Status and perspectives of vacuum-based photon detectors for single photon detection

Recent developments in vacuum-based photon detectors for single photon detection, in particular, innovative techniques such as position-sensitive hybrid photon detectors and photo-multiplier tubes, have stimulated increased interest from a variety of fields. These devices are sensitive to single photons with an energy spectrum defined by the transmission of the optical entrance window and the photo-cathode type. Their spatial resolution ranges from a few millimetres, for pad hybrid photon detectors and multi-anode photo-multiplier tubes, down to a few tens of microns for pixel hybrid photon detectors. Basic technological and design aspects are assessed in this paper. The performance of such devices in terms of gain, intrinsic speed, single- and multiple photon counting capability, active-to-total area ratio, and magnetic field sensitivity are discussed. Specific problems related to the particular front-end and readout electronics requirements are outlined. Examples of applications are given, and some current research and development programmes are presented.