Photonics Dictionary: F

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...

With respect to a unit cell in a crystal structure, the property defining an atom located at the center of each face.

The diffraction pattern of a source such as a light-emitting diode, injection laser diode or the output end of an optical waveguide observed at an infinite distance from the source.

A system designed to control the output quantity of a device by returning a portion of its output signal to its input. This results in the manipulation of the input quantity so that the desired...

In microscopy, the measured distance between theoretical parallel lines that are drawn tangent to the particle profile and perpendicular to the ocular scale.

The Fermi liquid state refers to a specific state of matter in quantum mechanics, particularly describing the behavior of interacting fermions (particles with half-integer spin, such as electrons) at...

Ferroelectric materials are a type of dielectric materials that exhibit spontaneous electric polarization, meaning they possess a permanent electric dipole moment even in the absence of an external...

The law stating that the critical fusion frequency is approximately proportional to the logarithm of the luminance and the area.

A standard for fiber optic data transmission systems being developed by the American National Standards Institute (ANSI) and associated working groups that will make fiber optic components from...

A plate made up of thousands of glass fibers arranged parallel to one another, i.e., in a coherent bundle, and fused together so that it is hermetically tight. It transfers an image from one plane to...

A plate consisting of fused optical fibers with both surfaces ground and polished, and having the entrance surface curved to match the image curvature of the input lens system. The plate transmits to...

A fiber optic spectrometer is a device used for measuring the spectral content of light. It utilizes optical fibers to transmit light from a source to a spectrometer unit, where the light is...

A fiber-coupled photoconductive antenna (FCPA) is a type of optoelectronic device that combines a photoconductive antenna with optical fibers for the purpose of generating or detecting terahertz...

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...

A photodetector employing photoregeneration of carriers in the channel region of an FET structure to provide photodetection with current gain.

Intensity of emission as a function of direction in a given plane.

The number of fields scanned per second in a television system. The US standard is 60. Also called field frequency.

A mechanism in a camera designed to position the film in the focal plane for exposure.

1. With respect to radiation, a device used to attenuate particular wavelengths or frequencies while passing others with relatively no change. 2. See digital filter.

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

A grating used as a reflectance filter, particularly in the far-infrared. Small plane gratings, blazed for the wavelength of the unwanted radiation, are produced for this purpose.

A function used in a convolution filtering operation. The image to be filtered is convolved with the filtering kernel to obtain the enhanced image.

A spectrophotometer that makes use of filters to isolate narrow bands of the spectrum.

A device that holds a number of filters and allows the filter with the desired characteristics to be rotated into an optical aperture.

A finite version of Shannon's sampling theorem that states that a class of functions can be reconstructed exactly by a sufficient number of spectral samples; the reconstructed function is an explicit...

Fixed-pattern noise is the measure of the static (nontemporal) differences between pixels when the detector is evenly illuminated. In microbolometers, this effect is mostly caused by mismatch between...

A type of interferometer noted for producing narrow multiple-beam interference fringes. As a result, when compared with the Twyman-Green, the Fizeau interferometer has fewer optical components, does...

Any of a number of instruments that uses a flame to vaporize a solution of the chemical being analyzed so that light may be passed through the vapor. Monochromation of the transmitted light is...

A filter, partially opaque to near-ultraviolet, visible and infrared radiation, that may be made by exposing and processing photographic film. Such materials are almost equally opaque to radiation of...

A sensitometer that utilizes an electronic flashtube or a photoflash lamp as both the light source and the shutter for obtaining short-duration exposures.

A bench photometer that depends on the inability of the eye to distinguish color in brief flashes of light. Any difference in the intensity of reflected colored samples, presented to the observer in...

The Floquet Fermi liquid state refers to a concept in condensed matter physics that arises when a system is subjected to periodic driving or modulation, typically by an external periodic field such...

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 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...

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...

Agents used for testing light sources and natural daylight with visual and instrumental assessment using a set of white metameric pairs.

The optical form of the crystal fluorspar, calcium fluoride, that is utilized for its low optical dispersion, its low refractive index, and its transparency to infrared and ultraviolet radiation.

An objective that uses the mineral fluorite in its construction to reduce the secondary spectrum. It is usually intermediate between achromatic and apochromatic in correction, but may be more highly...

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

A special laser glass made primarily of fluoride compounds that exhibits extremely low refractive index and allows greater levels of energy to be generated as the laser beam passes through the...

A form of image intensifier designed to amplify a weak fluoroscopic image. The image is received at an input phosphor screen, as opposed to the light-sensitive electrode emitter used in regular image...

A highly stable heavy-metal fluoride glass made from the fluorides of zirconium, barium, lanthanum, aluminum and sodium.

A shutter having one or more roller blinds of material with a variable slit that moves across the back of the camera when released and exposes the sensitized material progressively.

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

A single-particle scattering technique in which an incident laser beam is tightly focused by means of lenses to yield a focal spot in the scattering material with a diameter on the order of the...

A salt of formic acid that can be used to enhance the photosensitivity of silver halide crystals.