IceCube Optical Module OM:

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IceCube Optical Module (OM) Improvement of the
Photon Collection Efficiency
Lutz Köpke, Uni-Mainz Rolf Nahnhauer,
DESY-Zeuthen Elisa Resconi, DESY-Zeuthen/MPIK-Heid
elberg In-Ice Hardware Meeting Madison, August
2002
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Outline - 1 - Light transmission of AMANDA
OMs - 2 - Possible improvements - 2.1 -
Optimization of OM Components - 2.1.1 - OM
glass - 2.1.2 - Optical coupling gel -
2.1.3 - PMT glass and photocatode - 2.2 -
Wavelength shifter - 3 - Analysis of different
scenarios
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-1 - Light transmission of AMANDA OMs
Cherenkov- Spectrum (200-600 nm)
OM Glass
Type Benthos I sphere used for this
estimation Thickness 11-12 mm transmission
probability 30
Coupling Gel
Type RTV 6156 (GE Silicones) Thickness 5 - 20
mm transmission of residual photons 5
mm 97.5 20 mm 90
PMT Glass
Type borosilicate glass Thickness
2.7 mm transmission of residual photons
81
PMT Cath.
Type Bialkali quantum efficiency (QE) 25

Photo-electrons / Cher. photons 6
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-2- Possible Improvements

• WaveLength Shifter (WLS)
• Dedicated RD on going _at_ MPIK-Heidelberg
  (supported by DESY and EU commission)
• cf. E. Resconi talks in Berkeley and Stockholm
  general meeting.
• Plastic WLS window outside the OM
• - Pro no big impact on OM design
• and production
• Cons
• still in RD phase
• new component outside the OM
• long term stability tests to be performed.

• Optimization of OM Components
• Dedicated RD ongoing in Mainz
• cf. L. Köpke talks in Berkeley and
• Stockholm general meeting.
• - Pro advanced status of research
• Cons all OM-components to be
• optimized
• -OM glass
• -Optical Coupling Gel
• -PMT glass.

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-2.1.1- Optimization of OM components OM Glass
Schott
Benthos
50 threshold 295 nm (standard iron-poor
Borosilicate) 50 threshold 335 nm or 355
nm Extremely low radioactivity components 500 Hz
rate, better than standard (but U-leakage from
lining problematic!) low-K
Schott Industrial process only one (two) can
be ordered in smaller batches production
cycles Cost 2-3 times as Benthos? (maybe use
cheaper glass for back)
Low potassium spheres have same hardness as
standard spheres
Schott has 9 months lead time, production
(probably only in fall) Schott can not produce
sample pressure spheres due to technical
reasons find different company using Schott
glass?
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-2.1.2- Optimization of OM components Optical
Coupling Gel
References 1 Peter Sudhoff, AMANDA IR 2
Elisa Resconi, Internal Note 3 Lutz Koepke,
Talk Berkeley General Meeting 4 Rolf Nahnhauer,
Talk Berkeley General Meeting 5 GE Silicones,
Data sheet 6 WACKER, Data sheet
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-2.1.3- Optimization of OM components PMT
Glass transmittance got worse with time!
Hamamatsu willing to use glass of
other manufacturers (e.g. SCHOTT)
... important UV-transparency correct
thermal expansion
E. Lorentz demand for PMTs in future higher
than capabilities of PMT-makers search for
glass manufacturers (TV-bulb industry?) on the way
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-2.2- Possible Improvement Wavelength Shifter
Cherenkov-Spectrum (200-600 nm)
Wavelength shifter thin plastic film (PMP)
Direct photons
Wavelength
310 nm
200 nm
26 Cher. light abs. re-emitted vs PMT
direction
OM Glass
Gel
Transm. Prob. 81.0 30.0
PMT Glass
Transm. of residual photons 10 mm
95.0 94.9
PMT Cath.
Transm. of residual photons 91.0 81.0
QE 25.0 25.0
photo-electrons ONLY from WLS 4.5
photo-electrons from direct phot. 6.0
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-3- Analysis of Different Scenarios