Photonics Dictionary: F

Measurement of the interval during which a photodetector's signal and output current drops from 90 to 10 percent.

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...

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...

A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth...

The signal-to-noise ratio (SNR) obtained with a Fourier transform spectrometer when detector noise prevails, which exceeds the SNR of a scanning spectrometer in the same time by a factor proportional...

A femtosecond laser is a type of laser that emits ultrashort pulses of light with durations on the order of femtoseconds, where one femtosecond is equal to 10-15 seconds. These lasers are capable of...

The principle that a light ray extending from one point to another will, after any number of reflections and refractions, follow the path requiring the least transit time. This is also known as the...

A fiber laser is a type of laser in which the active gain medium is an optical fiber doped with rare-earth ions such as erbium, ytterbium, or neodymium. Fiber lasers generate coherent light through...

A fiber optic cable assembly refers to a complete unit consisting of optical fibers, connectors, protective jackets, and other components that are assembled together to facilitate the transmission of...

A fiber optic gyroscope (FOG) is a type of gyroscope that uses the interference of light waves to detect changes in orientation or rotation. It operates based on the principle of the Sagnac effect,...

A fiber optic preform is a cylindrical glass rod or tube used as the starting material for manufacturing optical fibers. It serves as the precursor from which optical fibers are drawn. The process of...

A wide-field multiobject spectroscopy system used in astronomy, in which a bundle of low-loss optical fibers positioned on the target images is rearranged at its other end into a linear array along...

The necessary increase of a photograph's exposure time as the result of the additional absorption of light by the filter being used.

Flow chemistry, also known as continuous-flow chemistry, is a chemical manufacturing process where reactions take place in a continuous stream of fluids (liquids or gases) rather than in batch...

Fluorescence is a type of luminescence, which is the emission of light by a substance that has absorbed light or other electromagnetic radiation. Specifically, fluorescence involves the absorption of...

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...

The photographic recording of a subject that exhibits luminescence only for an extremely short time (10-8 s) after the exciting source is removed. In the process, the subject may be illuminated by...

The suppression of fluorescence by absorption of the stimulating radiation.

Fluorescent proteins are proteins that exhibit the property of fluorescence, which is the ability to absorb light at a specific wavelength and emit light at a longer wavelength. These proteins are...

Time rate of flow of energy; the radiant or luminous power in a beam.

The time it takes a cathode-ray tube's electron beam to return to its starting point after completing one line, one field or one trace.

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...

A night-vision device that uses one or more infrared transducers to scan a scene in the 3- to 5-µm or 8- to 12-µm spectral region, convert the infrared radiation to electronic data and...

The number of times per second that the frame of a television system is completely scanned. In the United States, 30 per second is the standard frame frequency.

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...

Free-space optics (FSO), also known as optical wireless communication or optical wireless networking, refers to the transmission of data using modulated beams of light through free space (air or a...

Freeform mirrors refer to reflective optical components that deviate from traditional symmetric or rotationally symmetric shapes, such as spheres or paraboloids. Unlike conventional mirrors, which...

Freeform optics refers to the design and fabrication of optical surfaces that do not follow traditional symmetric shapes, such as spheres or aspheres. Unlike standard optical components with...

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...

The frequency domain is a concept used in signal processing and analysis to represent signals and data in terms of their frequency components. In contrast to the time domain, where signals are...

With reference to electromagnetic radiation, the number of crests of waves that pass a fixed point in a given unit of time, in light or other wave motion. Expressed in hertz or cycles per second.

A Fresnel lens is a type of optical lens that consists of a series of concentric grooves or steps carved into a flat, thin piece of transparent material, typically plastic or glass. This design...

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...

Functional materials refer to materials that possess specific properties or functionalities that make them suitable for particular applications or purposes. These materials are designed and...

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...

1. The combination of the effects of two or more stimuli in any given sense to form a single sensation. With respect to vision, the perception of continuous illumination formed by the rapid...

Fusion ignition refers to the point in a controlled nuclear fusion reaction where the energy released by the fusion reactions becomes self-sustaining, leading to a continuous release of energy...