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Photonics Dictionary: S

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structural character recognition
An approach to character recognition based on the structure of the character to be identified (number of straight lines, bays, holes, etc.); used where simple matching is not viable, as in...
structural color
Structural color refers to coloration in materials that is not caused by pigments or dyes but is instead a result of the physical structure of the material. In structural color, the interaction of...
structure function
The mean square difference in a spatial parameter at points spaced a given distance.
structured illumination microscopy
Structured illumination microscopy (SIM) is an advanced optical imaging technique used in microscopy to enhance the resolution of images beyond the diffraction limit imposed by traditional light...
structured light
The projection of a plane or grid pattern of light onto an object. It can be used for the determination of three-dimensional characteristics of the object from the observed deflections that result.
structuring element
The pattern used as a probe in morphological image processing to manipulate the size and shape of objects in an image.
STS
stimulated thermal scattering
Sturm interval
The distance between two focal lines in an astigmatic image produced by a lens or mirror.
stylus indicator alignment
A method used in surface quality testing for accurate positioning and rotation of metal spheres about an axis or fixed point in space that involves a sliding contact between the indicator and tip and...
stylus profilometer
A measuring instrument used for surface profiling and quantifying the roughness of a material. The stylus is placed on the surface of the material at a given contact force, then is moved laterally...
styrene acrylonitrile
A copolymer of styrene and acrylic used in molded optical components; it has a high refractive index and a low coefficient of thermal expansion.
subscriber loop
That portion of the telecommunications network that runs from a local central telephone to the subscriber premises.
substage condenser
In a microscope, the optical assembly that focuses light on the specimen and into the objective.
substrate
A substrate refers to a material or surface upon which another material or process is applied or deposited. In various fields, such as electronics, biology, chemistry, and manufacturing, the term...
subtractive color process
The basic process of color photography whereby colors are subtracted from white light by means of filters, making all colors and intensities available.
subtractive colors
Cyan, magenta and yellow. They are called subtractive because they each subtract one color by absorbtion and reflect the two others of the red, green, blue color primaries. Cyan absorbs red, magenta...
Suits' model
Family of deterministic models of plant canopy reflectance that provides deterministic formulation for each necessary parameter and a method to calculate reflectance as a function of sun and observer...
sum of slopes
Heat loss determined by the sum of rising and falling slopes at a constant temperature.
sun synchronous
Characterizes an Earth-orbiting satellite whose orbit plane is near polar and positioned at an altitude that allows it to pass over every spot on the Earth at identical local sun time twice a day.
sun-tracking concentrator
Controlled beam technology that introduces beams of sunlight through holes in a roof that are relayed throughout the building by a series of mirrors and lenses. Ideally, cool lighting is obtained by...
sunlight recorder
An instrument consisting essentially of a photoelectric cell filtered to respond to a specified wavelength region, an amplifier of sufficient gain to provide power enough to control movement of a...
superchromatic correction
Correction of an optical system at four separate wavelengths. This correction, longitudinal and lateral, is possible with the help of three selected special glasses.
superconductor
A metal, alloy or compound that loses its electrical resistance at temperatures below a certain transition temperature referred to as Tc. High-temperature superconductors occur near 130 K, while...
supercontinuum
Supercontinuum refers to a broad spectrum of light that spans a wide range of wavelengths, typically from the visible to the near-infrared or even mid-infrared regions of the electromagnetic...
superelastic collision
Observed phenomenon in laser pulses in which a large number of excited electrons are created and in which multiphoton processes have produced seed electrons, and excited neutral atoms are...
superfluorescence
The process in which the normal rate of fluorescent emission from a substance is enhanced by virtue of the optical gain of the medium; i.e., energy is lost not only by spontaneous emission but also...
superior mirage
An image of an object that appears above the object's true position as the result of abnormal refraction of the image rays by the atmosphere.
superliminal transmission
Superluminal transmission refers to the hypothetical process of transmitting information faster than the speed of light, which is commonly denoted as superluminal or faster-than-light (FTL)...
superluminescent light-emitting diode
An emitter based on stimulated emission with amplification but insufficient feedback for oscillation to build up.
superradiance
Directional and coherent radiation pulses that result from an ensemble of coherently prepared states in an optical medium.
superreflector
A reflector having a surface that has been superpolished to reduce residual sleeks and scratches and microroughness so that its scatter coefficient is low. Its surface is said to have a low-scatter...
superresolution
Superresolution refers to the enhancement or improvement of the spatial resolution beyond the conventional limits imposed by the diffraction of light. In the context of imaging, it is a set of...
supertwisted birefringent effect display
A liquid crystal display using the material in its supertwisted nematic phase; the birefringence of the liquid crystal results in a characteristic yellow or blue color, unless corrected.
supertwisted nematic phase
A form of liquid crystal in which the 90° twist of the twisted nematic phase has been increased to 180° or more, resulting in higher contrast and a wider viewer angle in the display.
supplementary lens
A meniscus that is often fitted before a camera lens to permit focusing on near objects.
suprathermal ion detector
A mass spectrometer used to detect ions formed by photo- and charge-exchange ionization of gases, such as those in the lunar atmosphere.
surface
1. In optics, one of the exterior faces of an optical element. 2. The process of grinding or generating the face of an optical element.
surface acoustic wave
An acoustic wave that propagates along the surface of a solid and decays exponentially with substrate depth. Also called a Rayleigh wave, it has both longitudinal and transverse (shear) components....
surface analysis by laser ionization
(SALI) A type of spectroscopy in which neutral atoms or molecules are ionized by an excimer laser beam and then measured by a time-of-flight mass spectrometer.
surface electromagnetic waves
Waves that propagate along the interface between two different media without radiation with exponentially decaying evanescent fields on both sides.
surface error
The departure of an optical surface from its required tolerance or figure.
surface normal -> normal
Sometimes referred to as the surface normal or 'surface norm'; the normal is an axis that forms right angles with a surface that light is incident upon or with other lines. The normal is used to...
surface plate
A large table with an accurately designed plane surface used to test other surfaces, or to provide a true surface for accurately locating a testing fixture. Most commonly made of granite.
surface profile
A representation of the shape of a surface, including any roughness or other irregularities. The profile can be generated by direct measurements, as by a stylus, or by remote measurement, as by an...
surface quality
The specification of allowable flaws in a surface by comparison to reference standards of quality. Two graded sets of surface quality standards are employed. The first denotes defects of a long...
surface quality standards
The standards of MIL-O-13830 set by the US government relative to tolerable surface scratches and other such defects in an optical system. A series of standard glass plates that have been...
surface reflection
Also known as Fresnel reflection. That portion of the incident radiation that is reflected from the surface of a refractive material. It is a function of the refractive index of the material. At...
surface wave
A wave that is guided by the interface between two different media or by a refractive index gradient in the medium. The field components of the wave may exist (in principle) throughout space, even to...
surface-emitting laser diode
A semiconductor laser diode that emits light perpendicular to the active region. The output radiation is taken through the surface as opposed to through a cleaved mirror.
surface-enhanced Raman optical data storage
A technique of optical storage whereby information is encoded by molecular alterations in the interaction between the optical layer and the substrate.

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