Infrared Secondary Has a New Silver Coat

May 16, 2003

Silver recoating of the infrared secondary mirror was completed successfully in the beginning of April. The work was done in Hawaii, using Subaru's mirror coating facility within the telescope enclosure on Mauna Kea. Unlike the primary mirror which is coated with aluminum, the infrared secondary mirror was coated with silver which is more refective than aluminum in the infrared. After recoating, the secondary mirror had a surface reflectivity of 99%, the highest attainable at infrared wavelengths. The mirror has been back in normal operation since April 11.

Infrared Secondary Mirror after recoating. The reflectivity of a reference glass coated at the same time. Assembling the infrared secondary mirror.

The primary mirror collects light from astronomical objects and reflects it towards prime focus at the top of the telescope. At prime focus, the light either enters an observing instrument (Suprime-Cam), or is reflected by a secondary mirror towards an instrument at another focus. The infrared secondary mirror is used for instruments such as IRCS, CIAO, COMICS and OHS. It is 1.3 meters in diameter and weighs 185-kilograms. Subaru also has two optical secondary mirrors for use with FOCAS and HDS.


Exchanging the secondary mirror with an instrument.



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