Photonics Dictionary: G

Trade name referring to an instrument that determines surface distances by measuring the length of time it takes for a modulated lightwave to reach a mirror and be reflected to its point of origin.

The position and shape of the image of a point source, as predicted by geometric optics alone. The geometric image is to be differentiated from the diffraction image, which is determined from...

In image processing, mathematical operations that change spatial geometry, as for instance scaling, translating, rotating or otherwise manipulating the perspective. Also called geometric manipulation.

A field of physics that deals with light as if it truly were composed of rays diverging in various directions from the source and abruptly bent by refraction or turned by reflection into paths...

A technique used to create an achromatic phase shift based on the principle of geometric phase. The phase shift is experienced by a light beam as a result of a cyclic change in its state of...

The area of optics in which the propagation of light is described by geometrical lines (or rays) governed by Fermat's Principle. Geometrical optics is useful as long as the objects in which the light...

The superposition of satellite or aerial images with a map in order to process and remove distortion. Uses reference points from map to align and apply information.

A type of glass used in near-infrared optical components, in which germanium is used as a cation instead of silicon.

A crystalline semiconductor material that transmits in the infrared.

Germicidal ultraviolet (GUV) refers to a specific range of UV radiation that has disinfectant properties capable of killing or inactivating microorganisms, including bacteria, viruses, and fungi. The...

A prefix that is used to represent 109 or 1,000,000,000 in the SI system.

GigE, short for gigabit Ethernet, refers to a standard for high-speed Ethernet communication, capable of transmitting data at rates of up to 1 gigabit per second (Gbps), or 1000 megabits per second...

An optical mounting device that permits adjustment around two perpendicular and intersecting axes of rotation.

An interferometer similar in construction to a Fabry-Perot interferometer but having a rear mirror with high reflectivity, allowing light to escape only at the partially reflective front mirror.

A type of birefringent polarizing prism that transmits the extraordinary ray and removes the ordinary ray through total internal reflection. It consists of two calcite prisms with an air gap...

A noncrystalline, inorganic mixture of various metallic oxides fused by heating with glassifiers such as silica, or boric or phosphoric oxides. Common window or bottle glass is a mixture of soda,...

A furnace, generally electrically heated, with a control system capable of following a cam by which the temperature can be made to go through a definite cycle over a period of days, or even weeks, if...

An early form of photographic media consisting of glass plates coated with an emulsion.

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

Ink used for writing on glass, and also for blackening the edges of lenses to prevent reflection. In the latter case, the refractive index of the ink must closely match that of the glass.

A type of glass used in telescope mirrors, formed by adding a nucleating agent to standard glass and then heating it until it crystallizes.

The plane shared by the pair of axes in a twin crystal.

A controlled random search process, such as generalized simulated annealing, that has been incorporated into many optical design programs as a way of helping designers find the most suitable lens...

A light source made up of silicon carbide or carborundum. It is resistant to the negative temperature coefficient and mechanical distortion.

A crystal of microscopic size having no definite plane faces and having a globular shape. At the time the crystal is formed, the strong surface tension influences the formation of the plane faces.

A thermal radiation detector consisting of a small cell with a blackened plastic front face that bulges slightly when heat is received by it. The bulging tilts a small mirror, which, in turn, varies...

A neutral-colored gelatin wedge, cast between glass plates, that is used as an intensity scale in certain types of sensitometers; the greater the thickness of the wedge through which light emitted by...

A device used to measure directional reflectance, with light collection restricted to a narrow range of angles of which the central angle varies.

The graphed curve illustrating the directional reflectance of a sample for different angles of collection.

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...

Edge enhancement with a directional characteristic.

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.

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 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 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...

Unit of mass in the SI system.

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 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...

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.

Formula used in convection study to express the ratio of buoyant force to viscous force.

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...

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...