Jan 20, 2012 Readout

Teleconference Time: 11:00 a.m. EST'

• ESNET (Number is 8542553) and EVO session (GlueX Calorimetry meeting room)
• Phone connection only upon request.
  • +1-866-740-1260 : US+Canada
  • +1-303-248-0285 : International
  • then enter participant code: 3421244# (remember the "#").
  • or www.readytalk.com (and code without the #)

Participant Direct Lines

• JLab Phone: in CC F326 is 757-269-6337 (usual room)
• JLab Phone in CC L207 is 757-269-7084
• Phone in the Regina Videoconference Suite is 306-585-4204
• Athens Phone: in Christina's office is 011-30-210-727-6947

Presentations from recent meetings

1. Update from USM at Bcal Readout Meeting
   • SiPM testing
   • Light guides
   • Station 2 report
   • Production Manager Report
2. Presentations at Cal Working Group Meeting
   • Characterization studies of silicon photomultipliers NIM A620 (2010) 217 (Link for JLab)
   • Key Figure 8
   • PDE measurement update at USM

Tentative Agenda

1. Announcements
2. SiPM PDE extraction at Regina
3. Comparison of PDE measurements in literature (Elton)
4. Comparison of Current vs Rate (Yi)
5. Updates from USM
6. Discussion on qualification of USM setup for production testing
   • Comparison of dark rate, cross talk
   • Thermal contact of SiPMs to cooling plate
   • Insertion and extraction procedures

Minutes

Attending: Mehrnoosh, Andrei, George, Mermoose (UofR); Carl, Yi, Elton, Eugene (JLab); Will, Serguei, Hayk, Remski (USM)

1. Announcements
2. SiPM PDE extraction at Regina
   • Three methods at 460 nm, overvoltage?
   • Measured QE is 17-23%
   • Systematics: Illumination covers the cross macro-fill area (80% of illuminated circle, 89% of SiPM square). All methods include the cross talk (~10%). The first item yields lower PDE, the second yields higher PDE.
   • Will: Inquired about the uniformity of illumination, which could also affect the coverage of the active/dead area
3. Comparison of PDE measurements in literature (Elton)
4. Comparison of Current vs Rate (Yi)
   • Based on comparison of current vs count rates, expects current measurements of PDE to overestimate by about 37%.
5. Updates from USM
   • George gave estimates of PDE based on expected QE, fill factor and avalanche probability. See note below for numbers. Thanks George!
   • Yi inquired about the gain measured when the PDE was measured: Remski said it was 0.55 x 10^6, similar to the JLab measured gain.
   • George: Requested information on the uniformity of parameters across the array
   • Andrei: Asked about the gate used for measurement: 120 ns.
6. Discussion on qualification of USM setup for production testing
   • Will: Goal is for USM to show comparison between JLab/Hamamatsu/USM measurements of all gain, PDE, dark rate, cross talk for all (most) of the 30 first-article samples
   • Data should be ready in a few days
   • Appears to be a normalization discrepancy in the PDE.
   • Discussion will continue on Tuesday at the Bcal Readout meeting.

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e-mail from George:

I looked at the Hamamatsu products web page:

http://sales.hamamatsu.com/index.php?id=13200767

and they list all their SiPM's, where the numbers listed below (common to all of same pixel size) are extracted from:

                        pixel size (μ)                    Fill Factor (%)        
       
                           100 x 100                            78.5
                             50  x   50                            61.5
                             25  x   25                            30.8

Therefore, the "microscopic" FF for our SiPM, which is 50 x 50, is 61.5%. The numbers above also give a clear measure of the dead space between cells by the large loss shown by going to smaller pixels.

Our Hamamatsu calibrated photodiode (same model number as JLab is using) provided us with a table of the spectral sensitivity and QE as a function of wavelength and some of these numbers I am copying below:

                         λ (nm)                      QE (%)

                            460                          61.3
                            480                          62.4
                            500                          62.8
                            520                          63.5

Based on these numbers the QE at 490 nm will be 62.6 %. Such numbers are very representative of the QE of Si used in "optical" devices.

So, if these numbers hold for our devices as well we will get a product of 38.5%. This results in unrealistic values for the avalanche probability. Since the FF is 61.5% and only a much higher QE will raise the PDE to any significant degree and I just don't see such much higher QE values in the literature. Can you point me to a source for the ~ 80% values you quoted?