VUV reflective coatings on thin concave float glass substrates with a perimeter of 86 cm to be used as provisional HADES RICH mirror segments

The setup in the UHV box coater for the HADES RICH mirrors was modified to deposit VUV reflective layers on large area substrates. These substrates were made of 2 mm thick float glass with 87 cm spherical curvature and a perimeter of 86 cm. A good uniformity of the coatings could be obtained by a larger source-to-substrate distance of 155 cm. Impurity problems due to lower deposition rates had to be avoided with a better process vacuum. The modified setup, the thickness calibrations, uniformity tests, process conditions and reflectivity measurements are presented.