Photonics Dictionary

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

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

The area of optics that deals with the propagation of Gaussian laser beams in free space, or any general medium - i.e. lenses- under the paraxial (small divergence angle) approximations. Gaussian...

An intensity distribution (intensity as a function of radial distance from the beam center) which is given by the Gaussian function: where: I0 is the intensity at the beam center r is the radial...

Also called Geiger-Müller counter. An instrument designed to detect and measure radioactivity through the use of a gas-filled metallic tube containing a needle electrode. Radiation traveling...

A device used to lock the internal synchronization generator of a television camera to an external source.

The physical center of the lens; it is on the axis of the lens, halfway between the front and rear vertex. It is sometimes referred to as the mechanical center of the lens.

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 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...

A man-made satellite that orbits 35,680 km from the Earth at a rate of one orbit per 24-hour period, thereby retaining its initial relative alignment with the Earth.

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

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...

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...

A device similar to the ordinary spectrophotometer but containing particular modifications to provide for the comparison of two sources.

A prism resembling a Nicol prism but having faces normal to the axis and the two parts divided by a glycerine film. Also known as Glan prism.

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...

A type of glass containing barium oxide, which is added to increase the refractive index while maintaining a relatively low dispersion.

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.

The total radiation, both solar and diffuse sky, that is incident to a unit's horizontal surface.

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.

An electric discharge in a low-pressure gas having a low-current density and a space potential near the cathode that is much higher than the ionization potential of the gas but less than its sparking...

A lamp in which the ionization of the inert gas contained in it produces a glow in the space close to the negative electrode.

In an image, the orientation and magnitude of the rate of change in intensity at any point.

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.

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...

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...

An optical instrument used to isolate a narrow bandwidth of optical radiation using a diffraction grating as the dispersive element. See also monochromator.

A spectroscope having a diffraction grating for the resolution of light of various wavelengths.

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.

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...

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...

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;...

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.

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...

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 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.

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...

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.