Download Introduction to Photomultiplier Tubes

Introduction to Photomultiplier
Tubes
Michael Mastanduno
Kelly Michaelsen
Outline
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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
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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
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PMTs on 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
http://upload.wikimedia.org/wikiped
ia/commons/3/36/Pmside.jpg
Side On Design
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
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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
• Tuneable gain
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