Soft x-ray and extreme ultraviolet quantum detection efficiency of potassium chloride photocathode layers on...

We present measurements of the quantum detectio efficiency (QDE) of potassium chloride, applied directly to the surface of a microchannel plate (MCP), over the 44-1460-A wavelength range. The contributions of the photocathode material in the channels, and on the interchannel web, to the QDE have been determined. Two broad peaks in the QDE centered at lambda congruent with 500 A and lambda congruent with 900 A are apparent, the former with ~40% peak QDE and the latter with ~30% peak QDE. The photoelectric threshold is observed at lambda ~1400 A, and there is a narrow QDE minimum at lambda~ 670 A, which correlates with 2xthe band gap energy for KC1. The angular variation of the QDE from 0 to 35 degrees to the channel axis has also been examined. We describe a simple QDE model and show that its predictions are in accord with our QDE measurements. Assessment of the stability of KC1 shows that there was no significant degradation of the QDE at wavelengths of