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PhotodetectorsPhotodetectors
Philippe Mangeot CEA/DSM/DAPNIA
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IntroductionIntroductionScope of the tutorialScope of the tutorial
Light detection of photons from UV to IRLight Pulses measurementsImagingBasics in physics principles, technology and applications
Out of scope Out of scope (my choice !)(my choice !)Film or phosphor image plateSolar photovoltaic silicon cellsDirect X ray or far UV detection and imagingBolometer or far IR detectionExotic and/or lab devices (quantum dots or wells, heterostructure, multibandgap…)
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SourcesSourcesMost important sources were borrowed from the web pages of :
• Hamamatsu : http://sales.hamamatsu.com/en/home.php• Photonis : http://www.photonis.com/• Electron Tubes Limited : http://www.electrontubes.com/• e2v Technologies : http://e2vtechnologies.com/ (formerly EEV)• Delft Electronics Products: http://www.dep.nl/•SensL : http://www.sensl.com/•Micron : http://www.micron.com/•and many others
from the web pages of Amos Breskinhttp://www.weizmann.ac.il/home/detlab/
And from many other lectures and presentations, in particular by:Katsushi Arisaka (UCLA)Thomas Patzak (IN2P3 / APC)Jerry Blazey (Northern Illinois University)
Thank you and many apologizes (overall for the ones I forgot to cite!)
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Applications of Applications of photodetectorsphotodetectorsEverywhere !Everywhere !
Look around you, they are everywhere, you donLook around you, they are everywhere, you don’’t even know or notice !t even know or notice !Media (digital camera, camcorder, cell phones, CD reader…)Telecom (optical fiber links, optical couplers…)Laser applications (measurement, gas analysis, barcode readers…)Medicine (gamma and PET camera, digital X rays, endoscopies…)Biology ( DNA sequencing, Immuno-assay, biochip…)Industry (chemical and surface analysis, process control, shape analysis…)Defense (night vision, earth observation…)Mining (oil well logging, rock analysis…)Physics (a rather small part of the market !)
• Solid state, synchrotron radiation, plasma science• Particle and nuclear physics • astronomy and astrophysics
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Types of Types of photodetectorsphotodetectors
Vacuum devicesVacuum devicesPhotomultiplierMultichannel platesHybrid photon detectors
Solid state devicesSolid state devicesPhotodiodes, phototransistors and PIN diodesAvalanche photodiodesSilicon photo multipliersImaging arrays photo sensor
• Charge coupled devices• CMOS Active Pixel Sensor• a:SiH Thin Film Transistor array
Gaseous Gaseous photodetectorsphotodetectorsDrift and MWPC
• Gas photocathode• Solid photocathode
Micropattern gas chamber
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Some photometric unitsSome photometric unitsCandela
•• Luminous intensityLuminous intensity of a source E=1,464.10-3 watt/stéradian @ 555nm • Amount of light produced by 1/60 cm² of a black body @ 2046 K
Lumen•• luminous fluxluminous flux through a solid angle of 1 steradian by a source of 1Cd
Lux• unit of illuminationillumination : 1 lumen per square meter
Direct sunlight 100,000 - 130,000 lux
Full daylight, indirect sunlight 10,000 - 20,000 lux
Overcast day 1,000 lux
Indoor office 200 - 400 lux
Very dark day 100 lux
Twilight 10 lux
Deep twilight 1 lux
Full moon 0.1 lux
Quarter moon 0.01 lux
Moonless clear night sky 0.001 lux
Moonless overcast night sky 0.0001 lux
1 Watt = 683 lumen @ 555 nm1 Watt = 683 lumen @ 555 nm
Photo detector sensitivityOften given in A/lm
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Vacuum Devices : PMTVacuum Devices : PMT
PrinciplePrinciple
photon
photoelectronSecondaryelectrons
photocathode
Glass window
dynodesecondary emission δi ≅ 2 - 10
anode Lastdynode
SocketHV dividerpreamp
Glass tubeVacuum = 10-4 P
focusingelectrode
Gain : G = δ1⋅δ2⋅δ3 ⋅⋅⋅ δnCharge : E=Nγ⋅QE⋅CE⋅G
QE =Quantum efficiencyCE= collection efficiency
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Vacuum Devices : PMTVacuum Devices : PMT
Main parameters and performancesMain parameters and performancesQuantum Efficiency (QE) 20 to 30% @ 400 nmPhotoelectron Collection Efficiency (CE) 70 to 90%Gain (G) up to 107
Excess Noise Factor (ENF) ~ 1.3 (see later)
Energy Resolution (σ/E)
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Vacuum Devices : PMTVacuum Devices : PMT
Photocathode Quantum Efficiency (QE)Comparison to emission spectra of common Comparison to emission spectra of common scintillatorscintillator materialsmaterials
Bialkali:• Sb-Rb-Cs• Sb-K-Cs
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Vacuum Devices : PMTVacuum Devices : PMTPhotocathode Quantum Efficiency (QE)
Various photocathode materialsVarious photocathode materials
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Vacuum Devices : PMTVacuum Devices : PMT
Transmittance of glass windows
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Vacuum Devices : PMTVacuum Devices : PMT
Secondary emission
Gain
δ = a . Vk
a : constant k = 0.7 to 0.8
G = CE. δ1. δ2. δ2. …δi….. δn
where δi = secondary émission coeff of ith dynode
nknknnk VAnVaEaG ⋅⋅ ⋅=+
⋅=⋅= )1
()(
Assuming uniform voltage drop between dynodes
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Vacuum Devices : PMTVacuum Devices : PMT
Gain and dark current
ThermalPhotoelectronEmission
LeakageCurrent
FieldEffect
This and the 2 next slides from a lecture of Katsushi Katsushi ArisakaArisaka (UCLA)
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Vacuum Devices : PMTVacuum Devices : PMT
Energy resolution, Excess Noise Factor• Ideal case
• Real case : electronic noise (ENC) and amplification statistics (ENF)
• Excess Noise Factor
2
2
Input
OutputENFσσ
≡
γγ
γσNN
NE
1==
2
⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅⋅⋅+
⋅⋅=
PGCEQENENC
CEQENENF
E γγ
σ
Increase of the variance of energy distribution due to amplification statistics
n
ENFδδδδδδ ⋅⋅⋅⋅
+⋅⋅⋅+⋅
++=21211
1111For a PMT with n dynodes
The first dynode secondary emission The first dynode secondary emission coeffcoeff dominatesdominates
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Vacuum Devices : PMTVacuum Devices : PMT
Single photon detection
ENF is related to Peak to Valley RatioIf δ1 >>5 => ENF<1.4
Clear single PE can be seen.
111121211_
−=⋅⋅⋅⋅
+⋅⋅⋅+⋅
+=⎟⎠⎞
⎜⎝⎛ ENFE nPESingle δδδδδδσ
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Vacuum Devices : PMTVacuum Devices : PMT
Dynode geometryDynode geometry
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Vacuum Devices : PMTVacuum Devices : PMTTiming propertiesTiming properties
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Vacuum Devices : PMTVacuum Devices : PMT
Basic peamplifier scheme
Voltage divider bias circuit
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Vacuum Devices : PMTVacuum Devices : PMT
They come in many different shapes, size (up to 20” !) and performances.One of the most important market is medical imaging 300000 PMT’s year.(2000 gammas camera/year, 80 PMT’s200 PET cameras 800 PMT’s)
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Vacuum Devices : PMTVacuum Devices : PMT
Applications and marketApplications and marketMedical imagingIndustry (oil and mining)Physics
Excerpt from HAMAMATSU applications guide from their web site
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Vacuum Devices : MCPVacuum Devices : MCP
Multi Channel PlateMulti Channel PlateStructure and principle
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Vacuum Devices : MCPVacuum Devices : MCP
Structure and principlephoton photoelectronphotocathode
∆V ~ 300 V
∆V ~ 3000 V
∆V ~ 300 V
Glass window
dual MCPGain ~ 106
Anode may be pixilated
Chevron structure :•reduces space charge•reduces ion feedback•Increases gain
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Vacuum Devices : MCPVacuum Devices : MCPTechnology
• Monofiber draw• Multifiber stack and draw• Billet stacking• Slicing (θ~ 5 to 10°)• Etching of core glass• Reduction of lead glass
– H2 @ 250 to 450°C– =>Semiconductive layer
• Vacuum deposition– NiCr electrodes
Core : hard etchable glassCladding : lead glass
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Vacuum Devices : MCPVacuum Devices : MCP
Main parameters and performancesMain parameters and performancesGain
• single stage : G ~ 103 to 104
• Dual MCP : G ~ 106 to 107
• Low transient time ~1 ns• Transient time spread ~100 ps• Sub-ns rise and fall time
Function of :α = Ratio Length/diameterδ =secondary emission coeffG =exp ( K . G =exp ( K . αα))
K = f(HV, α) gain factor
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Vacuum Devices : MCPVacuum Devices : MCP
Applications• Light or image intensifier, night and IR vision
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Vacuum Devices : MCPVacuum Devices : MCP
Applicationsimage intensifier
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Vacuum Devices : HPDVacuum Devices : HPD
Hybrid Photon DetectorHybrid Photon DetectorBasic
• Photon conversion • Electrostatic acceleration
– 10 to 30 kV
• Ionization in Si detector– 3.6 eV for e-h pair– PD : Q ≤ HV / 3.6– APD additional gain ~ 50
• Imaging capability– Electrostatic optics or
proximity focussing– Pixelized detector– R/O ASIC aboard
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Vacuum Devices : HPDVacuum Devices : HPD
Hybrid Photon DetectorHybrid Photon DetectorTechnology
5” HPDBialkali KCsSb UV extendSi 2048 ch 1x1mm²HV = 20 kVC.Joram Beaune 2002
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Vacuum Devices : HPDVacuum Devices : HPD
Main parameters and performances
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Vacuum DevicesVacuum Devices
Other devices : multi stage phototubesOther devices : multi stage phototubes
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Typical Values and Resolution Typical Values and Resolution of Various Photon Detectors of Various Photon Detectors
QEQE CColol δδii ENFENF GG ENCENC σσ/E/E
IdealIdeal 1.01.0 1.01.0 10001000
1010
--
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10001000
10001000
1.01.0 101066 00 √√1/N1/N
PMTPMT 0.30.3 0.90.9 1.31.3 101066 101033 √√4/N4/N
PDPD 0.80.8 1.01.0 1.01.0 11 101033 √√1.4/N+(1000/N)1.4/N+(1000/N)22
APDAPD 0.80.8 1.01.0 2.02.0 100100 101033 √√3/N+(14/N)3/N+(14/N)22
HPDHPD 0.30.3 0.950.95 1.01.0 101033 101033 √√3/N+(3/N)3/N+(3/N)22
HAPDHAPD 0.30.3 0.950.95 1.01.0 101055 101033 √√3/N3/N
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⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅⋅⋅+
⋅⋅=
PGCEQENENC
CEQENENF
E γγ
σ
From a lecture of Katsushi Katsushi ArisakaArisaka (UCLA)
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Solid state Solid state photodetectorsphotodetectors : PD: PD
Photodiodes, phototransistorPhotodiodes, phototransistorBasic
• Bulk Si =>N layer• P layer on top (boron doped)• Depleted zone between P and N• If Eλ > Eg (1.12 eV for Si)→e- jump to conduction band→h+ left in valence band→e- (h+) drift to N (P) layer→current
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Solid state Solid state photodetectorsphotodetectors : PD: PD
Reverse bias• Photo conductive mode (instead of photovoltaic)• Increase depletion zone thickness• Reduce junction capacitance • Increase speed
Phototransistor• Very commonly used device
PIN diode• Add an intrinsic layer• Between P N layers• Same results as reverse bias
– + reduction dark noise– Increase speed– Higher absorption coeff
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Solid state Solid state photodetectorsphotodetectors : PD: PD
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Solid state : APDSolid state : APD
Avalanche Avalanche PhotoDiodePhotoDiodeBasic
• Photons create e- h+ pairs in intrinsic zone
• Electrons drift to depleted zone• Multiplication by ionizing
collisions
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Solid state : APDSolid state : APD
Active Area 5x5 mm2
Operating Voltage @ M=50 ~380 V
Capacitance @ M=50 80 pF
Serial Resistance 3 Ω
Dark Current @ M=50 < 10 nA
Excess Noise Factor @ M=50 ~2
Quantum Efficiency @ 470 nm 80 %
dM/dV x 1/M @ M=50 3.0 %/V
dM/dT x 1/M @ M=50 -2.4 %/K
Summary of APD parameters
Applications Applications Main application : optical link Physics :
• CMS e-cal
APD`s designed for the CMS ECALBy Hamamatsu Photonics
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Solid state : APDSolid state : APD
CMS eCMS e--cal cal APDAPD’’ss
0.1
1
10
100
1000
10000
0 50 100 150 200 250 300 350 400 450
Voltage [V]
Gai
n
0
10
20
30
40
50
60
70
80
90
100
300 400 500 600 700 800 900 1000Wavelength [nm]
Qua
ntum
Effi
cien
cy [%
]
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Solid state : Solid state : SiPMSiPM
Silicon Photomultiplier Silicon Photomultiplier Small depleted layer (0.5 µm) very high field =>Geiger avalancheSimilar : MRS (Metal-Resistor-Semiconductor)
array of small Geiger APDs onto the same substrate (less then 1 photon per cell)Geiger discharge quenched by passive resistor (400kΩ) on each pixel
P. Buzhan et alMEPhI & PULSAR in Moskow
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Solid state : Solid state : SiPMSiPM
Main properties
SiPM pulse height distributionLED illumination
Gain versus bias voltageG = Cpix.(Vbias – Vbreak)/eslope gives pixel capacity (C = 41fF)
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Solid state : Solid state : SiPMSiPM
Some problems
Quantum efficiency :• Low for a Si device• low fill factor• thickness of front layer
Dark noise vs bias voltageDecrease to 10 kHz at -50°C @ G= 106
P. Buzhan et al. NIM A 504 (2003) 48-52
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Solid state : VLPCSolid state : VLPC
Visible Light Photon Visible Light Photon CounterCounter
Formerly “Solid State Photo Multiplier” by RockwellPrinciple of Operation
• Impact ionization of As doped impurities in Si (En ~ 54meV)
• Impurity band conduction (conduction hopping at low temp.)
• Single carrier photomultiplication
•+ •-
IntrinsicRegion
GainRegion
DriftRegion
SpacerRegion
Photon
•h
Substrate
•e
D+ flow
E field
Undoped Silicon
(Blocking) Layer
Doped Silicon Layer
Heavy As doping
Gain Region
Drift Region
Top Contact (+)
Bottom Contact (-)
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Solid state : VLPCSolid state : VLPC
Scifi tracker of DØ8 pixels VLPC chip
Advantages• Quantum Efficiency ~ 90%• Avalanche gain ~ 30,000• Pulse duration ~ 1nsec
Disadvantages• High dark counts ~ 20,000/s• Highly sensitive to room temp.
IR photons•• 6 to 9 K operation temp6 to 9 K operation temp
Low light level LED calibration
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Solid state Arrays: CCDSolid state Arrays: CCD
Charge Coupled DeviceCharge Coupled DevicePrinciple
• Array of small Photodiodes• Light integration• Transfer thru the matrix
Transfer from well to well (pixel)2 phases clocked gates Detail of a pixel and
operation principle
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Solid state Arrays: CCDSolid state Arrays: CCD
Readout architectureReadout architecture
interline transferFast frame transfer
Full frame transferSmearing : needs a shutter but simpler chip
Frame transferLong exposures
Typical R/O speed = 5 MHz⇒FFT at 5 frames /s for a1024x1024 pixel CCD
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Solid state Arrays: CCDSolid state Arrays: CCD
Main parametersMain parametersQuantum efficiency
• Front illumination : QE ~ 50% range λ = 400 to 800 nm• Back illumination : QE 80% range λ = 200 to 1000 nm
Dark signal at 293 K ~ 1000 to 10000 e-/pixel/s
Quantum efficiency of CCDBack vs front illumination
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Solid state Arrays: CCDSolid state Arrays: CCD
ApplicationsApplicationsConsumer media equipment Scientific : spectrometry, biomedical imaging…Astronomy
The focal plane of MEGACAMTelescope CFH (Hawaii)• 40 CCD’s• e2v Technologies model CCD42-90• 2048x4612 pixels (13.5 x 13.5 µm²)• Back illuminated (λ 350 to 1000 nm)• Cooling at - 120°C• 400 Mpixel, 30s readout • 80 Go of data / night
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Solid state Arrays: APSSolid state Arrays: APS
Active Pixel Sensor : CMOS imager Active Pixel Sensor : CMOS imager Matrix of pixels = photodiodes + preamp and gatesrandom addressing R/O Classical CMOS processing
PhotodiodeActive-Pixel Architecture
PhotogateActive-Pixel Architecture
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Solid state Arrays: APSSolid state Arrays: APS
Main parameters and Main parameters and performancesperformances
Sensitivity : 1 to 2 V/lux-secDark noise : 10 mV/s @ 60°CDynamic : 40 to 60dB (depends from ADC on chip)Speed : up to 200 frames/s in VGA format (640x480 pix)Size : up to ½” 4000 x 4000 pix (3 x 3 µm²)Low cost, standard IC processing, high yieldBut :Low efficiency : poor fill factor (microlenses improve)
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Solid state Arrays: APSSolid state Arrays: APS
ApplicationsApplicationsCamera “on chip”Low cost still camera, web cam, process and shape control
Quality and performances steadily improveQuality and performances steadily improveMedical applications : dental X ray , endoscopy
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Solid state Arrays: above ICSolid state Arrays: above IC
Above IC : Smart Pixel and TFAAbove IC : Smart Pixel and TFASeparate photon conversion and R/O electronicSeparate photon conversion and R/O electronic
“smart pixel”• Photodiode array bonded on top of R/O chip
Thin Film on ASIC• a-Si:H evaporated on top of R/O ASIC
Other development at CERNPierre Jaron
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Solid state Arrays: TFTSolid state Arrays: TFT
Imaging plate : aImaging plate : a--Si:HSi:HThin Film TransistorThin Film Transistor
Same design and process than LCD flat screens
• Matrix of amorphous Silicon transistors evaporated on top of glass panel , plastic film or Siwafer
• H and V random addressing readout
May be coupled to scintillator
• Gd2O2S:Tb phosphor screens or CsI(TI) scintillating layers
• Digital X ray plate => columnar grown polycrystalline CsI
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Solid state Arrays: TFTSolid state Arrays: TFT
Main performancesMain performancesSize : up to 400 x 400 mm², 3000 x 3000 pixelsFill factor : 30 to 70%Readout time : up to 30 frame/sDynamic : 14 bit
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Gaseous photo detectorsGaseous photo detectors
Gaseous photocathodeGaseous photocathodeTEA, TMAEMultistage chamberdrift chamber (DELPHI,SLD)
Solid photocathodeSolid photocathodeCsI and other stuffWire or pad chamber, asymmetric drift chamberMicro pattern gas chamber
• Micromegas• GEM• Gaseous phototubes
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Gaseous photo detectorsGaseous photo detectors
E.Nappi INFN Bari Beaune 2002
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Gaseous photo detectorsGaseous photo detectors
Gaseous photocathodeGaseous photocathodeTEA, TMAE
• Photon conversion directly on gas molecule• Eλ must be > Ionization potential of gas • Most gas have Eion > 10 eV => λ = 1240/10 = 124 nm far UV• But
– TEA triethylamine [(C2H5)3N] EEionion=7.5 eV=7.5 eV– TMAE tetrakis(dimethylamino)ethylene. [C10H24N4 ] EEionion=6.1eV=6.1eV
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Gaseous photo detectorsGaseous photo detectors
Multistage chamber• First RICH in operation• E605 at FNAL• 15 m He radiator• 2 chambers• 40 x 80 cm²• Ar +TEA• 3% TEA (bubbling @ 10°C)• Gain 4.106 to 107
Advantages of TEA• High vapor pressure• Good QE• Small free mean path for UV
disadvantages of TEA• Too high threshold 7.5 eV (165 nm)• Need UV optic (mirror,windows)• Needs very high transmission Cerenkov medium
MgF window
Conversion gapPreamp gap
Drift gap
MWPC0 V-2000 V
-3000 V-6000 V-6500 V
-2000 V
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Gaseous photo detectorsGaseous photo detectors
drift chamber (DELPHI,SLD, OMEGA)• TMAE
– Use of quartz windows– High QE
• Thick detector– Improve absorption
• Drift zone– Eliminate parallaxe
• End detector– X , Z detection– Time => Z coordinate
• Drawback of TMAE– Low vapor pressure– Long absorption range– Could need to warm up– Aggressive stuff
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Gaseous photo detectorsGaseous photo detectors
Solid photocathodeSolid photocathodeCsI first choice
• Quartz windows• Good QE• Gas resistant
– If no H2O or polluants
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Gaseous photo detectorsGaseous photo detectors
Micro pattern gas detectorMicro pattern gas detectorMicromegas
3 mm
100 µm
-800 V
-500 V
0 V
Drift space
Amplification space
Photon transmissionPhoton reflection
CsI photocathode may be deposited under the drift electrode (transmission mode) or on top of the micromesh (reflection)High gain reachable:•Low ion/photon feedback•Optical screening
Single photon amplitude spectrum CsI photo cathodeY.GiomatarisNucl.Instrum.Meth.A449:314-321,2000
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Gaseous photo detectorsGaseous photo detectors
Micro pattern gas detectorMicro pattern gas detectorGEM
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Gaseous photomultiplierGaseous photomultiplierPossible extension of QE to visible lightBialkali photocathode in sealed detectorUltra pure CH4 or Ar/CH4
Multi GEM provides• High gain• No ion/photon feedback• Good single PE detection
Very exciting perspectiveVery exciting perspective
Amos Amos BreskinBreskin et al et al WeizmannWeizmann Institute of ScienceInstitute of Science
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TheThe EndEnd
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Vacuum Devices : MCPVacuum Devices : MCP
MCP pores microphotography