Materials
The optical properties of the lining of the sphere greatly affect its accuracy. Different coatings must be used at visible, infrared and ultraviolet wavelengths. High-powered illumination sources may heat or damage the coating, so an integrating sphere will be rated for a maximum level of incident power. Various coating materials are used. Early experimenters used a deposit of magnesium oxide. Barium sulfate has a usefully flat reflectance over the visible spectrum. Finely-deposited gold is used for infrared measurements. Various proprietary PTFE compounds are also used for visible light measurements.
The theory of the integrating sphere assumes a uniform inside surface. Openings where light can exit or enter, normally called ports, that are used for detectors and sources must be small, less than about 5% of the surface area of the sphere, for the theoretical assumptions to be valid. Unused ports should therefor have matching plugs, with the interior surface of the plug coated with the same material as the rest of the sphere. Baffles are normally inserted in the sphere to block the direct path of light from a source to a detector, since this light will have non-uniform distribution.
Read more about this topic: Integrating Sphere
Famous quotes containing the word materials:
“In how few words, for instance, the Greeks would have told the story of Abelard and Heloise, making but a sentence of our classical dictionary.... We moderns, on the other hand, collect only the raw materials of biography and history, “memoirs to serve for a history,” which is but materials to serve for a mythology.”
—Henry David Thoreau (1817–1862)
“In daily life what distinguishes the master is the using those materials he has, instead of looking about for what are more renowned, or what others have used well.”
—Ralph Waldo Emerson (1803–1882)
“Young children learn in a different manner from that of older children and adults, yet we can teach them many things if we adapt our materials and mode of instruction to their level of ability. But we miseducate young children when we assume that their learning abilities are comparable to those of older children and that they can be taught with materials and with the same instructional procedures appropriate to school-age children.”
—David Elkind (20th century)