Abstract
We have measured the quantum efficiency (QE) of CsI photocathodes as a function of the electric field strength in a parallel-plate geometry, in CH 4, C 2H 6 and i-C 4H 10 both in charge collection and multiplication modes. It was found that in the collection plateau the QE value in gases is lower compared to that of vacuum and is independent of the field; in gas media the QE starts to increase at the transition between collection and multiplication modes and reaches the vacuum value at high gas gain. We explain this effect by a decrease of the electron-molecule elastic backscattering while entering the multiplication mode. We conclude that the electric field effects observed here, would also apply for other photocathodes and gas mixtures. An enhancement of the QE after microdischarges was observed and is discussed in detail.
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