The Photomultiplier Handbook

Abstract

This handbook is aimed at helping users of PMTs who are faced with the challenge of designing sensitive light detectors for scientific and industrial purposes. The raison d’être for photomultipliers (PMTs) stems from four intrinsic attributes: large detection area, high, and noiseless gain, and wide bandwidth. Detection involves a conversion process from photons to photoelectrons at the photocathode. Photoelectrons are subsequently collected and increased in number by the action of an incorporated electron multiplier. Photon detection, charge multiplication, and many PMT applications are statistical in nature. For this reason appropriate statistical treatments are provided and derived from first principles. PMTs are characterized by a range of photocathodes offering detection over UV to infra-red wavelengths, the sensitivities of which can be calibrated by National Laboratories. The optical interface between light sources and PMTs, particularly for diffuse or uncollimated light, is sparsely covered in the scientific literature. The theory of light guides, Winston cones, and other light concentrators points to means for optimizing light collection subject to the constraints of Liouville’s theorem (étandue). Certain PMTs can detect single photons but are restricted by the limitations of unwanted background ranging in magnitude from a fraction of a photoelectron equivalent to hundreds of photoelectrons. These sources, together with their correlated nature, are examined in detail. Photomultiplier biasing requires a voltage divider comprising a series of resistors or active components, such as FETs. Correct biasing provides the key to linear operation and so considerable attention is given to the treatment of this topic. Electronic circuits and modules that perform the functions of charge to voltage conversion, pulse shaping, and impedance matching are analysed in detail.