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The large telescopes nowadays under development will have the adaptive optics systems fully integrated from the
beginning of the project. These optics are in fact an essential component that is necessary for the full exploitation of the
performances obtainable from the large optics foreseen in these instruments. Due to the large reflecting areas of these
telescopes their adaptive optics systems will use probably thin segmented mirrors, assembled to create a single surface,
placed along the optical train. Today, a number of telescopes (MMT, LBT, etc) have the monolithic secondary mirror of
the instrument used as a component of the adaptive optic system. The technique used for the production of these single
pieces thin mirror shells, typically having convex shape, is not well suited for the manufacturing of the large number of
segments necessaries for the future telescopes. Infact, the procedure foresees the thinning of conventional thick mirrors, a
technique expensive and time consuming. It is hence necessary to find a better approach able to produce thin optical
segments in a cost effective way and with short delivery time. In this study, financed in the frame of OPTICON-FP6, the
Astronomical Observatory of Brera (INAF-OAB) is investigating a technique for the manufacturing of these optical
components that has the potential to fulfill these requirements. The curved optical segments that are under development
will have a thickness of few mm and will be made in BorofloatTM glass. The technique foresees the thermal slumping of
thin glass segments using a high quality ceramic mold as a master to impart a precise shape to the glass. The initially flat
glass segment is placed onto the mold and then, by means of a suitable thermal cycle, the material is softened so to copy
the master shape. If necessary, at the end of the slumping is foreseen the correction of the eventual remaining errors using
the Ion Beam Figuring technique. This paper describes the process of production of the optical segments and the status of
the investigation.
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