Extraneous Light Emission from Photomultipliers

This paper describes various extraneous light-emission phenomena that limit the application of the photomultiplier, or photomultipliers in coincidence, to the detection of light levels higher than that limit set by thermionic emission from the photocathode or photocathodes. The paper discusses four sources of extraneous light within the photomultiplier: (1) electrode glow; (2) dielectric glow, which includes electro-luminescence and phosphorescence; (3) Cerenkov radiation and faceplate scintillations; and (4) residual gases within the volume of the photomultiplier. Data are given on the timing, the pulse-height distribution, and the efficiency of various light-emission processes. A brief summary is given on the recent progress made toward the reduction of extrinsic noise activity encountered in photomultipliers operated at light levels in the order of a few quanta per second.