Definitions of Common Terms<!--Definitions obtained from The Photonics Dictionary Definitions of Optical Terms-->


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Definitions of Common Terms:

Types of
Glass

BK7
A borosilicate crown optical glass with high homogeneity, low bubble and inclusion content. Its good physical and chemical properties make it widely used in visible and near IR range. Most of windows, lenses and prisms, which used in laser, optical system, optical communication, are made from BK7 glass.

Fused Quartz
Crystal quartz that is melted at a white heat and cooled to form an amorphous glass. It is not birefringent and the refractive index is much lower than that of crystal quartz. Fused quartz of optical quality can be prepared by suitable techniques.

Fused Silica
Glass consisting of almost pure silicon dioxide (SiO2). Also called vitreous silica. Frequently used in optical fibers and windows.

Optical Glass
A glass that, during manufacture, is carefully controlled with respect to composition, melting, heat treatment, and other processing, to render it's optical characteristics, such as it's index of refraction,dispersion, transmittance, spectral transmittance, homogeneity, freedom from birefringence, permanence,etc.,sufficient for it's optical application

Pyrex
Trade name for a type of borosilicate glass manufactured by Corning Glass Works, noted for its low coefficient of thermal expansion. Used most often for mirror blanks; not suitable for light transmission.

ULE®
Exclusive to Corning, ULE zero expansion glass .

Zerodur®
Schott Glass Technologies' trade name for a glass-ceramic material with a very low coefficient of thermal expansion.

Additional Information

Interferogram
A photographic or electronic recording of an optical interference pattern.
Interferometry
The study and utilization of interference phenomena, based on the wave properties of light.
Interferometer
An instrument that employs the interference of lightwaves to measure the accuracy of optical surfaces; it can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light. Interferometers are used extensively for testing optical elements during manufacture. Typical designs include the Michelson, Twyman-Green and Fizeau interferometers.
Optics
That branch of physical science concerned with vision and certain phenomena of electromagnetic radiation in the wavelength range extending from the vacuum ultraviolet at about 40 nm to the far-infrared at 1 mm. Now being replaced by the more inclusive term photonics.
Optical Figure
The amount by which an optical surface deviates from its ideal design value, expressed in wavelengths of light.
Optical Flat
A piece of glass, pyrex or quartz having one or both surfaces carefully ground and polished plano, generally flat to less than a tenth of a wavelength.
Optical Testing
Refers to a variety of methods and tools used to determine the surface contour and performance of optical components and systems.

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