Quantum efficiencies of imaging detectors with alkali halide photocathodes. 1: Microchannel plates with separate and integral Csl photocathodes.
We have measured and compared the quantum efficiencies of microchannel plate (MCP) detectors in the far- UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiencies were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are ~15% at 1216 A for a CsI-coated MCP compared with 65% for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20% for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.
Carruthers
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