ZWe report on the efficient operation of a CsI-coated GEM photon detector.
We describe its operation mode and the dependence of the single electron de
tection efficiency on the electric fields. Conditions for obtaining full ef
ficiency of photoelectron extraction and their focusing into the GEM apertu
res, in 1 atmCH(4), are presented. The quantum efficiency of the CsI-coated
GEM is 35% at 150 nm. (C) 2001 Elsevier Science B.V. All rights reserved.