Production of 300 paraboloidal mirrors with high reflectivity for use in the Barrel RICH counter in DELPHI at LEP

Abstract

Mirrors have been produced industrially by heat-forming 6 mm thick float-glass at about 610°C, followed by vacuum deposition of a 50 nm thick layer of Al and a 60 nm thick protective layer of MgF 2, using a fabrication method first developed at CERN. The successful implementation of this method for industrial production, and the quality control of the mirrors, are described. An average reflectivity of more than 85% in the wavelength region 165–200 nm has been achieved in the production. The focal spot obtained by shining parallel light on the mirrors contained, on the average, 98% of the light within a circle of 1.2 mm diameter.