Introduction to Photomultiplier Tubes Michael Mastanduno Kelly Michaelsen
Outline History Review Photoelectric Effect and Secondary Emission PMT Overview PMT Parts Breakdown-Photocathode, Dynode, Anode PMT Timing, Linearity, Uniformity Materials of PMT Dark Current Quantum Efficiency Single Photon Counting Applications
History 1902 Secondary Emission 1905: Photoelectric Effect 1934: First photomultiplier Ongoing improvements by RCA corporation Today, Japan based Hamamatsu Photonics is a leader www.mnhs.org
Photoelectric Effect http://www.physics.hku.hk/~phys0607/images/photoelectric.jpg
Secondary Emission Metallic Surface Incoming Electron Outgoing Electrons
Photomultiplier Tubes Window-Interface with the World Photocathode-Easily Ionized Metal Dynodes-Different Voltage Potentials Anode-Photocurrent Produced http://www.olympusmicro.com/primer/flash/ photomultiplier/index.html http://www.frankswebspace.org.uk/physics/physicsgce/images/pmt.gif
Photocathode Thin deposit on the entry window of the PMT Electrons made due to the photoelectric effect Focusing electrode focuses the electrons toward the dynodes Electrons leave with the energy of the incoming photons minus the work function of the photocathode http://sales.hamamatsu.com/en
Dynode Each dynode is held at a higher positive voltage than the previous one Electrons accelerate between dynodes Emit more electrons with each dynode thanks to secondary emission coating http://quarknet.fnal.gov/projects/pmt/student/images/pmtpic.gif http://www.sge.com/uploads/-g/fc/-gfcpk9wvqktowymj60n3a/elec_mult_work_fig_3.gif
Anode Site of charge accumulation Current pulse emitted Peak Current = Gain*e/FWHM for single e www.beckerhickl.de/pdf/a mpmt.pdf
Timing PMTson the whole have fast time response Rise Time-from 10 to 90% increase in peak height Fall Time-from 10 to 90% decrease in peak height Transit Time-Photocathode to Anode Fast PMT-Spherical inner window http://sales.hamamatsu.com/en
Linearity For each incident photon, signal is the same If too much light, linearity affected by anode If too little light, linearity affected by dynode C. Carpenter
Uniformity Variation in output sensitivity depending on the position (of photocathode or anode) Uniformity decreases at longer wavelength http://sales.hamamatsu.com/en
Photomultiplier Tube Types Head On or End On Design Side On Design http://upload.wikimedia.org/wikiped ia/commons/3/36/pmside.jpg http://sales.hamamatsu.com/assets/img /products/etd/det/pmt/photo/r7639_p.jpg
Window Types Determines the short wavelength limit for the PMT http://sales.hamamatsu.com/en http://www.electronicsurplus.com/objects/catalog/product/image/img76405.jpg
Photocathode Types Semiconductor of Alkali metal with low work function About 10 used depending on the desired function Reflection (Opaque) or Transmission (Semitransparent) Types http://www.stanfordcomputeroptic s.com/image/mcpsinglephotocathode.jpg
Spectral Response http://sales.hamamatsu.com/en
Dynode Types http://sales.hamamatsu.com/en
Dark Current Small current always running Caused by: Radiation Components base current Max QE just below radiant sensitivity http://sales.hamamatsu.com/en
Quantum Efficiency Usually expressed in % Highest for photons just below peak sensitivity
Photon Counting Mode Gain set high enough (100 db) to get current from 1 photon Lower quantum efficiency means not all photons counted Raman spectroscopy and fluorescence analysis http://sales.hamamatsu.com/en
Stability in Single Photon Mode http://sales.hamamatsu.com/en
Applications Electric Eyes Nuclear and particle radiation detectors Measuring intensity and spectrum of light emitting materials Nuclear medicine, microscopy Chemical analysis http://sales.hamamatsu.com/en
Hamamatsu R6357 PMT Side on detection λ= 185 to 900 nm Peak sensitivity 450nm UV Glass window Multialkali Photocathode http://sales.hamamatsu.com/en
Light Detection Large dynamic range Tuneablegain settings applied to the dynode chain http://sales.hamamatsu.com/en
PMT Calibration C. Carpenter
PMT Noise C. Carpenter
Amplitude vs. Phase
PMT Noise Amplitude output voltages 100 mv to 1 V Phase output voltage good 8 mv to 1V Repeatability suffers for lower light levels (<100mV) C. Carpenter
Outline History Review Photoelectric Effect and Secondary Emission PMT Overview PMT Parts Breakdown-Photocathode, Dynode, Anode PMT Timing, Linearity, Uniformity Materials of PMT Dark Current Quantum Efficiency Single Photon Counting Applications