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Extremely durable glass-ceramic From Wikipedia, the free encyclopedia
Zerodur is a lithium-aluminosilicate glass-ceramic manufactured by Schott AG. Zerodur has a near zero coefficient of thermal expansion (CTE), and is used for high-precision applications in telescope optics, microlithography machines and inertial navigation systems.
The main applications for Zerodur include telescope optics in astronomy[2] and space applications,[3] lithography machines for microchips and displays,[4] and inertial measurements systems for navigation.[5][6]
In astronomy, it is used for mirror substrates in large telescopes such as the Hobby-Eberly Telescope,[7] the Keck I and Keck II telescopes,[8] the Gran Telescopio Canarias,[9] the Devasthal Optical Telescope,[10] the European Southern Observatory's 8.2 m Very Large Telescope,[11] and the 39 m Extremely Large Telescope.[12]
In space, it has been used for the primary mirror of SOFIA’s telescope,[13] for the imager in Meteosat Earth observation satellites,[14] and for the optical bench in the LISA Pathfinder mission.[15]
In microlithography, Zerodur is used in wafer steppers and scanner machines for precise and reproducible wafer positioning.[16][17] It is also used as a component in refractive optics for photolithography.[18]
In inertial measurement units, Zerodur is used in ring laser gyroscopes.[19]
Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties[20] are:
Schott, under Jürgen Petzoldt, began developing glass-ceramics in the 1960s, in response to demand for low expansion glass ceramics for telescopes.[25]
In 1966, Hans Elsässer, the founding director of the Max Planck Institute for Astronomy, asked the company if it could produce large castings of almost 4 meters using low-expansion glass-ceramic for telescope mirror substrates. The order for a 3.6 m (12 ft) mirror blank, along with ten smaller mirror substrates was accepted in November 1968. Development ended by December 1969, and the mirrors were delivered by late 1975.[25]
In 1984, the mirror substrate went into operation in a telescope at the Calar Alto Observatory in Spain. Further orders for mirror blanks subsequently followed.[26]
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