LETTER TO THE EDITOR: Quantum efficiency measurements of an uncoated CEM in the range 0.14 - 160 nm (9 keV - 8 eV)

The quantum efficiency of an uncoated channel electron multiplier (CEM) working in the photon-counting regime has been evaluated over a wide spectral range, which comprises the EUV and soft x-ray regions. Three different experimental set-ups have been used: a Johnson - Onaka monochromator for the 30 - 160 nm region, a grazing incidence monochromator for the 0.3 - 30 nm region and a test facility mounting filters for the 0.14 - 0.3 nm region. As a secondary standard, both silicon and aluminium photodiodes have been used. The efficiency has been evaluated at normal incidence angle. The measured values range from 2% to 15% in the range 0.14 - 100 nm, while a rapid decrease is present over 120 nm. Changes in the efficiency due to carbon contamination in the vacuum system are discussed, and also effects due to variations of the illuminated area on the CEM entrance cone.