On the efficient electron transfer through GEM

The absolute electron transfer efficiency of a gas electron multiplier (GEM) was systematically measured in several gas types and pressures and over a broad range of electric-field configurations, using a single-electron pulse-counting method. A complete understanding of the role played by the relevant variables was obtained; particularly, the critical part of electron transport in the gap preceding the GEM was demonstrated. A small electron multiplication in this gap was shown to result in a full detection efficiency of single-electron events, under proper gas diffusion and multiplication conditions. The relevance to single electron and single photon detection is discussed. The experimental results are in good agreement with simulation calculations.