Mirzoyan VH QE PMT Chicago by fYX8HZg

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									Highest QE‘s Measured So Far
           Razmick Mirzoyan,

       Max-Planck-Institute for Physics
             Munich, Germany
                  Quantum Efficiency
   Quantum efficiency (QE) of a sensor is defined as
    the ratio
               QE = N(ph.e.) : N(photons)
   Conversion of a photon into ph.e. is a purely
    binomial process (and not poisson !)
      Assume N photons are impinging onto a
       photocathode and every photon has the same
       probability P to kick out a ph.e..
       Then the mean number of ph.e.s is N x P and
       the Variance is equal to N x P x (1 – P)

    29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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    Univ. Chicago         Munich: Highest QE PhotoCathodes
Differences between binomial
  and poisson distributions




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
                        Signal to noise ratio
The signal-to noise ratio of the photocathode can be
calculated as
                                                               1/2
                  SNR = [N x P/(1 - P)]
   For example, if N = 1 (single impinging photon):


                    P       0.1         0.3         0.9

                    SNR     0.33       0.65           3


  29th of June 20012,        Razmik Mirzoyan, Max-Planck-
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  Univ. Chicago             Munich: Highest QE PhotoCathodes
                 Signal to noise ratio

                                                           1/2
                 SNR = [N x P/(1 - P)]
                 For N = 20 impinging photons:



                  P      0.1        0.3         0.9

                  SNR    1.5        2.9        13.4


29th of June 20012,      Razmik Mirzoyan, Max-Planck-
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Univ. Chicago           Munich: Highest QE PhotoCathodes
                 Light conversion into a
                       measurable
   Visible light can react and become measurable by:
      Eye (human: QE ~ 3 % & animal), plants, paints,...

      Photoemulsion (QE ~ 0.1 – 1 %) (photo-chemical)

      Photodiodes (photoelectrical, evacuated)

         Classical & hybrid photomultipliers (QE ~ 25 %)

          QE ~ 45 % (HPD with GaAsP photocathode)
       Photodiodes (QE ~ 70 – 80 %) (photoelectrical)
              PIN diodes, Avalanche diodes, SiPM,...
              photodiode arrays like CCD, CMOS cameras,...

        29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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        Univ. Chicago         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

29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Short Historical Excursion
   Improved materials were discovered later on but it
    was a combination of a good luck with „intelligent
    guessing“
   A very important step was to realize that the
    photocathode materials are SEMICONDUCTORS
   Metallic versus Nonmetallic materials:
      yield of metallic photocathodes is very low
       because of very high reflectivity
      semiconductors have less reflection losses

    The main loss process in metals is the e-
    scattering; => e- escape depth of only few atomic
    layers is possible
29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Short Historical Excursion
   The losses in Semiconductors because of phonon
    scattering (interaction with lattice) are much less,
    i.e. e- from deeper layers can reach the surface




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
   Short Historical Excursion
                                Metal                   Semiconductor


Photon  e-              High reflectivity Low reflectivity
conversion               Low efficiency    High efficency
e- motion                Low efficiency:              High efficiency
                         e- e- scattering             low phonon loss

Surface barrier          Work function                Determined by
                         > 2 eV                       e- affinity
   29th of June 20012,      Razmik Mirzoyan, Max-Planck-
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   Univ. Chicago           Munich: Highest QE PhotoCathodes
Short Historical Excursion
   1910: Photoelectric effect on K-Sb compound was
    found (Pohl & Pringsheim).
   1923: found that thermionic emission of W is
    greatly enhanced when exposed to Cs vapour
    (Kingdon & Langmuir).
   It was found that the work function in the above
    case was lower than of Cs metal in bulk.
   1936: discovered high efficiency of Cs-Sb (Görlich).



29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
QE of Metals
   For photon energies > 12 eV QE of 1-10 % were
    reported for

    Ni, Cu, Pt, Au, W, Mo, Ag and Pd
    (1953, Wainfan).

   7% for Au @ 15 eV

   2% for Al @ 17 eV

29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Escape Depth
   Escape depth can be defined as the thickness above
    which the photoemission becomes independent on
    thickness (in reflective mode)

   The measured escape depth was 10-20 atomic
    layers for K, Rb, Cs (1932).




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
QE: Short Historical Excursion
   1955-1958 Sommers found the „multialkali“ effect:
    combination of Cs-K-Na-Sb has high QE in the
    visible spectrum.
   Also were discovered
      Cs3Sb on MnO (S11, lpeak 400nm, QE ~ 20%)

      (Cs)Na2KSb     (S20, lpeak 400nm, QE ~ 30%)
      K2CsSb              (lpeak 400nm, QE ~ 30%)
      K2CsSb(O)           (lpeak 400nm, QE ~ 35%)


29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
  Typical Quantum Efficiencies




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,    Razmik Mirzoyan, Max-Planck-
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  Univ. Chicago         Munich: Highest QE PhotoCathodes
Boost of the QE of Bialkali PMTs
    In recent seevral years we were intensively
     working with the well-known PMT manufacturers
     looking into the possible boost of the QE of bialkali
     PMTs. Over past 40 years there was no progres
     reported.
    After several iterations success could be reported.
       PMTs with peak QE values in the range of 32-
        35 % became available.
       These QE boosted PMTs are used in the
        imaging camera of the MAGIC telescopes


 29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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 Univ. Chicago         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
    (provides lower scattering for e- (low
    recombination probability)
      → e- kicked out from deeper (top) layers can
       reach photo cathode-vacuum junction ¬_ and
       „jump“ into it (→ thicker cathode is possible).
   Optimal tuning of the photo cathode thickness
   ……of the structure and material composition
   ……of the anti-reflective layer
   ……?
29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
              QE Measuring Device @ MPI




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
       Test Setup for Parametrising 7-PMT Clusters




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
       29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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       Univ. Chicago         Munich: Highest QE PhotoCathodes
QE of „champion“ 2´´ PMT from Hamamatsu

                                             Mirzoyan, et al., (2006)
                                             (proc. Beaune‘05)




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         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 peak QE
of 33.7 % on average (Yoshizawa, 2005).




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         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 %




29th of June 20012,       Razmik Mirzoyan, Max-Planck-
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Univ. Chicago            Munich: Highest QE PhotoCathodes
         QE of a 3´´ PMT from Electron Tubes




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Electron Tubes Optimising the QE of PMTs

                                      Different batches show
                                       different behaviour

                                      QE is high (~30% !!)

                                      Peak @ ~ 350 nm

                                      Low QE at long l
                                       (> 450 nm)

29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
     PMTs for MAGIC-I

                                        QE  by coating with a
                      milky              diffuse scattering layer
WLS                   layer                             (D. Paneque, et al., 2002)
                      effect




                                               Effective QE  ~ 15 %
29th of June 20012,       Razmik Mirzoyan, Max-Planck-
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Univ. Chicago            Munich: Highest QE PhotoCathodes
QE of 3 PMTs (2 Hamamatsu + 1 ET) before
and after coating with milky layer




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
MAGIC-I imaging camera PMTs (blue)
compared to MAGIC-II PMTs (red)




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Peak QE of MAGIC-II PMTs @ 350 nm




                                                    <QE> = 32 %




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
M-I Upgrade camera PMTs:
peak QE @350nm and QE(l)

                                                 <QE> = 33.9 %




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
QE of several tested PMTs




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
1.5‘ CTA candidate PMT
Hamamatsu R11920-100




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
QE of CTA candidate PMT from Hamamatsu




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Collection Efficiency of the 1.5‘
CTA candidate PMT




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
We (CTA) expect that a similar product will
be soon (still during this year) provided by the
ET Enterprises




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
  Maximum Peak QE of 3‘ Photonis PMT




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
                      Minimum Peak QE

                                                           Photonis 3‘




29th of June 20012,      Razmik Mirzoyan, Max-Planck-
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Univ. Chicago           Munich: Highest QE PhotoCathodes
 Peak QE Map Scanned with a ~3mm Beam




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
PMTs with reflective mode photo cathode

                                                         • 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 practice
                                                         one finds values of
                                                         ~40%
29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Photo cathode light reflection and absorption

                         Motta, Schönert (2005)




                      blue: ETL 9102B; green: ETL 9902B


29th of June 20012,           Razmik Mirzoyan, Max-Planck-
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Univ. Chicago                Munich: Highest QE PhotoCathodes
Light-induced afterpulsing




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
2-types of afterpulsing




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
Light-emission microscopy @ MPI




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
PMT light emission




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
The higher QE @ corners are due to the
mirror reflection




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         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
    good single ph.e. resolution, start to strongly compete with
    the classical PMTs.
   These are
      HPDs with GaAsP photocathode

      SiPM (and its variations)




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         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)
29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
           SiPM: making its own way

                                             MEPhI-MPI-EXCELITAS




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
      SiPM: making its own way:
the mean number of measured ph.e. is 96




29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
                      Conclusions
   In recent years on our request the main
    PMT manufacturers have been working on
    boosting the QE of classical PMTs
   As a result bialkali PMTs of 1-3´´ size with
    ~ 35 % peak QE („superbialkali“) became
    commercially available (~ 40% boost!)
   The PMTs continue becoming better and
    better
   The last word is not yet said

29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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Univ. Chicago         Munich: Highest QE PhotoCathodes
                HPD Output Signal
                                 <pulse height distribution>
    <pulse shape>




0 2 4 6 8 10 12 14 16
         Time [ns]

  FWHM~2.7 ns
     29th of June 20012,    Razmik Mirzoyan, Max-Planck-
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     Univ. Chicago         Munich: Highest QE PhotoCathodes

								
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