PHOTOMULTIPLIER TUBES Basics and Applications THIRD EDITION PHOTON IS OUR BUSINESS ▲ Photomultiplier Tubes ▲ Photomultiplier Tube Modules Introduction Light detection technolgy is a powerful tool that provides deeper understanding of more sophisticated phenomena. Measurement using light offers unique advantages: for example, nondestructive analysis of a substance, high-speed properties and extremely high detectability. Recently, in particular, such advanced fields as scientific measurement, medical diagnosis and treatment, high energy physics, spectroscopy and biotech- nology require development of photodetectors that exhibit the ultimate in various performance parameters. Photodetectors or light sensors can be broadly divided by their operating principle into three major catego- ries: external photoelectric effect, internal photoelectric effect and thermal types. The external photoelectric effect is a phenomenon in which when light strikes a metal or semiconductor placed in a vacuum, electrons are emitted from its surface into the vacuum. Photomultiplier tubes (often abbreviated as PMT) make use of this external photoelectric effect and are superior in response speed and sensitivity (low-light-level detection). They are widely used in medical equipment, analytical instruments and industrial measurement systems. Light sensors utilizing the internal photoelectric effect are further divided into photoconductive types and photovoltaic types. Photoconductive cells represent the former, and PIN photodiodes the latter. Both types feature high sensitivity and miniature size, making them well suited for use as sensors in camera exposure meters, optical disk pickups and in optical communications. The thermal types, though their sensitivity is low, have no wavelength-dependence and are therefore used as temperature sensors in fire alarms, intrusion alarms, etc. This handbook has been structured as a technical handbook for photomultiplier tubes in order to provide the reader with comprehensive information on photomultiplier tubes. This handbook will help the user gain maximum performance from photomultiplier tubes and show how to properly operate them with higher reliability and stability. In particular, we believe that the first-time user will find this handbook beneficial as a guide to photomultiplier tubes. We also hope this handbook will be useful for engineers already experienced in photomultiplier tubes for upgrading performance characteristics. Information furnished by Hamamatsu Photonics is believed to be reliable. However, no responsibility is assumed for possible inaccuracies or omission. The contents of this manual are subject to change without notice. No patent rights are granted to any of the circuits described herein. ©2006 Hamamatsu Photonics K. K. CONTENTS CHAPTER 1 INTRODUCTION ............................................................ 1 1.1 Overview of This Manual ..................................................................... 2 1.2 Photometric Units ................................................................................ 4 1.2.1 Spectral regions and units ...................................................... 4 1.2.2 Units of light intensity ............................................................. 5 1.3 History ............................................................................................... 10 1.3.1 History of photocathodes...................................................... 10 1.3.2 History of photomultiplier tubes ............................................ 10 References in Chapter 1 ............................................................................... 12 CHAPTER 2 BASIC PRINCIPLES OF PHOTOMULTIPLIER TUBES ...................................... 13 2.1 Photoelectron Emission .................................................................... 14 2.2 Electron Trajectory ............................................................................ 16 2.3 Electron Multiplier (Dynode Section) ................................................. 17 2.4 Anode ................................................................................................ 18 References in Chapter 2 ............................................................................... 19 CHAPTER 3 BASIC OPERATING METHODS OF PHOTOMULTIPLIER TUBES ................................ 21 3.1 Using Photomultiplier Tubes ............................................................. 22 3.1.1 How to make the proper selection ........................................ 22 3.1.2 Peripheral devices ................................................................ 23 High-voltage power supply ......................................................................... 23 Voltage-divider circuit ................................................................................. 24 Housing ...................................................................................................... 26 Integral power supply module .................................................................... 27 3.1.3 Operating methods (connection circuits) .............................. 28 CHAPTER 4 CHARACTERISTICS OF PHOTOMULTIPLIER TUBES ...................................... 29 4.1 Basic Characteristics of Photocathodes ............................................ 30 4.1.1 Photocathode materials........................................................ 30 (1) Cs-I ...................................................................................................... 30 (2) Cs-Te ................................................................................................... 30 (3) Sb-Cs ................................................................................................... 30 (4) Bialkali (Sb-Rb-Cs, Sb-K-Cs) .............................................................. 30 (5) High temperature, low noise bialkali (Sb-Na-K) ................................... 31 (6) Multialkali (Sb-Na-K-Cs) ...................................................................... 31 (7) Ag-O-Cs ............................................................................................... 31 (8) GaAsP (Cs) .......................................................................................... 31 (9) GaAs (Cs) ............................................................................................ 31 (10) InGaAs (Cs) ......................................................................................... 31 (11) InP/InGaAsP(Cs), InP/InGaAs(Cs) ...................................................... 31 Transmission mode photocathodes ........................................................... 34 Reflection mode photocathodes ................................................................ 35 4.1.2 Window materials ................................................................. 36 (1) MgF2 crystal ......................................................................................... 36 (2) Sapphire .............................................................................................. 36 (3) Synthetic silica ..................................................................................... 36 (4) UV glass (UV-transmitting glass) ......................................................... 36 (5) Borosilicate glass ................................................................................. 36 4.1.3 Spectral response characteristics ........................................ 37 (1) Radiant sensitivity ................................................................................ 37 (2) Quantum efficiency .............................................................................. 37 (3) Measurement and calculation of spectral response characteristics .... 37 (4) Spectral response range (short and long wavelength limits) ..................... 38 4.1.4 Luminous sensitivity ............................................................. 38 (1) Cathode luminous sensitivity ............................................................... 39 (2) Anode luminous sensitivity .................................................................. 40 (3) Blue sensitivity index and red-to-white ratio ........................................ 41 4.1.5 Luminous sensitivity and spectral response ......................... 42 4.2 Basic Characteristics of Dynodes ..................................................... 43 4.2.1 Dynode types and features .................................................. 43 (1) Circular-cage type ............................................................................... 44 (2) Box-and-grid type ................................................................................ 44 (3) Linear-focused type ............................................................................. 44 (4) Venetian blind type .............................................................................. 44 (5) Mesh type ............................................................................................ 44 (6) MCP (Microchannel plate) ................................................................... 44 (7) Metal channel dynode ......................................................................... 44 (8) Electron bombardment type ................................................................ 44 4.2.2 Collection efficiency and gain (current amplification) ........... 45 (1) Collection efficiency ............................................................................. 45 (2) Gain (current amplification) ................................................................