The largest optical telescope in the world – the European Extremely Large Telescope, or E-ELT for short – is currently being built on the Chilean mountain Cerro Armazones.

The giant telescope is based on a five-mirror design: a giant main mirror (M1) and four smaller mirrors (M2 to M5) as reflectors.

Schott has been awarded a contract for the production of mirror substrates for the secondary (M2) and tertiary mirrors (M3) of the European Extremely Large Telescope.

Schott was awarded the latest contract to supply mirror substrates following the successful use of Zerodur glass-ceramic in the M4 mirror last year.

The special feature of Zerodur glass-ceramic as a mirror substrate is its extremely low thermal expansion coefficient.

This means that even in the case of large temperature fluctuations, the material does not expand.

Even chemically, the material is very resistant and can be polished very well.

The actual mirror layer with its extremely smooth surface made of aluminium or silver is usually deposited with vapour shortly before the telescope is put into operation.

The result is extremely sharp images for exploring unrivaled worlds.

“We are very pleased to be part of the groundbreaking E-ELT project.

“In order to continue to satisfy the sustained high demand for Zerodur glass-ceramic in the areas of IC/LCD lithography, aviation and metrology, we will be putting a second melting tank into operation at the main plant in Mainz shortly,” said Andreas Haedrich, Vice President of Sales for the Optical Industry at Schott.

“In total, we’ve invested a double-digit million figure in ZERODUR production in order to secure and further expand our excellent market position for the future.”

In the E-ELT project of the European Southern Observatory (ESO), these features are especially effective because the design is ambitious: the 39.3 metre primary mirror, also called ‘Mirror 1’ or ‘M1,’ collects light from the night sky and reflects it on a smaller mirror, the M2, which is four metres in diameter.

This in turn reflects the light to a reflector (M3) placed in the centre of the M1.

The task of this third mirror is to irradiate the light onto an adaptive optics (M4) placed above it, which changes its surface a thousand times a second and thus straightens the distorted starlight again.