eso9818 — Organisation Release

VLT 8.2-m Mirror Ready for Coating

19 May 1998

With the VLT UT1 First Light just one week away, the ultimate activities that lead up to this important event have started at the Paranal Observatory. Following successful optical alignment tests, cf. ESO Press Release 05/98 , the 8.2-m primary mirror has been removed from the first Unit Telescope (UT1). It is now in the Mirror Maintenance Building (MMB) and is being prepared for coating with a thin, highly reflective aluminium layer.

The giant coating plant has been thoroughly checked and test runs have shown that it is ready to receive the 22-tonnes Zerodur mirror. Several firings were performed during the past days that deposited a proper layer of aluminium on a test target. The specialists have now decided to do the real thing tomorrow, Wednesday, May 20.

The procedure involves moving the big mirror from its cell unto the supports of the lower half of the vacuum vessel (coating tank). The mirror surface will be thoroughly cleaned to remove any dust and other impurities. The lower half of the tank will then be attached to the upper part in which the source of aluminium is placed. The process is based on high-rate magnetron sputtering under high vacuum (< 2. 10 -4 Pa). It is carried out while the mirror rotates in order to obtain a uniform and highly reflective layer of aluminium on the polished mirror surface.

Following this operation, the mirror will again be placed in its cell and returned to the telescope. After careful optical re-alignment, expedited by the newly gained experience, the Test Camera will be activated. The first astronomical images will be obtained, marking the moment of First Light .

The following electronic images illustrate the recent work.

More information about the Very Large Telescope (VLT) project is available on the ESO Web.

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