Photonics Dictionary

Flow cytometry is a powerful technique used in biology and medicine for the quantitative analysis of the physical and chemical characteristics of cells and particles suspended in a fluid. The method...

A flowmeter is a device used to measure the flow rate or quantity of a fluid passing through a particular point in a system. It works by sensing the velocity of the fluid passing through it and...

A technique developed to measure the molecular weight of macromolecules by analyzing the spontaneous fluctuations that occur in the inherent thermodynamic concentration of solute molecules in a...

Fluence is a term used in various scientific and technical disciplines to describe the amount of something per unit area. The specific meaning of fluence can vary depending on the context in which it...

A powerful method, referred to as FCS, for determining the average diffusion coefficients of fluorescent molecules in solution or membranes. FCS measurements rely on recording the transition of...

A device, also called a fluorescence lifetime instrument, that measures decay curves of fluorescing samples. It generally consists of a gated pulsed flashlamp or a cavity dumped dye laser...

Fluorescence lifetime refers to the average time it takes for a fluorophore, a molecule that absorbs light at one wavelength and emits it at another, to return to its ground state after being excited...

Fluorescence lifetime imaging (FLIM) is an advanced imaging technique that provides information about the lifetime of fluorescence emissions from fluorophores within a sample. Unlike traditional...

An instrument used to measure the duration of fluorescence emanating from a biological sample to monitor and evaluate its condition.

The analysis and measurement of the fluorescence emitted by a source. Fluorometric processes are more sensitive than light absorption methods and are rapidly being applied in medical and biological...

Flux per unit area measured normal to the direction of propagation of the flux.

Time elapsed during the radiant output change from 10 to 90 percent of maximum in a light-emitting diode or laser. Usually expressed in nanoseconds and measured from the moment of onset of the...

FMCW lidar stands for frequency-modulated continuous wave lidar. It is a type of lidar (light detection and ranging) technology used for remote sensing, distance measurement, and 3D mapping. FMCW...

The focal length of a lens is the distance between the lens's optical center (or principal point) and the image sensor or film when the lens is focused at infinity. In simple terms, it is the...

In a symmetrical optical system this is a measure of the influence of the system upon the focus of a pencil of rays passing through it.

A device used to measure the focal length of an optical system or lens.

Frame rate refers to the frequency at which consecutive images, or frames, are displayed in a video sequence. It is typically measured in frames per second (fps) and determines the smoothness and...

A frequency comb is a precise and regular series of equally spaced spectral lines, or frequencies, that are generated with great accuracy. The term "frequency comb" is often associated with the Nobel...

In a lens, the square of the radius of its aperture divided by the product of the focal length and the wavelength. It measures the importance of diffraction in the image formed by the lens. A small...

FTIR (Fourier transform infrared) spectrometer is a powerful analytical instrument used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas sample. It operates based...

The full width at half maximum (FWHM) is a measure used in various fields, particularly in spectroscopy, signal processing, and imaging, to characterize the width or extent of a distribution, peak,...

Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that measures changes in hemoglobin concentration in the brain. It utilizes near-infrared light to penetrate the...

A galvanometer is an instrument used for detecting and measuring small electric currents. It typically consists of a coil of wire suspended in a magnetic field, with a pointer attached to the coil....

An instrument used to detect and measure the energy distribution of gamma rays. It has been used to chart the radioactivity at the lunar surface.

A photometer used to measure sky brightness and polarization associated with zodiacal light, background starlight, F-region airglow and spacecraft corona.

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...

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 device that detects and measures the quantity of exposure to nuclear radiation. It uses a special glass rod that fluoresces when placed under ultraviolet radiation after its exposure to nuclear...

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 spectrometer or autocollimator used to measure prism angles.

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

An instrument capable of precise measurements of the Earth's gravity. This permits the detection of small changes in local height that indicate changes in the Earth's crust and subsurface density.

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...

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...

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,...

A test for spherical aberration, coma or astigmatism in which incident rays from a point source are isolated by small holes in a metal disc located close to the lens or mirror under test....

A gas lamp used in the early 1900s as a physical standard for measurement of luminous intensity. The Hefner unit was superseded by the candle and then by the candela.

A display that allows the observation and measurement of the altitude and range of airborne objects.

The capability of the spatial distributions of incident and reflected flux to interchange completely without alteration of the measured reflectance.

A photoanalytical instrument for analysis of jaundice conditions in infants that measures bilirubin (a breakdown product of hemoglobin that produces jaundice), albumen-carrying capacity and binding...

Light measurement by comparison of the luminances of unlike chromaticities.

A high-speed motion camera, also known as a high-speed camera or slow-motion camera, is a specialized imaging device designed to capture fast-moving events or phenomena at extremely high frame rates....

Hyperchromic shift refers to an increase in the absorption of light, leading to a higher absorbance, often observed in certain chemical or biological substances upon undergoing a structural change....

Hyperspectral resolution refers to the level of detail or granularity in the spectral information captured by a hyperspectral imaging system. In hyperspectral imaging, the electromagnetic spectrum is...

A photometric instrument used to measure the illumination falling on a surface. It may be photoelectric or visual.

A measure of the closeness with which an optical image is capable of resembling the original object. The factors that affect image quality are lens aberrations, diffraction, dirt and stray light...