New approaches to the manufacture and metrology of light mirrors
As mentioned above, the very large telescopes of the future, such as E-ELT, will need
to have a primary mirror (42 m) made up of a great number of reflective segments, to be produced via a highly reproducible industrial process. A segmented mirror has even been proposed for the secondary mirror. INAF, in collaboration with ESO, is involved in the development of fabrication techniques and the associated ad hoc metrological procedures for these applications.
In particular, the studies in progress are concerned with:
- The development of light, hexagonal, SiC elements with an area of around 1 square metre for the primary mirror of the E-ELT. Such technology, alternative to the current baseline based on Zerodur, is particularly interesting because it is significantly lighter. Important industrial partners such as Galileo Avionica and Bettini spa are also participatingin this research.
- The development of thin, deformable mirrors (a few millimetres) made by hot casting in a reusable mould. This method is an alternative to the expensive and risky process of meniscus thinning of secondary mirrors used for example on the LBT. This work is carriedout in collaboration with ESO as part of the European OPTICON/FP6 project, and is producing very promising results.
- The use of the large "ion beam figuring" facility (2m x 3m) set up by INAF at OABr for extremely precise, non-contact correction of reflecting mirror segments (both primary and secondary) produced for the E-ELT.