Progress in UCO's search for silver-based telescope mirror coatings

摘要

We report on the on-going effort at University of California Observatories Astronomical Coatings Lab to develop robustprotected-silver coatings suitable for telescope mirrors. We have identified a very promising recipe based on YFsub3/sub thatproduces excellent reflectivity at wavelengths of 340 nm and greater, has ~1.5% emissivity in the thermal IR, and doesnot contain problematic materials for the Mid-IR, such as SiOsub2/sub and Alsub2/subOsub3/sub. The recipe holds up extremely well toaggressive environmental testing (80C and 80% RH; high-Hsub2/subS atmosphere), and currently is being evaluated under realobservatory conditions. This coating may satisfy the need for telescope mirror coatings that are long-lasting (~5 years ormore) and have good reflectivity into the UV. We also evaluate and compare some other silver-based coatings developedelsewhere that should be useful in the same role.In addition, we describe recent upgrades to our coating facilities allowing us to deposit ion-assisted e-beam coatings onoptics up to ~1m. This novel arrangement places the e-gun and ion source on a pivoting "swing-arm", allowing theposition to move radially without changing the e-gun/ion source/ substrate geometry. Large substrates can be coated withgood uniformity using single-axis rotation only. This technique is scalable to arbitrarily large substrate sizes.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.