Realization of a high vacuum evaporation system for wave-length shifter deposition on photo-detector windows

In this paper, the authors present a system based on a vacuum chamber and Knudsen cells that can evaporate organic materials on convex surfaces up to 10 in. diameter, with a good uniformity, in a very short time. This system was successfully used at CERN for the deposition of tetra-phenyl butadiene wavelength shifter on the 8 in. window of 360 Hamamatsu R5912-MOD photomultiplier tubes (PMTs), before their installation inside the ICARUS T600 detector to be used for neutrino physics studies. The quantum efficiency in the vacuum ultraviolet region measured on the whole photocathode shows a good uniformity over the entire PMT active surface with an average value above 10% from 120 to 200 nm.