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Photonics Dictionary: N

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NEA
negative-electron affinity; noise equivalent angle
near point of eye
The closest distance to which the eye can focus on an object, normally taken to be 250 mm. The near point varies with age.
near ultraviolet
The longest wavelengths of the ultraviolet region, nominally 300 to 400 nm.
near-field diffraction -> 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,...
near-field holography
A lithography method that allows the transfer of fine-pitch gratings from a phase mask into photoresist. The exposure takes place with the light coming under an oblique angle to the mask. The...
near-field region
The area closest to an aperture or source where the diffraction pattern differs substantially from that observed at an infinite distance, or more specifically, the far field. Also referred to as the...
near-field scanning optical microscope
A scanning probe microscope that analyzes the surface of a specimen by recording the intensity of light as it is focused through a pipette and raster scanned across the specimen at a distance less...
near-field scanning
A measurement technique used to determine the spatial distribution profile of an electrical or optical quantity of interest which is provided by multiple scans within the near-field region of a...
near-field walk
In a laser diode, lateral motion of the beam center at the facet when the drive current is changed.
near-infrared camera
A near-infrared (NIR) camera is an imaging device designed to capture images in the near-infrared region of the electromagnetic spectrum. The near-infrared spectrum typically extends from about 700...
near-infrared spectrometer
A near-infrared (NIR) spectrometer is an analytical instrument used to measure the absorption, transmission, or reflection of light in the near-infrared region of the electromagnetic spectrum....
near-infrared spectroscopy cerebral oximetry
A monitoring technique used to measure the oxygen saturation levels in the brains of patients, commonly in operating room and neonatal intensive care unit settings. The technique, which is based on...
near-infrared spectroscopy
Near-infrared spectroscopy (NIRS) is a non-invasive analytical technique that uses the near-infrared region of the electromagnetic spectrum to study the absorption of light by molecules in a sample....
near-infrared
The shortest wavelengths of the infrared region, nominally 0.75 to 3 µm.
near-ultraviolet light source
A light source, such as the sun or an incandescent lamp, that freely penetrates ordinary glass bulbs and emits in the near-ultraviolet (wavelengths ranging from about 300 to 400 nm). A mercury vapor...
nearest neighbor
A resampling and interpolation method that uses only the value of the nearest neighbor pixel, while not considering values from any other neighboring pixels from the source image to determine the...
NEB
noise equivalent bandwidth
NEC
national electric code
NEDT
noise equivalent delta temperature
NEE
noise equivalent energy; noise equivalent exposure
negative absorption
Amplification; the result of the excess of stimulated radiation over absorbed radiation.
negative carrier
The structure that holds the photographic negative in a proper position that is both flat and parallel to the lens plane, as well as being placed in a fixed position that is the right distance from...
negative crystal
A uniaxial, birefringent crystal such as calcite or ruby in which the velocity of the extraordinary ray surpasses that of the ordinary ray. This can also be defined as the index of refraction of the...
negative dielectric anisotropy
State typically studied in liquid crystals in which the dielectric coefficient parallel to the director is less than the dielectric coefficient perpendicular to the director.
negative ghost
A ghost image that has the reverse lightness relations of the original image. This phenomenon is a common optical illusion that takes place in the human visual system, following long exposures to an...
negative glow
In a cold-cathode tube, the luminance between the cathode dark space and the Faraday dark space. In a vacuum tube, the luminance between the Crookes dark space and the Faraday dark space.
negative lens -> diverging lens
A diverging lens is a type of lens that causes parallel rays of light to spread out or diverge. It is thinner in the center than at the edges and is commonly referred to as a concave lens. The most...
negative meniscus lens -> divergent-meniscus lens
A lens with one surface convex and the other concave, the latter having the greater curvature. It also is known as a diverging meniscus lens.
negative stereoscopic image
When a stereo pair of images is switched so that the right eye sees the left image and the left eye the right, the stereo image perceived will be reversed in terms of relative object depth.
negative temperature -> population inversion
The condition in which there are more atomic systems in the upper of two energy levels than in the lower, so stimulated emission will predominate over stimulated absorption. This condition may be...
negative-electron-affinity photocathode
A photocathode having a P-type semiconductor with a work function less than its bandgap. The photocathode can release a hundredfold increase of photoemission in the infrared region.
negative-refraction metamaterial
An artificial material, engineered to have a negative refractive index value, such that light or any other form of electromagnetic radiation bends in the opposite direction than it would in ordinary...
negatron
A negatively charged elementary particle. See electron.
NEI
noise equivalent irradiance
NEMA
National Electrical Manufacturers' Association
nematic phase
A form of liquid crystal with an appearance of moving, threadlike structures, particularly visible when observed in thick specimens with polarized light. During this phase, the molecules of the...
NEMS
nanoelectromechanical systems
neodymium glass
Glass containing small quantities of neodymium oxide that is used as a filter plate in color television or as a lasing medium (Nd:glass) in solid-state lasers.
neodymium:YAG
Literally, neodymium:yttrium-aluminum-garnet. A cylindrical rod of yttrium-aluminum-garnet doped with neodymium that is the active medium of the Nd:YAG laser, a highly serviceable solid-state device...
neon indicator tube
A cold-cathode tube containing neon and designed to visually determine a potential difference or field.
neon tube
An electron tube containing neon gas that uses the transmission of an electric current through the gas to ionize the neon and produce a luminous red discharge.
neoprene
A type of thermoset rubber used to jacket fiber optic cables, including those used in outdoor military installations.
NEP
noise equivalent power
Nernst glower
A Nernst glower, also known simply as a Nernst lamp or Nernst filament, is a type of incandescent lamp or radiant heater based on the Nernst effect. It was invented by the German physicist and...
Nernst light source -> Nernst glower
A Nernst glower, also known simply as a Nernst lamp or Nernst filament, is a type of incandescent lamp or radiant heater based on the Nernst effect. It was invented by the German physicist and...
NET
noise equivalent temperature
network interface card
A network interface card (NIC), also known as a network adapter or LAN adapter, is a hardware component that allows computers to connect to a local area network (LAN) and communicate with other...
neural network
A computing paradigm that attempts to process information in a manner similar to that of the brain; it differs from artificial intelligence in that it relies not on pre-programming but on the...
neuromorphic
Neuromorphic refers to the design and development of computing systems or devices that are inspired by the structure and functioning of the human brain and nervous system. The term is derived from...
neuromorphic vision sensor
A neuromorphic vision sensor is a type of imaging device designed to mimic the structure and functioning of the human visual system. Inspired by the biological principles of the human eye and brain,...

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