of the incident light and reflects about one-half.
half wave
Refers to half a wave cycle.
half-power point
1. The value on either the leading or the trailing edge of a laser pulse at which the power is one-half of its maximum value. 2. The wavelength at which a filter is transmitting one-half of its peak...
half-shade device
A device for forming at least two adjacent areas of polarized light. The angle between the directions of vibration of the light waves in the two areas is generally small.
half-shade plate
A semicircular, half-wave quartz plate between the polarizer and analyzer. It often is used in forming precision settings with a polariscope.
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Photonics Dictionary
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