Optical devices to increase photocathode quantum efficiency

Maximum quantum efficiencies attainable with commercially available semitransparent photocathodes are near 30% (for blue light). Work in the Instrumentation Division at Ames Research Center, NASA, has achieved quantum efficiencies as high as 58% with these same photocathodes through the use of optical enhancement. Improvement ratios in the red and near ir are even larger, but of course, the original sensitivities are smaller at these wavelengths. In addition to simply improving sensitivity, effort is also directed toward extending the applicability of the technique. A new class of devices recently conceived at Ames Research Center will allow application of optical enhancement to TV camera tubes, image intensifiers, and other imaging detectors. This paper describes the optical enhancement work in detail with major emphasis on results in the areas mentioned above.