Photonics Dictionary

The emission and/or propagation of energy through space or through a medium in the form of either waves or corpuscular emission.

Half the vertex angle of the cone of light emitted by a fiber.

An instrument used to recognize and identify incident radiation by the ionizing or stimulating properties of the radiation.

Any of the many devices used to detect the presence of radiation from a specific region of the electromagnetic spectrum.

The detection and measurement of nuclear and x-ray radiation.

The average length in a specific material in which a relativistic charged particle will lose 67 percent of its energy by bremsstrahlung.

A mode in an optical waveguide whose fields are transversely oscillatory everywhere external to the waveguide. It exists even in the limit of zero wavelength.

Relative power distribution as a function of position or angle.

The force exerted on a surface by radiation.

Also known as radiation thermometer. A pyrometer in which the radiant intensity from the source to be measured is used to calculate its temperature. The usual detector is a thermocouple, thermopile...

The temperature of a complete radiator that has a total radiant emittance identical to that of an unknown resource.

A thermocouple that is used in infrared spectroscopy to detect a sample's infrared emittance. See thermocouple.

That process by which radiation spontaneously emitted by a volume of optical materials is resonantly reabsorbed within the same volume before it escapes. This effect is manifested in a reduction in...

The film used in photographic dosimetry to record the types and amounts of ionizing radiation, such as x-rays and gamma rays, present in an area for a set interval of time. The negative produced by...

Plates of glass containing as many heavy metal oxides as can be dissolved in the glass without causing devitrification. The glass is yellow, very heavy and has a high refractive index. It is almost...

Electromagnetic radiation present upon the open aperture of the source within an operating environment.

Electromagnetic energy that is capable of producing photochemical activity.

Gamma ray radiation released when matter and antimatter, such as electron and positron, unite and eliminate each other, transforming completely into energy. The resulting gamma ray spectrum depends...

The high-speed electrons and positrons emitted by radioactive materials.

Radiation that occurs perpendicular to the plane of the radiation device.

The radiation produced when a charged particle traverses a medium that has a refractive index considerably greater than unity. The moving particle has a velocity that exceeds the velocity of light in...

Radiation in which the phase relationship between any two points in the radiation field has a constant difference, or is exactly the same in either the spatial or the temporal mode throughout the...

Category inclusive of all radiation that is incited electronically, except laser radiation, as a function of the application of laser power to a system.

Radiation in which every ray from any given object point can be considered to be parallel to every other. This is never completely the case: The light from a star is really diverging, and all...

Radiation emitted from vibrating charged particles. A combination of oscillating electrical and magnetic fields that propagates through otherwise empty space with the velocity of light. This constant...

Radiation that is emitted by a source outside the Earth and its atmosphere.

That radiation characterized by wavelengths ranging from 0.2 to 0.3 µm in the electromagnetic spectrum.

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

Any object that emits radiation of a wavelength lying between about 0.75 to 1000 µm. A calibrated secondary source usually is a heated cavity (blackbody) or a filament lamp rated in wattage...

Generally, any radiation that can form ions, either directly or indirectly, while traveling through a substance.

Application of radiation to an object.

The hydrogen-derived, ultraviolet radiation running from 1216 to 512 A, discovered by Theodore Lyman in 1914.

Radiation having waves that are out of phase in space and/or time.

Radiation that does not produce free electrons and ions, or electrically charged particles.

Irregular waves; e.g., light waves, having little coherence and a broad spectrum of frequencies.

The radiation emitted from a group of charged particles that does not depend on the temperature of the source in which those particles are generated.

Photosynthetically active radiation (PAR) is the 400- to 700-nm region (visible light) of the electromagnetic spectrum that is absorbed and used by the plant for photosynthesis. Also referred to as...

The formula describing the spectral radiant emittance of a perfect blackbody as a function of its temperature and the wavelength of the emitted radiation. where Wλ equals radiation...

Radiation used to excite an optical or laser material to a higher energy level. See optical pumping.

The radiation emitted in semiconductors when electrons in the conduction band recombine with holes in the valence band. If population inversion occurs between portions of the valence and conduction...

That radiation emitted by an atom or molecule that has the same frequency as that of an incident particle; e.g., a photon. It generally involves a transition to the lowest energy level of the atom or...

Characterizes the significant solar radiation at the surface of the earth, so named because its spectral range extends only from 0.3 to 2.8 µm.

Term applied to radiation composed of particles or photons that will not easily penetrate a material because of their low energy levels.

Solar radiation intensity existing in free space at the mean solar distance of the Earth. Commonly expressed in g cal cm-2min-1, the constant is equal to the amount of incident radiation -- in unit...

Radiation from the sun that is made up of a very wide range of wavelengths, from the long infrared to the short ultraviolet with its greatest intensity in the visible green at about 5000 Å. The...

The correlation of radiation between the phases of monochromatic radiation emanating from two separate points.

Radiation emitted by electrons when they travel in circular orbits at speeds close to that of light. Synchrotron radiation occurs in the x-ray and ultraviolet regions of the spectrum. Once considered...