AGC selected to deliver third coater for the large mirrors of the world’s largest telescope

The European Southern Observatory (ESO) and AGC Glass Europe, with its business unit AGC Plasma Technology Solutions, have signed a second contract to deliver a coater specially equipped for the large mirrors (M2, M3, M4 and M5) of the world’s largest telescope⁽¹⁾. 

The ESO telescope will be installed in the Atacama desert (Chilean Andes) at Cerro Armazones (3,046 m) equipped with a gigantic 39-meter segmented primary mirror and additional 4-meter wide large mirrors. The telescope has the purpose to acquire scientific data to study the universe and through specific observations address certain unsolved problems of fundamental physics, study exoplanets and investigate other objects and phenomena across the universe.

In 2018 AGC was already selected to assemble and install the two magnetron sputtering coaters⁽²⁾ for the primary mirror segments of the Extremely Large Telescope (ELT). The third coater is for the additional 4-meter wide mirrors. The magnetron sputtering coaters are important to maintain the performance of the telescope optics. It is necessary to have the coaters on site for ESO to be able to re-coat the mirror segments regularly with a protected silver layer stack. The telescope’s location in the Chilean desert knows harsh climate conditions, such as sandstorms, that affect the silver layers of the mirrors, therefore regular recoating is required. The newly ordered coater will be installed in the dedicated section of the telescope’s technical facility on the Paranal observatory site in Chile within 32 months. 

Patrick Van Bortel, VP Industrial & New Businesses of AGC Glass Europe comments: “It is a great honour to be selected again by the European Southern Observatory for this ELT Large Coating Plant. The coating plant for the segments of the primary mirror, which is also supplied by the team of AGC Plasma Technology Solutions, has arrived in Chile and is ready for on-site assembly. The coating plant that is now ordered by ESO will be used for coating the 4-meter wide convex secondary mirror and concave tertiary mirror, as well as the fourth and fifth mirror. That implicates that all large area mirrors of the ELT will be manufactured with coating equipment supplied by AGC”.

The uniformity control of the highly reflective coating over the entire surface of the 4-meter wide mirrors is a real challenge for this project. AGC is proposing a technical solution by including an Online Shimmable Magnet Bar technology⁽³⁾ in the cathodes that allows superior thickness control of the deposited thin layers. The teams of AGC Plasma Technology Solutions in Gosselies, Belgium and in Lauenförde, Germany are acknowledged for their expertise and know-how in building custom-designed plasma coating equipment.

(1) More info on the world’s largest telescope on https://elt.eso.org/ 
(2) See the presentation about the coating plant for M1, presented at the SPIE conference, on YouTube  
(3) Online Shimmable Magnet Bar Technology (iOSMB): The working principle of iOSMB technology is a magnet bar which consists of a series of individual magnets known as yokes. Each individual yoke can be positioned in height relative to the target surface with motors controlled by integrated electronics. The independent control of each individual yoke enables locally precise control of the magnetic field strength along the entire cathode length. This allows users unprecedented control of coating thickness uniformity on large area substrates and curved objects.