Microchannel plate intensifier gain uniformity improvement in sealed tubes by selective scrubbing

摘要

We have improved the gain uniformity of sealed microchannel plate image intensifiers (MCPIs) by selectively scrubbing the high gain sections with a controlled bright light source. The major contributor to poor uniformity on most of the tubes we have tested is the cathode, with the MCP and screen making only minor contributions. Using the premise that ions returning to the cathode from the MCP damage the cathode and reduce its sensitivity, we raster scanned an HeNe laser beam light source across the cathode of an MCPI tube. Cathode current was monitored and when it exceeded a present threshold, the sweep rate was decreased 1000 times, giving 1000 times the exposure to cathode areas with sensitivity greater than the threshold. The threshold was set at the cathode current corresponding to the lowest sensitivity in the active cathode area so that sensitivity of the entire cathode would be reduced to this level. This process reduced tube gain by between 10% and 30% in the high gain areas while gain reduction in low gain areas was negligible. Effects on cathode spectral sensitivity and phosphor efficiency, the results of including the MCP in the feedback loop, the possibility of reclaiming tubes damaged by prolonged exposure to resolution targets, and circuit details are discussed.