Reflectivity, polarization properties, and durability of metallic mirror coatings for the European Solar Telescope

摘要

In the context of the conceptual design study for the European Solar Telescope (EST) we have investigateddifferent metallic mirror coatings in terms of reflectivity, polarization properties and durability. Samples of thefollowing coating types have been studied: bare aluminum, silver with different dielectric layers for protectionand UV enhancement, and an aluminum-silver combination. From 2009 to 2011 we have carried out a long-termdurability test under realistic observing conditions at the VTT solar telescope of the Observatorio delTeide (Tenerife, Spain), accompanied by repeated reflectivity measurements in the EST spectral working range(0.3 - 20 μm), and by polarization measurements in the visible range. The test results allow us to find theoptimum coatings for the different mirrors in the EST beampath and to eventually assess aging effects andre-coating cycles. The results of the polarization measurements are a valuable input for an EST telescopepolarization model, helping to meet the stringent requirements on polarimetric accuracy.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.