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Photonics Dictionary: N

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neutral density coating
A coating applied to a neutral density glass that is designed to reduce the amount of light evenly across the transmitted light spectrum with no color distortion. These coatings are designed to...
neutral density filter
A light filter that equally decreases the intensity of all wavelengths of light without altering the relative spectral distribution of the energy.
neutral density wedge
A strip or annulus of glass coated with a semitransparent material such as inconel. The coating thickness, and as a result its transmission, varies linearly as a function of distance. The neutral...
neutral mixture
An additive color mixture that appears to have no hue.
neutralization
In optics, the process of combining two lenses having equal and opposite powers to produce a result having no power.
neutron drip line
Prediction based on observations of nuclear masses in the valley of stability that indicates the maximum number of electrons that will bind with a given number of protons in progressive order along...
neutron radiography
The nondestructive analysis and recording of industrial components based on the absorption of relatively low-energy neutrons by material having low atomic numbers. The visible image formed by the...
NEWS
north, east, west, south
newton (N)
The unit of force in the mks system that will give 1 kg of mass an acceleration of 1 m/s2.
Newton's rings
The series of rings or bands formed when light beams reflected from two polished, adjacent surfaces, placed together with a thin film of air between them, interfere. By counting these bands from the...
Newtonian telescope
A telescope with a concave paraboloidal objective mirror and a small plane (diagonal) mirror that reflects rays from the primary mirror laterally outside the tube where the image is viewed with an...
NEXT
near-end crosstalk
nF
nanofarad
NHZ
nominal hazard zone
Nichols radiometer
An instrument devised by Nichols and Hull for use in the measurement of radiation pressure. The device has two small silvered, glass mirrors that are suspended, in the way of a torsion balance, by a...
Nicol prism
A prism invented by William Nicol in 1828 that is made of calcite, the end faces of which are ground to an angle of 68° between one vertical side and the end surface. The prism is cut diagonally...
night-vision device
A device that uses low-level visible radiation or infrared radiation to produce a visual image of a night scene. These devices may rely on the amplification of existing visible light by...
Nipkow disc scanner
A device consisting of a disc with a spiral arrangement of holes that is used to convert visible patterns into electrical patterns. Light is reflected from the subject and focused through a vertical...
NIR
near infrared
NIST
National Institute of Standards and Technology
nit
Unit of measurement of brightness (luminance) equal to one candela per square meter.
nitric oxide detector
A pollution-measuring device used to detect the presence of nitric oxide regardless of other gases present. It utilizes the principle of laser magnetic resonance (LMR).
nitrogen vacancy
A nitrogen vacancy (NV) refers to a specific type of defect or impurity in a crystal lattice where a nitrogen atom replaces a carbon atom adjacent to a vacancy (an empty lattice site) in the diamond...
NLC
nematic liquid crystal
NLLS
nonlinear least square
NLO
nonlinear optics
NLOS
nonline-of-sight
nm
nanometer
Nm
Newton meter
NMOS
N-type metal-oxide semiconductor
NMR
nuclear magnetic resonance
NN
neural network; nearest neighbor
NO
nitric oxide
NOAA
National Oceanic and Atmospheric Administration
noble gas
A monatomic, chemically inert gas such as argon, neon, krypton and xenon.
noctovision
A television system used for seeing in the dark, particularly with the use of infrared rays.
NOD
night observation device
nodal bench
A bench with instrumentation including a collimator, a microscope, positioners and a nodal slide used to rotate a lens about its second nodal point. The nodal bench is used to determine the cardinal...
nodal points
Of all the rays passing through a lens from an off-axis object point to its corresponding image point, there is always one ray whose direction in the image space is equal to that in the object space....
nodal testing
The measurement of first- and higher order properties of a lens and its formed image, including effective focal length, back focal length, f number, aberrations, blur patterns, magnification and...
node
In a communications network, a point at which data are received or from which they are sent. Though the term often is used synonymously with workstation, interconnection points in a network also are...
NOHD
nominal ocular hazard distance
noise
The unwanted and unpredictable fluctuations that distort a received signal and hence tend to obscure the desired message. Noise disturbances, which may be generated in the devices of a communications...
noise current
Any noise or current fluctuation that prevents precise measurement of the signal current. Both dark current and signal current have random fluctuations that affect the arrival of pulses. Thermal...
noise equivalent delta temperature
In a thermal imaging system, the change in temperature that yields a signal-to-noise ratio of unity.
noise equivalent irradiance
The amount of spatial noise detected equivalent to the output emission location of the giving source.
noise equivalent power
At a given modulation frequency, wavelength, and for a given effective noise bandwidth, the radiant power that produces a signal-to-noise ratio of 1 at the output of a given detector.
Nomarski microscopy
Also referred to as differential interference contrast (DIC) microscopy; Nomarski microscopy is a unique form of microscopy especially suited for the evaluation of surface quality and defects as well...
nominal hazard zone
Zone of laser operation in which the direct, reflected or scattered light exceeds the laser's MPE and (by ANSI standards) requires the use of protective eyewear.
nominal ocular hazard distance
The calculated normal distance from a photon source at which harmful interaction with the incident light will occur. Interaction distance produces the effect of MPE (Maximum Permissable Exposure) on...

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