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8,236 terms
Photonics Dictionary
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flyback
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.
flying spot
The moving spot of light emitted by a source, generally a cathode-ray tube, to illuminate specific points of an area carrying light and dark regions according to a specific pattern.
flying spot microscope
A microscope that uses a flying spot scanner, directed through the eyepiece, as a light source to determine the features of a transparent specimen. The flying spot is modulated by the varying density...
flying spot scanner
A device used to scan, with a small, intensely bright spot, portions of a picture surface and to transform the original picture into a series of electrical signals. In optical character recognition,...
fm
femtometer
FM
frequency modulation
FM-SC
frequency-modulated subcarrier
FMCW
frequency-modulated continuous wave
FMCW lidar
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...
FO
fiber optic
focal collimator
A collimator having, at one end of a tube, an objective lens, and at the other, a reticle with a pair of spaced lines located accurately in its focal plane. It is generally useful as an apparatus for...
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...
focal plane array
A linear or two-dimensional matrix of individual detector elements, typically used at the focus of an imaging system.
focal plane assembly
An infrared imaging device composed of a detector array and readout electronics. It may include a cryogenic cooling system. The assemblies are used in meteorological and surveillance satellites,...
focal plane shutter
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.
focal plane
A plane (through the focal point) at right angles to the principal axis of a lens or mirror; that surface on which the best image is formed.
focal point
That point on the optical axis of a lens, to which an incident bundle of parallel light rays will converge.
focal power
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.
focometer
A device used to measure the focal length of an optical system or lens.
FOCT
fiber optic current transformer
focus
1. The focal point. 2. To adjust the eyepiece or objective of a telescope so that the image is clearly seen by the observer. 3. To adjust the camera lens, plate, or film holder so that the image is...
focus control
1. A mechanism that permits the focusing of an optical system.2. A means of obtaining the sharpest image from a cathode-ray tube display by adjusting the size of the spot where it reaches the screen.
focus lamp
An incandescent or carbon arc lamp designed with a stable and compact arc or filament that permits it to be used as a light source to be focused by a lens system.
focused laser scattering
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...
focusing anode
One of the electrodes used to focus the electron beam of a cathode-ray tube. As the electrode's voltage is changed, its electrical field is changed, resulting in a change of the electron beam's spot...
focusing coil
A coil used to focus an electron beam by the generation of a magnetic field parallel to the beam.
focusing corner cube
A retroreflector that can focus a beam of light, with one planar reflective surface, one spherical and a third that is either planar or convex cylindrical.
focusing scale
A scale on an optical instrument that indicates the condition of focus. May indicate the distance to the object or diopter output, or from infinity focus.
fog
1. A term used to describe the clouded appearance of an incompletely polished surface that scatters light. 2. The accumulation of moisture on an optical surface. 3. The extra spectral blackening of a...
FOG
fiber optic gyroscope
FOG-M
fiber optic guided missile
FOIRL
fiber optic inter-repeater link
fold
1. A flaw in a blank caused by folding the blank's surface during its formation. 2. The change in the direction of a system's optical axis caused by a reflective component.
footcandle
Unit of illuminance equal to one lumen per square foot. (fc).
footlambert
Unit of luminance equal to 1/p candela per square foot. (fl).
footprint
1. The sector of the Earth's surface registered upon a remote sensing device in a satellite. 2. The amount of space occupied by a component on the surface upon which it is mounted. 3. The space on an...
Forbush decrease
Decrease in cosmic ray activity that is observed approximately 24 hours after a solar flare, attributed to a shielding effect produced by magnetic fields contained in the plasma of the cloud emitted...
forensic photography
The application of ultraviolet, x-ray, infrared and conventional photography to law enforcement.
FORJ
fiber optic rotary joint
formate
A salt of formic acid that can be used to enhance the photosensitivity of silver halide crystals.
Förster resonance energy transfer
Förster resonance energy transfer (FRET) is a mechanism describing the transfer of energy between two closely spaced fluorescent molecules. This phenomenon is named after the German scientist...
forward bias
Voltage that produces current flow in the direction of lesser resistance to the steady-state direct current, i.e., from the anode to the cathode.
forward-looking infrared
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...
FOTP
fiber optic test procedure
FOTS
fiber optic transmission system
Foucault chart
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resolution target
A chart on paper or glass containing a series of sets of lines at progressively smaller spacing and used to ascertain the limiting number of lines per millimeter that an optical system is capable of...
Foucault knife-edge test
The Foucault test is performed by moving a knife edge laterally into the image of a small point source. The eye, or a camera, is placed immediately behind the knife edge, and the exit pupil of the...
Foucault prism
A polarizing prism formed from calcite that is like the Nicol prism but has the two parts divided by a thin air-film and cut to such angles that the extraordinary beam will be transmitted and the...
Foucault rotating mirror
A rotating mirror coupled with a distant mirror and used in a system by Foucault to compute the velocity of light. Light moving from the rotating mirror to the distant mirror and back was following...
four-level laser
A solid-state laser consisting of active atoms or ions of a transition metal, rare-earth metal or actinide, imbedded in a crystal or glass material, often garnet. Excitation and transfer to different...
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Photonics Dictionary
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