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Line 32: − == Hardware ==+ − + − It is also preferred that the light source is fast and close in wavelength to the light from scintillating fibers, which are in the blue-green.+ − − − === Dark Box Construction === − − Running this setup with a hybrid photodiode (HPD) module DEP PP0350 of [[:Image:S20photocathode_QE.jpg | known characteristics]] allows us to calibrate the light intensity. The SiPM detection efficiency can then be characterized relative to the HPD. The signal from the SiPM was clean enough to distinguish peaks corresponding to discrete photon (pixel) counts in the histogram signal integrals. Therefore, the gain of the SiPM was found independently of the HPD - the SiPMs were self-calibrating! The [[#SiPM_Measurements|measurements section]] below describes this feature further. − − Below are the diagrams of the dark box with the HPD and SiPM assemblies installed. A temperature controller system (TE Tech. [http://www.tetech.com/temp/tc24-12.shtml TC-24-12]) was procured, which operates by driving a Peltier junction based on feedback from a thermistor compared to voltage-specified reference temperature. It was [[:media:Tc2412calib.pdf|calibrated]] and [[:Image:TempControllerMounted.jpg|installed into the wall]] of the dark box via a custom-designed light-tight frame. − − {| border="0" − |- − |[[Image:DarkboxDiagram_HPD.png]] − |- − | Diagram of the dark box with the HPD module installed. V<sub>HV</sub> = -12 kV, V<sub>b</sub> = 60 V. ±5 V provide the supply rails for the amplifier built into the HPD module. − |- − | − |- − | [[Image:DarkboxDiagram_SiPM.png]] − |- − | Diagram of the dark box with a SiPM mounted on a temperature-controlled cold plate. V<sub>b</sub> is the bias voltage discussed below, V<sub>s</sub> is the preamplifier supply voltage set to 5 V in our work (recommended levels: 4 - 9 V)]] Note that the preamplifier electronics are mounted right on the cold plate extensions to minimize the length of the wires between the the SiPM and preamp input. Other arrangements caused significantly more pickup. − |- − |} − <br> − − === Light Pulser === − − [[Image:PulserCircuit.png|frame|A pulser circuit designed to drive the LED for photo-detector bench tests. The circuit differentiates the input signal, thus the amplitude of the input square wave controls pulse amplitude up to the saturation point, at which the pulse shape broadens to a maximum of 6 ns. V<sub>s</sub> = 5 V]] − − A pulser circuit was designed with a pulse height controlled by the amplitude of a step function from a function generator. The pulser differentiates the step function signal and therefore can create pulses as narrow as the rising edge of the step function. Above a saturation point, the pulse broadens to a maximum of 6 ns. The adjacent figure shows the pulser circuit that drives the LED. The LED has some finite rise time and sometimes a very long decay tail. This response function convolves the pulser signal so the speed of the combined system has to be analyzed for each LED type and evaluated for the use of photon detector characterization. − − ==== Choice of Light Source ==== − − The original LED available to the group was the blue QT Optoelectronics MV5B60. Analyzing the pulses from the HPD illuminated with this device showed an initial spike in its light output followed by a tail with a very long decay constant. Several more devices with longer wavelengths were procured and measured. We settled on a yellow LED (Fairchild MV8304) for subsequent measurements because it had no long tail in its light pulses. The SiPMs were characterized with respect to one another and the HPD using this LED. Its mean wavelength is about 590nm, near the peak of the SiPM photon detection efficiency curve. − − By the time more detailed studies of the SSPM-06 were initiated, a fast LED very close the the mean emission wavelength of the BCF-20 was found. This was the Agilent (Avago Technologies) HLMP-CE30-QTC00. Its pulse shows a small tail in the light output that lasts for about 100ns, but this is fast enough to be contained in the 100ns integration gate used for these tests. − − == Data Acquisition == − − A Tektronix TDS 2024 (2Gsamp/s, 200MHz) was used to acquire the SiPM signal from its [[SiPM_Amplifier|preamplifier]]. The response of the SiPM preamplier is well understood based on detailed [[MATLAB amplifier in detail|analysis and simulation]]. Since tens of thousands of waveforms are necessary to construct a clean histogram of collected charge, a fast PC based data collection system was necessary. The data export module installed on this oscilloscope allows RS-232 interface over which commands can be issued and data transfer requested. Unfortunately going above the baud rate of 9600 always resulted in lost bytes. At 9600 the 2500-sample waveform collected by the oscilloscope takes about 2-3 seconds to transfer over the serial link to the host PC. Since we are dealing with time windows of 1μs in which the unit is too slow to collect all 2500 samples (it was found to copy or interpolate between actual samples) it was decided to just collect the first 1000 samples, corresponding to the first 4 divisions on the screen. Under these conditions, the waveforms were collected at a rate of one per second. − − For the purposes of collecting integrals of waveforms (proportional to total charge collected per received flash) it was later found that the averages of the functions could be automatically computed by the oscilloscope and then the results transferred much faster than the entire waveform, about 3 per second. This value times the window duration equals the desired integral! − − Aside from the convenience of being able to collect usable results within hours instead of a day, this speedup also minimized the problem of systematic drifts that occur during long runs. It was found that the higher statistics obtained during extended runs would sometimes be offset by the blurring of peaks due to slow drifts in the gain and pedestal. Whether due to environmental variations over the course of a day or electronic effects, these drifts smeared the histograms, most of which already had a very faint sign of resolved photon peaks. So, faster data acquisition also meant reducing the effects of these drifts. Line 193:
Line 152: − <|colspan="2" | Pulse height spectrum at fixed pulser intensity and temperature 25°C, and increasing bias voltage V<sub>b</sub> = 69.5V (upper left), 70.0V (upper right), 70.2V (lower left), and 71.0V (lower right).+ Line 199:
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Line 220: − Written and last edited by [[User:Senderovich|Igor Senderovich]] 18:30, 13 August 2007 (EDT)+
no edit summary
= SiPM Performance Requirements =
= SiPM Performance Requirements =
[[Image:SSPM05_(1x1).jpg|thumb|370px|SSPM-050701GR-TO18 [http://www.photonique.ch/DataSheets/SSPM_050701GR_TO18_Rev1.pdf] from [http://www.photonique.ch Photonique SA], with 1 mm<sup>2</sup> active area with 556 pixels]]
[[Image:SSPM05_(1x1).jpg|thumb|226px|SSPM-050701GR-TO18 [http://www.photonique.ch/DataSheets/SSPM_050701GR_TO18_Rev1.pdf] from [http://www.photonique.ch Photonique SA], with 1 mm<sup>2</sup> active area with 556 pixels]]
[[Image:SSPM06_(2x2).jpg|thumb|370px|SSPM-0606BG4-PCB [http://www.photonique.ch/DataSheets/SSPM_0606BG4MM_PCB_vs1.pdf] from [http://www.photonique.ch Photonique SA], with 4.4 mm<sup>2</sup> active area with 1700 pixels]]
[[Image:SSPM06_(2x2).jpg|thumb|226px|SSPM-0606BG4-PCB [http://www.photonique.ch/DataSheets/SSPM_0606BG4MM_PCB_vs1.pdf] from [http://www.photonique.ch Photonique SA], with 4.4 mm<sup>2</sup> active area with 1700 pixels]]
[[Image:MPPC050C_(1x1).jpg|thumb|226px|MPPC S10362-11-050C [http://209.73.52.252/assets/pdf/catsandguides/mppc_kapd0002e03.pdf] from [http://sales.hamamatsu.com/en/home.php Hamamatsu], with 1 mm<sup>2</sup> active area with 400 pixels]]
A novel method of low light readout is evaluated here. Traditionally, signals of tens to hundreds of photons are read out by photomultiplier tubes (PMTs), which provide gain of <math>10^6</math> via a cascade of electrons multiplied on collision at each of the device's sequential dynodes. The small cross-section scintillating fibers in the high rate tagger microscope that will operate in Hall-D of Jefferson Lab call for a new and more compact readout. Silicon Photomultipliers (SiPMs) are discussed on the merits of their gain, detection efficiency, speed and noise level.
A novel method of low light readout is evaluated here. Traditionally, signals of tens to hundreds of photons are read out by photomultiplier tubes (PMTs), which provide gain of <math>10^6</math> via a cascade of electrons multiplied on collision at each of the device's sequential dynodes. The small cross-section scintillating fibers in the high rate tagger microscope that will operate in Hall-D of Jefferson Lab call for a new and more compact readout. Silicon Photomultipliers (SiPMs) are discussed on the merits of their gain, detection efficiency, speed and noise level.
The tagger microscope consists of many identical and well isolated readout channels, each
The tagger microscope consists of many identical and well isolated readout channels, each
consisting of a several cm long scintillating fiber connected to a clear acrylic fiber
consisting of a 2 cm scintillating fiber connected to a clear acrylic fiber
light guide.
light guide.
A tagging electron travels axially down the length of a scintillating fiber depositing an average of 4 MeV of energy in the fiber,
A tagging electron travels axially down the length of a scintillating fiber depositing an average of 4 MeV of energy in the fiber,
unusual detection efficiency on the part of the SiPM. For example, 10% efficiency
unusual detection efficiency on the part of the SiPM. For example, 10% efficiency
with the above number of photons still yields a signal of 130 photons. However,
with the above number of photons still yields a signal of 130 photons. However,
given that the scintillator ([http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC%20Scintillating%20Optical%20Fibers%20Brochure%20605.pdf BCF-20])
given that the scintillator ([http://www.detectors.saint-gobain.com/Data/Element/Product/product.asp?ele_ch_id=P0000000000000001909 BCF-20])
has a finite decay time (2.7ns) the more photons are produced the more clearly resolved is the leading-edge time of the pulse.
has a finite decay time (2.7ns) the more photons are produced the more clearly resolved is the leading-edge time of the pulse. (See [[Tagger Time Resolution]])
The device is expected to have a high enough gain (measured in electrons per photon detected) - around 10<sup>6</sup> in order for such a small light signal to be recorded by conventional electronics. SiPM devices are also susceptible to spurious, thermally excited pixel breakdowns, each showing up as a single photon hit ("dark count"). Very high rates of these single-pixel events may create pileup above the signal threshold. All of the above parameters (detection efficiency, gain and dark rate) depend on applied bias voltage and temperature. Stability of performance within the expected fluctuations of these environmental variables is an important requirement.
The device is expected to have a high enough gain (measured in electrons per photon detected) - around 10<sup>6</sup> in order for such a small light signal to be recorded by conventional electronics. SiPM devices are also susceptible to spurious, thermally excited pixel breakdowns, each showing up as a single photon hit ("dark count"). Very high rates of these single-pixel events may create pileup above the signal threshold. All of the above parameters (detection efficiency, gain and dark rate) depend on applied bias voltage and temperature. Stability of performance within the expected fluctuations of these environmental variables is an important requirement.
= Bench Test Setup =
= Bench Test Setup =
A fast light source operating in an environment with little background is necessary for the tests described here. The challenge is in preventing light leaks in this chamber despite the need for access ports, cable feed-through, and a temperature control module that requires heat exchange with the outside.
A fast light source operating in an environment with little background is necessary for the tests described here. The challenge is in preventing light leaks in this chamber despite the need for access ports, patching wires through walls and installing sensor and temperature control modules that must interface with the outside.
A [[dark chamber]] was constructed to create this controlled environment. Please refer to the [[dark chamber | more detailed page]] on its construction, test and calibration.
Additionally a reference sensor is necessary to calibrate the light flux. A UV/Blue/Green-sensitive [[Hybrid Photodiode]] (HPD) from DEP was used for this purpose. It has a detection efficiency of 5-15% in the wavelength range of our light sources and a factor of 2700 gain at the recommended HV of 12 kV. Unfortunately this low gain and its high capacitance (~200 pF) results in statistical charge fluctuations of several photo-electrons, preventing discrete photon counting. However, devices of this type, owing to their simple acceleration gap, have a very predictable gain, consistent from from one unit to the next. Its gain factor was used as an assumption for all subsequent calculations.
= SiPM Measurements =
= SiPM Measurements =
| [[Image:hVb702_T25.gif|250px]] || [[Image:hVb710_T25.gif|250px]]
| [[Image:hVb702_T25.gif|250px]] || [[Image:hVb710_T25.gif|250px]]
|-
|-
|colspan="2" | Pulse height (V-s) spectrum at fixed pulser intensity and temperature 25°C, and increasing bias voltage V<sub>b</sub> = 69.5V (upper left), 70.0V (upper right), 70.2V (lower left), and 71.0V (lower right).
|-
|-
|}
|}
|-
|-
| [[Image:hDVb700_T25.gif|250px]]
| [[Image:hDVb700_T25.gif|250px]]
|Pulse height spectrum with zero pulser intensity and temperature 25°C, and bias voltage V<sub>b</sub> = 70.0V.
|Pulse height (V-s) spectrum with zero pulser intensity and temperature 25°C, and bias voltage V<sub>b</sub> = 70.0V.
|}
|}
The black histograms in the plots are the data and the red curves are the best fit to the data using the multi-Poisson model described in a preceeding section, with two modifications.
The black histograms in the plots are the data and the red curves are the best fit to the data using the multi-Poisson model described in a preceeding section, with two modifications.
* The Gaussian smearing of the individual pixel pulse-height distribution was replaced with the following function that has an asymmetric tail.
* The Gaussian smearing of the individual pixel pulse-height distribution was replaced with the following function that has an asymmetric tail.
{|align="right"
{|align="center"
|<math>f(x;\alpha,\beta,\sigma)</math>||=||<math>\beta\frac{\alpha}{2}\,e^{\alpha x+\frac{\alpha^2\sigma^2}{2}[1-Erf(\frac{x+\alpha\sigma^2}{\sqrt{2}\sigma})] </math>
|<math> \frac{}{}f(x;\alpha,\beta,\sigma) </math> ||=|| <math>(1-\beta)\frac{\alpha}{2}\,e^{\alpha x+\frac{\alpha^2\sigma^2}{2}}\left[1-Erf(\frac{x+\alpha\sigma^2}{\sqrt{2}\sigma})\right] </math>
|-
|-
| || ||<math> + \frac{1-\beta}{\sqrt{2\pi}\sigma}e^{-\frac{x^2}{2\sigma^2}}
| || ||<math> + \frac{\beta}{\sqrt{2\pi}\sigma}\,e^{-\frac{x^2}{2\sigma^2}}
</math>
</math>
|}
|}
: This function is normalized to unity and is described by two parameters:
: This function is normalized to unity and is described by parameters:
:# <math>\alpha</math> = inverse length of left-side tail
:# <math>\beta</math> = fraction of peak integral in left-side tail
:# <math>\sigma</math> = sigma of Gaussian right-side tail = <math> (\sigma_0^2+(p+s)\sigma_1^2)^{1/2}</math>
* The mean cross-talk parameter, formerly <i>p</i>μ in the treatment described above, has been replaced with <i>p</i><sup>2</sup>μ.
Without the second change above, the fit to the data is significantly worse. It might be explained by the tendency of cross-talk to bunch up because of self-coupling feedback. A simpler explanation might be that it takes into account a natural variation in the light output of the pulser from pulse to pulse. This remains to be investigated. The parameters of the fit function listed in the above plots are listed below.
# Integral of fit function, in rescaled (''pe'') x-axis units.
# Centroid of zero ''pe'' peak, in V-s.
# Gain of readout, in V-s/''pe''.
# Mean detected photon count (λ<sub>p</sub>)
# Mean cross-talk pixels per detected photon (λ<sub>s</sub>)
# Excess noise per pixel (σ<sub>1</sub>), in ''pe''
# α parameter of peak shape function, see above
# σ<sub>0</sub> parameter of peak shape function, see above
# β parameter of peak shape function, see above
The Fortran source code where the fit function is implemented can be found [http://zeus.phys.uconn.edu/halld/siliconPM/fits-2-2008/pshape.f here].
==== MPPC measurement to-do list ====
* Increase LED output and compare spectra
* Collect spectra of signal peaks as a function of window position (to evaluate distribution of after-pulses)
* Look for methods/components to boost data collection rate
= Links =
= Links =
* [[SiPM Vendors]]
* [[SiPM Vendors]]
* BCF-20 Scintillating Fiber (catalog) [http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC%20Scintillating%20Optical%20Fibers%20Brochure%20605.pdf]
* [[Tagger Time Resolution]] estimates
* [[:Image:S20photocathode_QE.jpg|Detection spectrum]] of the HPD photocathode.
* BCF-20 Scintillating Fiber (catalog) [http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC_Scintillating_Optical_Fibers_Brochure.pdf]
* [[Hybrid Photodiode]] (HPD)
* [[dark chamber | Photo-sensor Test Stand]]
* Temperature Controller (vendor page) [http://www.tetech.com/temp/tc24-12.shtml]
* Temperature Controller (vendor page) [http://www.tetech.com/temp/tc24-12.shtml]
* Callibration of the temperature controller: a [[:media:Tc2412calib.pdf|lookup table]] for the control and monitor voltage.
* Callibration of the temperature controller: a [[:media:Tc2412calib.pdf|lookup table]] for the control and monitor voltage.
* Brandan Krueger's pages on the [[SiPM Amplifier]] and [[MATLAB amplifier in detail]]
* Brandan Krueger's pages on the [[SiPM Amplifier]] and [[MATLAB amplifier in detail]]
* [http://www.photonique.ch Photonique SA] SiPM Specification Sheets: SSPM-05~ [http://www.photonique.ch/DataSheets/SSPM_050701GR_TO18_Rev1.pdf] and SSPM-06~ [http://www.photonique.ch/DataSheets/SSPM_0606BG4MM_PCB_vs1.pdf]
* [http://www.photonique.ch Photonique SA] SiPM Specification Sheets: SSPM-05~ [http://www.photonique.ch/DataSheets/SSPM_050701GR_TO18.pdf] and SSPM-06~ [http://www.photonique.ch/DataSheets/SSPM_0606BG4MM.pdf]
* [[SiPM Radiation Hardness Tests]]
= References =
= References =
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Last edited by [[User:Senderovich|Igor Senderovich]], June 2008