Optimization of Protected Silver Coating Recipes for E-ELT Telescope Mirrors (Conference Presentation)

Most telescope mirrors of the European ELT shall have protected silver coatings that are highly reflective across all astronomic wavelength bands from the UV (370 nm) to the far infrared. Another aspect is that the coatings shall be frequently cleaned in situ, so they must be highly durable against abrasion and chemical agents such as sulfur and salt. However, they also must be easy to strip with a non-toxic etchant before each recoating. We identify trades and optimize silver coating recipes with different protection layer materials and thicknesses to meet these partly contradictory objectives. A test coating campaign is ongoing.