First light secondary mirror for LBT

Thales Seso was awarded the contract for the optical polishing and control of the “first light” secondary mirror of the LBT (Φ980mm) The unit was produced and delivered to the LBT project though a contract placed by the Ohio State University.

In order to get at the earliest a “first light” of the Large Binocular Telescope (LBT-Arizona) even if the deformable secondary mirror (2 units for 2 channels) were not ready at the same time of primary ones (also 2 units), the LBT project decided to install on one channel a provisional solid state mirror, optically representative of the reflective surface made with adaptive optics, of course besides operational efficiency.

The main characteristics and specifications of this mirror are:

• Size : circular Φ 980mm
• Shape: elliptic Concave with about 200µm asphericity from best fit sphere
• Substrate: Borosilicate lightened structure made with “Hextek” process
• Optical quality required (valid for fist light mirror only):
o WFE < 250nm for full CA
o WFE < 50nm RMS for sub-apertures Φ 50mm
• Coating: protected aluminium