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5,268 terms
Photonics Dictionary
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fovea
The central portion of the retina that has the greatest sensitivity to form and color.
foveal vision
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photopic vision
Vision by means of retinal cones; color vision. Relatively high levels of luminance are required for photopic vision.
fractional photothermolysis
A laser skin-resurfacing method that creates microscopic thermal wounds referred to as microscopic treatment zones (MTZs), which are surrounded by uninjured tissue. The MTZs are usually arranged in a...
frame
1. To center an image or place it in any part of the television screen desired. Also applies to stills. 2. A single image of the connected multiple images on motion-picture film. 3. The size of the...
frame frequency
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 grabber
A frame grabber is a hardware device or interface card that connects to a computer or imaging system and is designed to capture and digitize frames of video or images from a video source such as a...
frame rate
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...
framer
A device that permits the adjustment of facsimile transmitters and recorders so that their scanning lines stop and start at the same place in relation to the subject copy.
frames per second
The number of separate images exposed by a cine camera in a second or the number illuminated by a cine projector in a second. By varying the number of images recorded per second, films can be created...
Franck-Condon principle
The principle that electronic energy transitions occur at such speeds that the nuclei of the atoms in the molecular system remain stable during the transfers.
Franz-Keldysh effect
Observed lengthening in wavelengths of the optical absorption edge of a semiconductor with the application of an electric field.
Fraunhofer diffraction pattern
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far-field diffraction pattern
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.
Fraunhofer hologram
A far-field pattern holographically reproduced image that is categorically considered with three-dimensional lensless photographs.
Fraunhofer lines
The dark absorption lines observed in the spectrum of the photosphere of the sun. There are thousands of these lines, the most prominent of which were observed and named by Fraunhofer early in the...
free radicals
Short-lived molecular or atomic particles, with an unpaired electron, that play an important part in many photochemical reactions.
free-carrier absorption
The phenomenon whereby an electron within a band absorbs radiation by transferring from a low-energy level to an empty high-energy level.
free-carrier photoconductivity
Photoconductivity that may be extended as far as the microwave region because of the absorption of photons by electrons.
free-electron laser
A free-electron laser (FEL) is a type of laser that generates coherent, high-intensity electromagnetic radiation by using a beam of accelerated electrons as the lasing medium. Unlike traditional...
free-space optical interconnect
A type of internal photonic connection in an integrated circuit in which a holographic grating is used to focus light at points on a silicon chip, maximizing the speed of signal propagation.
free-space optics
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...
free-spectral range
The frequency space between consecutive transmission peaks in the transmission spectrum of a Fabry-Perot interferometer or etalon. The free-spectral range is inversely proportional to the distance...
freeform mirrors
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
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...
Frenkel defect
A crystal defect that is a combination of a vacancy and an interstitial created by the removal of an ion from a lattice and its placement in an interstitial position.
frequency comb
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...
frequency division multiplexing
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wavelength division multiplexing
A system that allows the transmission of more than one signal over a common path, by assigning each signal a different frequency band. Also known as frequency division multiplexing.
frequency domain
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...
frequency multiplication
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harmonic generation
Harmonic generation refers to a nonlinear optical process in which incoming photons interact with a material and produce new photons at integer multiples of the frequency of the incoming photons....
frequency response
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transfer function
The complex function, H(f), equal to the ratio of the output to input of the device as a function of frequency. The amplitude and phase responses are, respectively, the magnitude of H(f) and the...
frequency shift keying
In digital data transmission, the separation of the two binary states into output at two frequencies.
frequency
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.
Fresnel diffraction
1. Also known as near-field diffraction. The field of radiation sent through an aperture in an absorbing screen at large distances as compared with the wavelength and the dimensions of the aperture,...
Fresnel fringe
A single band in a group of light and dark bands that can be viewed in the periphery of Fresnel diffraction shadow.
Fresnel lens
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...
Fresnel loss
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Fresnel reflection loss
Reflection losses incurred at input and output of optical elements because of the difference in refractive index between glass and the immersion medium.
Fresnel mirrors
Two plane mirrors that are not wholly located in the same plane. When light from a point source or slit reflects from the two mirrors, interference bands are revealed in the region where the light...
Fresnel number
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...
Fresnel reflection
Fresnel reflection refers to the reflection of light at the interface between two different media with different refractive indices. This phenomenon was named after the French engineer and physicist...
Fresnel reflection loss
Reflection losses incurred at input and output of optical elements because of the difference in refractive index between glass and the immersion medium.
Fresnel reflection method
A method for measuring the index profile of an optical fiber by measuring the reflectance as a function of position on the end face.
Fresnel rhomb
A type of quarter-wave retarder in the form of a glass rhomb; light entering the retarder undergoes two total internal reflections, producing a change in phase.
Fresnel zone plate
A zone plate in which the zones are alternately transparent and opaque to specific radiation, and coarse enough so that no appreciable diffraction or focusing takes place. The Fresnel zone plate is...
Fried length
The length of the small space within which the atmosphere exhibits coherence, particularly in relation to an observer on Earth viewing celestial objects. The turbulence of the Earth's atmosphere...
Fried's seeing parameter
A calculated function that can be achieved experimentally with interferometric analysis of complex atmospheric altitude; expressed as a relation to the turbulence integrated over the entire...
fringes of superposition
The multiple beam form of Brewster's fringes formed when the two plane-parallel plates have high-reflecting surfaces.
front focal length
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focal length
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...
front porch
In communcations and video signals, the portion of a composite signal between the leading edge of the horizontal blanking pulse and the leading edge of the horizontal synchronization pulse.
frustrated total reflection
Light leakage at a total reflecting interface when another highly refractive medium is brought close to it.
FTIR
Fourier transform infrared; frustrated total internal reflection
FTIR spectrometer
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...
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Photonics Dictionary
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