Improving the UV reflectance of the aluminum coating of the 4m SOAR Telescope in the Gemini 8-m sputtering coating facility

The SOAR telescope was designed to have a bare Aluminum coating. This coating is performed in the Gemini-South sputtering facility. Two coatings have been done on the SOAR mirror (2004 and 2009). On both occasions, the reflectivity obtained for the UV-blue were lower than the reflectivity of the nominal bare Aluminum. Various tests have been done during 2018 and 2019, in order to reach a higher reflectivity in the UV, including changes in the coating recipe. We report here the progress to date, the performance that we have reached and the problems we have faced in this 8-meter coating facility.

[1]  Maxime Boccas,et al.  Coating the 8-m Gemini telescopes with protected silver , 2004, SPIE Astronomical Telescopes + Instrumentation.

[2]  Maxime Boccas,et al.  Gemini's protected silver coatings: first two years in operation , 2006, SPIE Astronomical Telescopes + Instrumentation.

[3]  Maxime Boccas,et al.  Protected-silver coatings for the 8-m Gemini telescope mirrors , 2006 .

[4]  Raymond N. Wilson,et al.  Reflecting Telescope Optics II , 1999 .