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] It also has been used for the primary mirror of SOFIA's airborne telescope. [13]
ASA also produces some telescopes with zerodur. [14]
In space, it has been used for the imager in Meteosat Earth observation satellites, [15] and for the optical bench in the LISA Pathfinder mission. [16]
In microlithography, Zerodur is used in wafer steppers and scanner machines for precise and reproducible wafer positioning. [17] [18] It is also used as a component in refractive optics for photolithography. [19]
In inertial measurement units, Zerodur is used in ring laser gyroscopes. [20]
Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties [21] are:
Schott began developing glass-ceramics in the 1960s lead by Jürgen Petzoldt, in response to demand for low expansion glass ceramics for telescopes. [26]
In 1966, Hans Elsässer, the founding director of the Max Planck Institute for Astronomy (MPIA), asked the company if it could produce large castings of almost 4 meters using low-expansion glass-ceramic for telescope mirror substrates. In 1969, the MPIA ordered a 3.6 m (12 ft) mirror blank, along with ten smaller mirror substrates. The mirrors were delivered by late 1975, [26] and went into operation in 1984 in a telescope at the Calar Alto Observatory in Spain. Further orders for mirror blanks followed. [27]