All kinds of local faults in material, typically of a circular crosssection, including stringy knots, small stones, sand and crystals. They are marked in accordance with ISO 10110 standard requirements.

The invisible portion of the electromagnetic spectrum that lies between approximately from 780 nm to 1 mm. For better classification, this type of radiation is subdivided into: Near Infrared, Middle Infrared and Far Infrared.

describes the amount of variance in the refractive index within the volume of an optical component. It is defined as the difference between the maximum and the minimum value of a component’s refractive index.

A phenomenon which is typical of transversal waves (direction of oscillation and direction of propagation are mutually orthogonal). Transversal waves include electromagnetic waves and, hence, also light. Two or more superimposing waves of identical wavelength and identical polarization state will add to or compensate each other.

Instrument that employs the interference of light waves to measure the accuracy of optical surfaces. Essentially, the various types of interferometers rely on the same principle: two or more beams of light are routed through separate optical paths (via mirrors and/or semi-transparent plates) to be recombined at the end. Depending on the amount of difference in optical path length, an interferential pattern will show. This pattern can be rings or stripes.

Refer to “Infrared Radiation”

describes the amount of variance of spherical surfaces against an ideal ball shape.