Definitions

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.

A meniscus that is often fitted before a camera lens to permit focusing on near objects.

A mass spectrometer used to detect ions formed by photo- and charge-exchange ionization of gases, such as those in the lunar atmosphere.

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.

(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.

Waves that propagate along the interface between two different media without radiation with exponentially decaying evanescent fields on both sides.

The departure of an optical surface from its required tolerance or figure.

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.

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...

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...

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...

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...

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...

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.

A technique of optical storage whereby information is encoded by molecular alterations in the interaction between the optical layer and the substrate.

Surface-enhanced Raman scattering (SERS) is a powerful analytical technique that enhances the Raman scattering signal of molecules adsorbed on or near certain nanostructured surfaces. Raman...

Surface-enhanced Raman spectroscopy (SERS) is an analytical technique that combines the principles of Raman spectroscopy with the enhancement provided by nanostructured metallic surfaces. Raman...

A surface-mount device (SMD) is an electronic component that is mounted directly onto the surface of a printed circuit board (PCB) rather than being inserted into holes drilled in the board (as with...

A term that describes both the color and intensity of the immediate environment of the object or image being viewed.

Instruments used for measuring angles and occasionally lengths on the ground. The principal surveying instruments are the level, the stadia telescope, the transit and the theodolite. Laser...

A small telescope mounted on a tripod and free to rotate about a vertical axis. A spirit level is mounted over the telescope and adjusted so that when the bubble is central, the telescope axis is...

In a laser, the voltage necessary to sustain a constant operating current, somewhat less than that needed for start-up.

The material removed during diamond machining of glass components.

Swept-source optical coherence tomography is an imaging technique used in medical diagnostics, particularly in ophthalmology, to visualize and analyze the internal structures of biological tissues,...

A swept-source laser, also known as a wavelength-swept laser, is a type of laser that rapidly and continuously changes its emission wavelength over time. This continuous wavelength tuning is achieved...

A positive after-image that is maintained for a minute or more.

The length of the oscillation of a grinding or polishing lap.

A lens system made up of two sets of similar lenses, each of which compensates for many of the aberrations produced by the other. The lens sets are arranged symmetrically on either side of the...

Any systemic process that ultimately reassembles all the system's components into their initial alignment, or an arrangement that exactly reproduces the initial relative alignment.

A synapse is a specialized junction between two neurons (nerve cells) or between a neuron and a target cell (such as a muscle or gland cell). It is the fundamental functional unit of communication in...

Abbreviation of "synchronization.'' In television, the timing signals used to drive the scanning process. Horizontal sync triggers the retracing of the raster line beginning at the left-hand...

A detector sensitive only to signals close to or at a particular frequency that is the same as the frequency of a control signal applied independently. The synchronous detector also is...

A standard for fiber optic telecommunications interfaces, with a 1300-nm data link operating over single-mode fiber at data rates of 52, 155 and 622 Mb/s.

The technique of generating ultrashort -- down to subpicosecond -- pulses by pumping a dye laser with mode-locked laser pumps with cavity lengths the same as, or a submultiple of, that of the dye...

A mode of transmission whereby the sending and receiving stations operate continuously at a fixed relationship of phase and frequency, generating signals to control the timing of the data that are to...

A synchrotron is a type of particle accelerator that uses magnetic fields to steer charged particles, typically electrons or positrons, in a closed, circular or elliptical path. The name synchrotron...

Radiation emitted by electrons when they travel in circular orbits at speeds close to that of light. Synchrotron radiation occurs in the x-ray and ultraviolet regions of the spectrum. Once considered...

Imaging radar that increases the sweep of its along-track (or azimuth) capacity by measuring not only the time delay of the echoes returning from the microwave pulse transmitted by its antenna (or...

An imaging technique in which an object moving through an interference field formed in space scatters light and is spatially recorded on a photographic film as a hologram. If the interference field...

A combination of components arranged so as to perform at least one function.

Abbreviated SoC. A single chip containing all the electronic circuits required for a complete, working product. SoCs are similar to microcontroller technology but provide additional components. A SoC...

The equivalent f number of a fictitious lens that has a circular opening and 100 percent transmittance, which would give the same central illumination as the lens being considered: where...

See honeycomb table; indexing table.

An instrument designed to measure the rate of rotation of components, such as shafts.

One lumen-second, the SI unit of the quantity of light.

The series of interference bands that appear in the spectrum when a specified glass plate is inserted into a spectroscope, from the side of the blue portion of the spectrum, so that the plate...

The law stating that the brightness of an object that is examined through a slotted disc, rotating over a critical frequency, is proportional to the angular aperture divided by the opaque sectors.

In optics, a shape often given to the leading edge of a projectile. In any side view it appears as a pointed arc, while any cross section perpendicular to its long axis appears as a circle.