Durable coatings for large segmented mirrors

Abstract

The reflective coatings applied to telescope mirrors affect not only the optical performance, but also affect significantly the telescope operation. Replacement of a primary segment of a large segmented mirror is expected to be a major event. An increased service life span of such segment is of enormous value. The optics community is currently aggressively pursuing development in broadband high reflective durable coatings. We are undertaking research with the goal of a high, broadband reflective coatings that, with appropriate cleaning and in situ maintenance, will provide a service life time of more than seven years. Based on the VLOT (Very Large Optical Telescope) project requirements, we conducted a literature search on available materials, thin film deposition and cleaning processes to get as much information as possible. The results of this survey will be presented as the starting point of our study. Different thin film processes have been identified but energetic processes such as Reactive Low Voltage Ion Plating (RLVIP), Magnetron Sputtering and Ion Beam Assisted Deposition (IBAD) will be of great interest for durable coating fabrication. Regarding the cleaning process, we have concentrated our effort on laser cleaning processes.