Polishing the first VLT main mirror (1995)

The first of the four VLT Zerodur blanks was ready at the Schott Glaswerke in July 1993. From here they were transported by ship to the REOSC workshop in Saint Pierre du Perray near Paris. This new facility, unique in the world, was specifically conceived, built and equipped to polish and test the large VLT mirrors. It is equipped with two machines: one for grinding, the other for polishing, and both with a 150 actuator system in order to support the thin and flexible, 23.5 tons mirrors.

Here the blank underwent a difficult two-year polishing process, at the limits of present technology. Thanks in particular to an efficient, built-in `learning' process, the new, computerised polishing system progressively optimized the procedures. The optical surfaces of the following blanks were brought into the desired form in significantly less time.

This is an unusual view of the first VLT primary mirror taken from the top of the impressive test tower at the REOSC facility during optical tests in 1995.