highest qe‘s measured so far razmick mirzoyan, max-planck-institute for physics munich, germany
TRANSCRIPT
Highest QE‘s Measured So Far
Razmick Mirzoyan,
Max-Planck-Institute for PhysicsMax-Planck-Institute for Physics
Munich, GermanyMunich, Germany
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Quantum Efficiency
Quantum efficiency (QE) of a sensor is defined Quantum efficiency (QE) of a sensor is defined as the ratioas the ratio
QE = N(ph.e.) : N(photons)QE = N(ph.e.) : N(photons) Conversion of a photon into ph.e. is a purely Conversion of a photon into ph.e. is a purely
binomial process (and not poisson !)binomial process (and not poisson !) Assume Assume NN photons photons are impinging onto a are impinging onto a
photocathode and every photon has the photocathode and every photon has the same same probability probability PP to kick out a ph.e.. to kick out a ph.e..
Then the Then the meanmean number of ph.e.s is number of ph.e.s is N x PN x P and the and the VarianceVariance is equal to is equal to N x P x (1 – P)N x P x (1 – P)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Differences between binomial and poisson distributions
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Signal to noise ratio
The signal-to noise ratio of the photocathode can The signal-to noise ratio of the photocathode can be calculated asbe calculated as
SNR = [N x P/(1 - P)]SNR = [N x P/(1 - P)]1/21/2
For example, if N = 1 (single impinging For example, if N = 1 (single impinging photon):photon):
PP 0.10.1 0.30.3 0.90.9
SNRSNR 0.330.33 0.650.65 33
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
P 0.1 0.3 0.9
SNR 1.5 2.9 13.4
SNR = [N x P/(1 - P)]SNR = [N x P/(1 - P)]1/21/2
For N = 20 impinging photons:
Signal to noise ratio
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Light conversion into a measurable
Visible light can react and become measurable by:Visible light can react and become measurable by: Eye Eye (human: QE ~ 3 % &(human: QE ~ 3 % & animal), plants, animal), plants,
paints,... paints,... Photoemulsion Photoemulsion (QE ~ 0.1 – 1 %)(QE ~ 0.1 – 1 %) (photo- (photo-
chemical)chemical) Photodiodes (photoelectrical, evacuated)Photodiodes (photoelectrical, evacuated)
Classical & hybrid photomultipliers Classical & hybrid photomultipliers (QE ~ 25 (QE ~ 25 %)%)
QE ~ 45 % (HPD with GaAsP photocathode)QE ~ 45 % (HPD with GaAsP photocathode) PhotodiodesPhotodiodes (QE ~ 70 – 80 %)(QE ~ 70 – 80 %) (photoelectrical)(photoelectrical)
PIN diodes, Avalanche diodes, SiPM,...PIN diodes, Avalanche diodes, SiPM,... photodiode arrays like CCD, CMOS photodiode arrays like CCD, CMOS
cameras,...cameras,...
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Short Historical Excursion 1889: Elster and Geitel discovered that in alkali
metals a photo-electric effect can be induced by visible light (the existence of the e- was yet unknown)
1905: Einstein put forward the concept that photoemission is the conversion of a photon into a free e-
Until ~1930 QE of available materials was < 10-4
1929: discovered Ag-O-Cs photo-emitter (Koller; Campbell) improved the QE to the level of ~ 10-2
1st important application: reproduce sound for film
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Short Historical Excursion Improved materials were discovered later on but it Improved materials were discovered later on but it
was a combination of a good luck with „intelligent was a combination of a good luck with „intelligent guessing“guessing“
A very important step was to realize that the A very important step was to realize that the photocathode materials are SEMICONDUCTORSphotocathode materials are SEMICONDUCTORS
MetallicMetallic versus versus Nonmetallic Nonmetallic materials: materials: yield of metallic photocathodes is very low yield of metallic photocathodes is very low
because of very high reflectivitybecause of very high reflectivity semiconductors have less reflection lossessemiconductors have less reflection losses
The main loss process in metals is the e- The main loss process in metals is the e- scattering; => e- escape depth of only few atomic scattering; => e- escape depth of only few atomic layers is possiblelayers is possible
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Short Historical Excursion
The losses in Semiconductors because of The losses in Semiconductors because of phonon scattering (interaction with lattice) are phonon scattering (interaction with lattice) are much less, i.e. e- from deeper layers can reach much less, i.e. e- from deeper layers can reach the surface the surface
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Short Historical ExcursionMetalMetal SemiconductSemiconduct
oror
Photon Photon e- e-
conversionconversionHigh High reflectivityreflectivity
Low efficiencyLow efficiency
Low reflectivityLow reflectivity
High efficencyHigh efficency
e- motione- motion Low efficiency:Low efficiency:
e- e- scatteringe- e- scatteringHigh efficiencyHigh efficiency
low phonon low phonon lossloss
Surface barrierSurface barrier Work functionWork function
> 2 eV> 2 eVDetermined by Determined by e- affinitye- affinity
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Short Historical Excursion
19101910: Photoelectric effect on K-Sb compound : Photoelectric effect on K-Sb compound was found (Pohl & Pringsheim).was found (Pohl & Pringsheim).
19231923: found that thermionic emission of W is : found that thermionic emission of W is greatly enhanced when exposed to Cs vapour greatly enhanced when exposed to Cs vapour (Kingdon & Langmuir). (Kingdon & Langmuir).
It was found that the work function in the It was found that the work function in the above case was lower than of Cs metal in bulk.above case was lower than of Cs metal in bulk.
19361936: discovered high efficiency of Cs-Sb : discovered high efficiency of Cs-Sb (Görlich).(Görlich).
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of Metals
For photon energies > 12 eV QE of 1-10 % For photon energies > 12 eV QE of 1-10 % were reported for were reported for
NiNi, , CuCu, Pt, , Pt, AuAu, W, Mo, Ag and Pd , W, Mo, Ag and Pd
(1953, Wainfan). (1953, Wainfan).
7% for Au @ 15 eV7% for Au @ 15 eV
2% for Al2% for Al @ 17 eV @ 17 eV
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Escape Depth
Escape depth can be defined as the thickness Escape depth can be defined as the thickness above which the photoemission becomes above which the photoemission becomes independent on thickness (in reflective mode)independent on thickness (in reflective mode)
The measured escape depth was 10-20 atomic The measured escape depth was 10-20 atomic layers for K, Rb, Cs (1932).layers for K, Rb, Cs (1932).
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE: Short Historical Excursion
1955-19581955-1958 Sommers found the „multialkali“ Sommers found the „multialkali“ effect: combination of effect: combination of Cs-K-Na-SbCs-K-Na-Sb has high QE has high QE in the visible spectrum.in the visible spectrum.
Also were discoveredAlso were discovered CsCs33SbSb on MnO ( on MnO (S11S11, , peakpeak 400nm, QE ~ 20%) 400nm, QE ~ 20%) (Cs)Na(Cs)Na22KSbKSb ( (S20S20, , peakpeak 400nm, QE ~ 30%) 400nm, QE ~ 30%) KK22CsSbCsSb ( (peakpeak 400nm, QE ~ 30%) 400nm, QE ~ 30%) KK22CsSb(O) (CsSb(O) (peakpeak 400nm, QE ~ 35%) 400nm, QE ~ 35%)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Typical Quantum Efficiencies
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While selecting ¾‘ EMI 9083A PMTs for the HEGRA imaging Cherenkov telescopes in ~1996 I found 3 out of ~200 PMTs that showed very high „corning blue“ value
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Boost of the QE of Bialkali PMTs
In recent seevral years we were intensively In recent seevral years we were intensively working with the well-known PMT working with the well-known PMT manufacturers looking into the possible boost manufacturers looking into the possible boost of the QE of bialkali PMTs. of the QE of bialkali PMTs. Over past 40 years Over past 40 years there was no progres reported.there was no progres reported.
After several iterations success could be After several iterations success could be reported.reported. PMTs with peak QE values in the range of PMTs with peak QE values in the range of
32-35 % became available.32-35 % became available. These QE boosted PMTs are used in the These QE boosted PMTs are used in the
imaging camera of the MAGIC telescopesimaging camera of the MAGIC telescopes
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
How it shall be possible to boost the QE and who is interested in it ? Use of highly purified materials for photo cathode Use of highly purified materials for photo cathode
(provides lower scattering for e(provides lower scattering for e- - (low (low recombination probability)recombination probability) →→ e- kicked out from deeper (top) layers can e- kicked out from deeper (top) layers can
reach photo cathode-vacuum junction reach photo cathode-vacuum junction ¬¬__ and and „jump“ into it („jump“ into it (→→ thicker cathode is possible). thicker cathode is possible).
Optimal tuning of the photo cathode thicknessOptimal tuning of the photo cathode thickness …………of the structure and material compositionof the structure and material composition …………of the anti-reflective layerof the anti-reflective layer …………??
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QE Measuring Device @ MPI
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Test Setup for Parametrising 7-PMT Clusters
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Setup allows in one go (20‘) measuring 1) linearity, 2) afterpulsing, 3) single ph.e. spectra, 4) F-factor, 5) peak-to-valley ratio,
6) gain, 7) HV distribution & 8) doing flat-fielding
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of „champion“ 2´´ PMT from Hamamatsu
Mirzoyan, et al., (2006) (proc. Beaune‘05)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of another 2´´ PMT from Hamamatsu
Hamamatsu made a statement at Beaune-05 conference that by using a new process they are able to produce PMTs with a new process they are able to produce PMTs with peak QE of 33.7 % on average (Yoshizawa, 2005). peak QE of 33.7 % on average (Yoshizawa, 2005).
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of a champion 2´´ PMT from Photonis
According to Photonis the peak QE should have been 38 %; we meaured 34 %
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of a 3´´ PMT from Electron Tubes
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Electron Tubes Optimising the QE of PMTsElectron Tubes Optimising the QE of PMTs
Different batches show Different batches show different behaviour different behaviour
QE is high (~30% !!)QE is high (~30% !!)
Peak @ ~ 350 nmPeak @ ~ 350 nm
Low QE at long Low QE at long (> 450 nm)(> 450 nm)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
PMTs for MAGIC-IPMTs for MAGIC-I
QE by coating with a diffuse scattering layer
Effective QE ~ 15 %
WLSmilky layereffect
(D. Paneque, et al., 2002)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
QE of 3 PMTs (2 Hamamatsu + 1 ET) before and after coating with milky layer
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MAGIC-I imaging camera PMTs (blue) compared to MAGIC-II PMTs (red)
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Peak QE of MAGIC-II PMTs @ 350 nm
<QE> = 32 %
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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M-I Upgrade camera PMTs:peak QE @350nm and QE()
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
<QE> = 33.9 %
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QE of several tested PMTs
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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1.5‘ CTA candidate PMT Hamamatsu R11920-100
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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QE of CTA candidate PMT from Hamamatsu
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Collection Efficiency of the 1.5‘ CTA candidate PMT
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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We (CTA) expect that a similar product will be soon (still during this year) provided by the ET Enterprises
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Maximum Peak QE of 3‘ Photonis PMT
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Minimum Peak QE
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Photonis 3‘
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Peak QE Map Scanned with a ~3mm Beam
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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PMTs with reflective mode photo cathode
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
• Such PMTs can provide higher QE than those with transmission mode cathodes• Although in literature one speaks about a peak QE enhancement of up to x2, in practiceone finds values of ~40%
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Photo cathode light reflection and absorption
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
blue: ETL 9102B; green: ETL 9902B
Motta, Schönert (2005)
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Light-induced afterpulsing
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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2-types of afterpulsing
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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Light-emission microscopy @ MPI
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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PMT light emission
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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The higher QE @ corners are due to the mirror reflection
29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Other strongly competing ultra-fast,LLL sensors with single ph.e. resolution
Two types of ultra-fast response LLL sensors, providing Two types of ultra-fast response LLL sensors, providing good single ph.e. resolution, start to strongly compete with good single ph.e. resolution, start to strongly compete with the classical PMTs.the classical PMTs.
These are These are HPDs with GaAsP photocathodeHPDs with GaAsP photocathode SiPM (and its variations) SiPM (and its variations)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
18-mm GaAsP HPD (R9792U-40) (development started in our group ~17 years ago)
Designed for MAGIC-II telescope camera; (developed with Hamamatsu Photonics )
(expensive)
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
SiPM: making its own way
MEPhI-MPI-EXCELITAS
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
SiPM: making its own way: the mean number of measured ph.e. is 96
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
Conclusions
In recent years on our request the main In recent years on our request the main PMT manufacturers have been working PMT manufacturers have been working on boosting the QE of classical PMTson boosting the QE of classical PMTs
As a result bialkali PMTs of 1-3´´ size with As a result bialkali PMTs of 1-3´´ size with ~ 35 % peak QE („superbialkali“) became ~ 35 % peak QE („superbialkali“) became commercially available (~ 40% boost!) commercially available (~ 40% boost!)
The PMTs continue becoming better and The PMTs continue becoming better and betterbetter
The last word is not yet saidThe last word is not yet said
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29th of June 20012, Univ. Chicago
Razmik Mirzoyan, Max-Planck-Munich: Highest QE PhotoCathodes
HPD Output Signal
<pulse height distribution>
<pulse shape>
FWHM ~ 2.7 ns
Time [ns]0 2 4 6 8 10 12 14 16
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