Definitions

The term applied to the geometrical structure of radiometry or of the propagation of any quantity that is conversed and that travels in straight lines at velocities characteristic of the medium.

A phonon is a quantum of vibrational energy associated with the periodic motion of atoms or molecules in a crystalline lattice. In simpler terms, phonons are quanta of lattice vibrations in a solid...

A type of glass that includes phosphorus pentoxide and that, unlike silica-based glass, is resistant to hydrofluoric acid.

A chemical substance that exhibits fluorescence when excited by ultraviolet radiation, x-rays or an electron beam. The amount of visible light is proportional to the amount of excitation energy. If...

Very small phosphor particles present on the screen of a picture tube.

A source made to glow by electrons that are produced either electrically or by isotopes of various elements.

The property of a phosphor that determines its ability to emit light for a time after the stimulus has been extinguished. Persistence may extend to over a minute.

A method for remote measurement of the temperature of moving surfaces in harsh environments by using a laser to stimulate fluorescence of thermographic phosphors and then measuring the decay times by...

Luminescence is the emission of light from a source that is delayed by more than 10-8 s following excitation.

The spectroscopic study of the radiation emitted by the lifetime of phosphorescence.

A process used in pyrometry and photothermometry to create a photographic record of a surface's temperature gradients. Essentially, it involves the exposure of a glowing phosphorescent surface to the...

Periodic interruptions of a light beam incident on an absorbing medium that produce heat, expansion and acoustic wave generation. Since the amplitude of this wave is proportional to the absorbed...

A device for measuring absorption coefficients in which a confined, nonabsorbing gas fills the space inside the cell between the two windows, which are made from a weakly absorbing medium.

Abbreviated PAI. An imaging modality with a hybrid technique based on the acoustic detection of optical absorption from endogenous chromophores or exogenous contrast agents. Light is absorbed by the...

A method for obtaining the optical absorption spectra of solids, semisolids, liquids and gases. PAS is inherently insensitive to reflection or scattering from the sample, analyzes opaque samples and...

Photoacoustic refers to the generation of acoustic (sound) waves following the absorption of light (usually laser pulses) by a material. This phenomenon occurs when light energy is absorbed by a...

A light therapy that utilizes nonionizing light sources, including lasers, LEDs, and broadband light, in the visible and infrared spectrum. It is a nonthermal process involving endogenous...

Photobleaching is a phenomenon in which the fluorescence of a fluorophore (a fluorescent molecule or dye) is permanently reduced or eliminated upon prolonged exposure to light. This process occurs...

The responsivity of a photocathode to luminous energy equal to the ratio of the photoelectric emission to the incident luminous flux.

Photocathodes are specialized materials or surfaces that exhibit the photoelectric effect, wherein the absorption of photons leads to the emission of electrons. When photons with sufficient energy...

The term photochemical pertains to chemical processes or reactions that are initiated or influenced by the absorption of light. Photochemical reactions involve the interaction of light, often in the...

An instrument used to detect and measure radiant energy by the formation of a chemical reaction.

A method of producing disks for erasable optical data storage. Information is recorded by a laser beam that generates pits on the surface of the disk while it is being cryogenically cooled. Erasure...

The study of chemical reactions stimulated by the properties of light.

A chemical compound that exhibits a reversible change in its absorption spectrum upon irradiation with given wavelengths of light.

The discrepancy between the absolute luminance threshold and the photochromatic threshold.

Photochromic refers to a property exhibited by certain materials, typically organic compounds or dyes, which undergo reversible changes in color when exposed to light. Specifically, photochromic...

The reversible change in the absorption spectrum of certain compounds upon irradiation with a given wavelength of light.

A photographic recording instrument that measures deviation from the vertical of a drilled well or mine.

An optical medical instrument that uses an intense, precisely focused beam of light to stop weakened blood vessels from hemorrhaging. The thermal effect of the beam strengthens the weakened vessels...

Photoconductive antenna (PCA) is a semiconductor element that generates or detects high-frequency electromagnetic signals. Compact PCAs based on gallium arsenide (GaAs) or indium gallium arsenide...

A device for detecting visual and infrared radiation using a photoconductor as the principle sensing element.

The alteration of electric conductivity produced by the absorption of varying amounts of radiation composed of photons.

A film of material that exhibits varying conductivity based upon its absorption of varying amounts of photon radiation.

The conductivity increase exhibited by some nonmetallic materials, resulting from the free carriers generated when photon energy is absorbed in electronic transitions. The rate at which free carriers...

Material used to integrate photoconductors into electro-optical systems. It should provide low resistance to the flow of charge, avoid recombination of the charge carriers, inject only majority...

A light-sensitive resistor in which resistance decreases with increase in light intensity when illuminated. The device consists of a thin single-crystal or polycrystalline film of compound...

The current that flows through a photosensitive device, such as a photodiode, as the result of exposure to radiant power.

The effect that the optical losses in a medium can grow when the medium is irradiated with light at certain wavelengths.

A Darlington current amplifier consisting of two separate transistors, of which a phototransistor is the input device.

A photodetector, also known as a photosensor or photodiode, is a device that detects and converts light into an electrical signal. Photodetectors are widely used in various applications, ranging from...

The effect, present in particular phosphors, that is defined as a transformation in the dielectric constant of a material when illuminated.

The potential difference between two areas of a semiconductor when one is exposed to light.

A photodiode detector is a semiconductor device that converts light into an electrical current. It operates based on the principle of the photoelectric effect, where photons of light incident on the...

A two-electrode, radiation-sensitive junction formed in a semiconductor material in which the reverse current varies with illumination. Photodiodes are used for the detection of optical power and for...

A spectroscopic process that detects and analyzes the discharge from an extrinsic surface with less than bandgap light. This method may determine the extrinsic surface-state energy levels of a...