Further investigation of CsI-coated microchannel plate quantum efficiencies

Previously we have reported pulse-counting detection efficiencies measured for CsI-coated microchannel plate (MCP) detectors (two-stage chevron configuration with a single collecting anode) to be 15-20% near Lyman-alpha (1216 A), compared to typical 65% quantum yields of opaque CsI photocathodes. To investigate the possibility that an improvement in quantum yield could result from use of MCPs with a bias angle of ~25 degrees , instead of 8 degrees as used previously, we repeated our measurements with new MCPs having the larger bias angle. No significant improvement in detection efficiency was achieved; the new detector tests still yielded maximum efficiencies of the order of 20% near 1216 A.