High reflectivity large scale telescope mirror coatings via long throw sputtering

Here we present reflectivity measurements of long throw sputtered aluminum coatings at normal and oblique incidence angles on glass test chips. Experimental results indicate that water vapor partial pressure, not incident angle, is the dominant factor for front surface reflectivity of sputtered aluminum. These results highlight the importance of water vapor pumping in telescope mirror coating vacuum chambers and indicate that long-throw sputtering is an economical and reliable technique for producing high uniformity, high reflectivity mirror coatings across large substrates.