HIGH-EFFICIENCY PHOTOCATHODES FOR GASEOUS DETECTORS OF VISIBLE PHOTONS

Our latest results in the development of gaseous detectors for visible photons are presented in this paper. Quantum efficiencies of a few pe rcent at 400 nm were routinely achieved. These detectors can operate a t gas gains up to similar to 1000, The main effort was focused on a st udy of the effect of different liquids and solid layers on the quantum efficiency of photocathodes. Some of these layers make the photocatho des more robust, while others increase the quantum efficiency. It was found, for example, that thin layers of solid and liquid Xe and Kr enh ance the quantum efficiency by a factor similar to 2. These solid laye rs can also protect the photocathodes against some impurities in the s urrounding gas. After some further development gaseous detectors for v isible photons will probably find applications in crystal calorimetry, noble liquid scintillation detectors, Cherenkov counters, air shower detectors and the readout of scintillating fibers for preshower and ma x-shower detectors.