Single photoelectron detection with a low-pressure gas electron multiplier coupled to a CsI photocathode

We have operated the Gas Electron Multiplier (GEM) coupled to a CsI photocathode for the detection of single UV photons. Gains of up to 10 000 were observed with a single GEM in pure hydrocarbons in the range 40–400 Torr. Using a double-GEM structure, we have detected single photoelectrons on a strip electrode. We have studied the single-electron detection efficiency of the GEM, a crucial parameter in its operation in single-photon detection applications, both experimentally and by simulation.