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Definitions: J

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jacket
The outer material that surrounds and protects the buffered and unbuffered fibers in an optical cable.
Jacquinot advantage
The higher throughput obtained with an FTIR device compared with traditional spectrometers that need slits to achieve resolution. The advantage differs according to wave number and resolution.
Jamin refractometer
An instrument designed to measure the index of refraction of a gas by the interference patterns formed by two beams, one of which passes through a vacuum tube in which the gas is slowly released.
Jansky noise
Phrase applied to any noise of extraterrestrial origin, named for the engineer who discovered the phenomenon.
jellet prism
A prism produced by severing a Nicol prism and reconstructing the polarization angles of the two halves so that they are slightly wedged toward each other.
jet-streamed dye laser
A continuous-wave dye laser that uses a circulation pump and nozzle to provide an optically flat stream of dye across the laser's optical axis.
jig
A device to hold and locate a workpiece as it guides, controls or limits a cutting tool.
jig allowance
Also called coating jig allowance. That margin on an optical component that is outside the clear aperture for use in holding the component in the optical thin-film coater tooling during the...
jig transit
An optical instrument containing a gimballed sighting telescope, used to measure angular relationships in horizontal and vertical planes.
jitter
1. In relation to cathode-ray tube displays, errors in the signal's amplitude, phase or both that result in small, rapid aberrations in size or position of the image. 2. Errors of synchronization...
Johansson geometry
A design for bent crystal monochromators in which spacing is constant along any circular arc terminating at the two foci and with equally spaced Bragg planes curved about only one axis.
Johnson's curve
The graph of a curve describing the spectral irradiance of extraterrestrial sunlight.
joint transform correlator
A device consisting of two optical systems in which two signals are simultaneously transformed to produce their spectra, and these spectra are multiplied and inversely transformed to produce the...
Josephson effect
Characteristic of radiation detectors that produce energy that is similar to the energy of superconductive gaps when interacting with photons.
joule
A unit of energy or work in the MKS system of units. One joule is equal to 107 ergs.
Joule-Thomson cooler
A detector cooling device in which a gas under high pressure escapes through an expansion valve in the tank; as the escaped gas liquefies, it cools the site of the sensor.
Judas optics
A small defocused Galilean telescope mounted in a hole in a door. Viewed from inside through the positive lens, a wide-angle view of the outside is seen; viewed from outside through the negative...
junction diode
A semiconductor device with the property of conducting current more easily in one direction than the other. It has two terminals containing a single crystal of semiconducting material that ranges...
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