Latest status of PMTs and related sensors

Abstract

Photomultiplier tubes (PMTs), which incorporate a photocathode and a dynode chain for electron multiplication in vacuum, are featured by high gain to detect a single photon and fast response time of nano second with large effective area up to 20 inches. Single-photon detection with such large effective area at low dark count rate of a few thousands Hz or less cannot be achieved by any other devices. Therefore, PMTs are still useful for various applications, such as biology, medical, chemistry, industry as well as high-energy physics experiments. Varieties of PMTs in effective area, photocathode material and electron multiplication mechanisms are available for individual purpose, furthermore, the PMTs are still evolving to satisfy the requirements from advanced frontier science, such as high-energy physics. One of the recent achievements is a big jump of photocathode sensitivity. Due to careful control of the photocathode process, the peak quantum efficiency of bialkali photocathode (ultra bialkali, UBA) reaches 43 %, for example for R7600, quite high compared to 27 % of conventional ones. Another challenge has been done on electron-multiplication stage to realize a hybrid photo-detector (HPD). Instead of the dynode chain, an avalanche diode is incorporated in a tube to receive and multiply electrons. A high-speed HPD has just been developed by adjusting transit time of electrons from the photocathode and the avalanche diode, as well as using a small avalanche diode for fast time response. This HPD shows a single-photon timing resolution of 50 ps in FWHM and a high gain of 105. In this article, recent advancements of PMTs and related sensors will be described. © Copyright owned by the author(s).