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]
Infrared astronomy is a sub-discipline of astronomy which specializes in the observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers, and falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.
The Overwhelmingly Large Telescope (OWL) was a conceptual design by the European Southern Observatory (ESO) organization for an extremely large telescope, which was intended to have a single aperture of 100 meters in diameter. Because of the complexity and cost of building a telescope of this unprecedented size, ESO has decided to focus on the 39-meter diameter Extremely Large Telescope instead.
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have 10 m (33 ft) aperture primary mirrors, and, when completed in 1993 and 1996, they were the largest optical reflecting telescopes in the world. They are currently the third and fourth largest.
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, and mechanical stress. Without active optics, the construction of 8 metre class telescopes is not possible, nor would telescopes with segmented mirrors be feasible.
The Gran Telescopio Canarias is a 10.4 m (410 in) reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands, Spain. It is the world's largest single-aperture optical telescope.
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The Stratospheric Observatory For Infrared Astronomy (SOFIA) was a 80/20 joint project of NASA and the German Aerospace Center (DLR) to construct and maintain an airborne observatory. NASA awarded the contract for the development of the aircraft, operation of the observatory and management of the American part of the project to the Universities Space Research Association (USRA) in 1996. The DSI managed the German parts of the project which were primarily science-and telescope-related. SOFIA's telescope saw first light on May 26, 2010. SOFIA was the successor to the Kuiper Airborne Observatory. During 10-hour, overnight flights, it observed celestial magnetic fields, star-forming regions, comets, nebulae, and the Galactic Center.
The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984.
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Schott AG is a German multinational glass company specializing in the manufacture of glass and glass-ceramics. Headquartered in Mainz, Rhineland-Palatinate, Germany, it is owned by the Carl Zeiss Foundation. The company's founder and namesake, Otto Schott, is credited with the invention of borosilicate glass.
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An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, nebulas and galaxies by means of interferometry. The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation, called baseline, between the component telescopes. The main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.
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Sitall is a crystalline glass-ceramic with ultra-low coefficient of thermal expansion (CTE). It was originally manufactured in the former Soviet Union and was used in the making of primary mirrors for the Russian Maksutov telescopes, but since dissolution has diminished in quality. It has a CTE of only 0 ± 1.5×10−7 °C−1 in the temperature range −60 to 60 °C, placing it in a small group of transparent materials with low CTE such as Vycor, Zerodur, Cer‑Vit and fused quartz.
Cer-vit is a family of glass-ceramic materials that were invented by Owens Illinois in the mid-1960s. Its principle ingredients are the oxides of lithium, aluminum and silicon. It is melted to form a glass which is then heat treated to nucleate and crystallize it into a material that is more than 90% microscopic crystals. Its formulation and heat treatment can be modified to produce a variety of material properties. One form is a material that is transparent and has a near zero thermal expansion. Its transparency is because the microscopic crystals are smaller than the wave length of light and are transparent, and its low thermal expansion is because they have a spodumene structure.
Yerkes 41-inch reflector is a 40-inch aperture (101.6 cm) reflecting telescope at the Yerkes Observatory, that was completed in 1968. It is known as the 41 inch to avoid confusion with a 40 inch refractor at the observatory. Optically it is a Ritchey–Chrétien design, and the main mirror uses low expansion glass. The telescope was used as a testbed for an adaptive optics system in the 1990s.