An UHV box coater for VUV reflective coatings on mirror substrates of up to 95 cm in diameter

Large mirrors with excellent reflectivity in the vacuum ultraviolet (VUV) range down to 140 nm are needed for large area RICH detectors with CsI photocathodes. This demand can only be fulfilled with a thin homogenous aluminium layer on a substrate with very low surface roughness. Due to the base metal properties of Al an excellent vacuum is required during the evaporation-condensation process. In addition the Al film needs suitable protective layers on both surfaces. tup of pilot plants to investigate deposition parameters are described and the design of an appropriate box coater is presented.