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Line 26: − === Hardware ===+ Line 33:
Line 33: − ==== Dark Box Construction ====+ Line 55:
Line 55: − ==== Light Pulser ====+ Line 61:
Line 61: − ===== Choice of Light Source =====+ Line 67:
Line 67: − === Data Acquisition ===+ Line 75:
Line 75: − == SiPM Measurements ==+ − === Analysis Approach ===+ Line 93:
Line 93: − === Summary of Basic Characteristics and Comparison of SiPMs ===+ Line 115:
Line 115: − === Detailed Characterization ===+ Line 125:
Line 125: − ==== Histogram Fitting Method ====+ Line 157:
Line 157: − ==== Results ====+ Line 181:
Line 181: − == Links ==+ Line 191:
Line 191: − == References ==+
no edit summary
= Bench Test Setup =
= Bench Test Setup =
== Hardware ==
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 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.
=== 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 discreet 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.
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 discreet 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.
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=== 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]]
[[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.
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. The calibrating this device with the HPD showed a very long decay of its pulse. Several more devices with larger wavelengths were procured and measured settling on a yellow LED (Fairchild MV8304) for its speed. The SiPMs were characterized with respect to one another and the HPD using this device. With a mean wavelength of about 590nm, this LED is near the peak of the SiPM detection spectra.
The original LED available to the group was the blue QT Optoelectronics MV5B60. The calibrating this device with the HPD showed a very long decay of its pulse. Several more devices with larger wavelengths were procured and measured settling on a yellow LED (Fairchild MV8304) for its speed. The SiPMs were characterized with respect to one another and the HPD using this device. With a mean wavelength of about 590nm, this LED is near the peak of the SiPM detection spectra.
By the time more detailed studies of the SSPM-06~ were initiated a fast enough device very close the the mean emission wavelength of the BCF-20 was found. This was the Agilent (Avago Technologies) HLMP-CE30-QTC00. It's time width is somewhat larger than the convenient 100ns window that is convenient for data acquisition (explained below), but accurate data can be derived by centering the window at the same spot for every trial.
By the time more detailed studies of the SSPM-06~ were initiated a fast enough device very close the the mean emission wavelength of the BCF-20 was found. This was the Agilent (Avago Technologies) HLMP-CE30-QTC00. It's time width is somewhat larger than the convenient 100ns window that is convenient for data acquisition (explained below), but accurate data can be derived by centering the window at the same spot for every trial.
== Data Acquisition ==
A Tektronix TDS 2024 (2Gsmp/s, 200MHz) is used to acquire the SiPM signal from its [[SiPM_Amplifier|preamplifier]], the response of which 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. 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 resolved to just collect the first 1000 samples, corresponding to the first 4 divisions on the screen. The waveforms now trickled at one per second.
A Tektronix TDS 2024 (2Gsmp/s, 200MHz) is used to acquire the SiPM signal from its [[SiPM_Amplifier|preamplifier]], the response of which 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. 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 resolved to just collect the first 1000 samples, corresponding to the first 4 divisions on the screen. The waveforms now trickled at one per second.
Aside from the convenience of usable results within hours instead of a day, is the issue of avoiding systematic drifts. It was found that while higher statistics smooth out the histogram of integrals, there are also drifts, 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 photon peaks. So, faster data acquisition also meant avoiding these drifts.
Aside from the convenience of usable results within hours instead of a day, is the issue of avoiding systematic drifts. It was found that while higher statistics smooth out the histogram of integrals, there are also drifts, 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 photon peaks. So, faster data acquisition also meant avoiding these drifts.
= SiPM Measurements =
== Analysis Approach ==
[[Image:PhotonPeaks_SSPM05.png|frame|Illustration of discrete peaks seen in the collected SiPM charge frequency histogram. The first peak shows the number of events in which no photons were detected, the next shows one and so forth. Note the even spacing of the peaks, showing the linearity of the device.]]
[[Image:PhotonPeaks_SSPM05.png|frame|Illustration of discrete peaks seen in the collected SiPM charge frequency histogram. The first peak shows the number of events in which no photons were detected, the next shows one and so forth. Note the even spacing of the peaks, showing the linearity of the device.]]
Efficiency calculated in the manner described is compared to the expected efficiency. Integrating the HPD response function in the frequency space weighted by the LED emission spectrum yields the mean detection efficiency of the HPD for that light source. Doing the same with the manufacturer-supplied response function of the SiPM and comparing to the figure for the HPD yields the expected SiPM efficiency relative to the HPD.
Efficiency calculated in the manner described is compared to the expected efficiency. Integrating the HPD response function in the frequency space weighted by the LED emission spectrum yields the mean detection efficiency of the HPD for that light source. Doing the same with the manufacturer-supplied response function of the SiPM and comparing to the figure for the HPD yields the expected SiPM efficiency relative to the HPD.
== Summary of Basic Characteristics and Comparison of SiPMs ==
Below is the summary of results obtained from these measurements performed on the two SiPMs acquired from Photonique.
Below is the summary of results obtained from these measurements performed on the two SiPMs acquired from Photonique.
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== Detailed Characterization ==
Since the SiPM performance is sensitive to the bias voltage applied and the ambient temperature, a measurement SiPM properties as functions of bias voltage (V<sub>b</sub>) and temperature (T) was performed on the SSPM-06~. (By this point, the SSPM-06~ was judged to be a better sensor for the tagger microscope, owing to [[:Image:Image:BCF20,LED,SiPMs comp.png|higher sensitivity in the blue-green range]] and better active area match to the fiber cross-section. Aside from gains in efficiency and dynamic range of the resulting readout, higher photon detection implies better time resolution because of the scintillation decay time of 2.7ns in the fiber.)
Since the SiPM performance is sensitive to the bias voltage applied and the ambient temperature, a measurement SiPM properties as functions of bias voltage (V<sub>b</sub>) and temperature (T) was performed on the SSPM-06~. (By this point, the SSPM-06~ was judged to be a better sensor for the tagger microscope, owing to [[:Image:Image:BCF20,LED,SiPMs comp.png|higher sensitivity in the blue-green range]] and better active area match to the fiber cross-section. Aside from gains in efficiency and dynamic range of the resulting readout, higher photon detection implies better time resolution because of the scintillation decay time of 2.7ns in the fiber.)
However, it was found that the peaks were very indistinct at bias voltages below 20V and temperatures above 20°C. This was probably due to the narrowing of the peaks due to smaller gain or convolution of the additional dark counts detected.
However, it was found that the peaks were very indistinct at bias voltages below 20V and temperatures above 20°C. This was probably due to the narrowing of the peaks due to smaller gain or convolution of the additional dark counts detected.
=== Histogram Fitting Method ===
The solution to this was to abandon the manual location of pedestals, peak spacing etc. Instead, a model was created by Prof. Richard Jones based on which fitting of the histograms was performed. It has the form:
The solution to this was to abandon the manual location of pedestals, peak spacing etc. Instead, a model was created by Prof. Richard Jones based on which fitting of the histograms was performed. It has the form:
Now, with this powerful instrument at hand used with a fitter in Paw, the histograms collected as function of T and V<sub>b</sub> were analyzed. It turned out that even histograms with nearly indistinguishable peaks yielded a best fit to this model and suggested the appropriate gain and other parameters.
Now, with this powerful instrument at hand used with a fitter in Paw, the histograms collected as function of T and V<sub>b</sub> were analyzed. It turned out that even histograms with nearly indistinguishable peaks yielded a best fit to this model and suggested the appropriate gain and other parameters.
=== Results ===
Below is the analyzed data on dark rate, gain and photon detection efficiency (PDE) as function of T and V<sub>b</sub>. An attempt was also made at mapping the rate of secondaries (multi-Poisson parameter) as a function of these variables but the small trends perceived in the data were within the parameter's error bars.
Below is the analyzed data on dark rate, gain and photon detection efficiency (PDE) as function of T and V<sub>b</sub>. An attempt was also made at mapping the rate of secondaries (multi-Poisson parameter) as a function of these variables but the small trends perceived in the data were within the parameter's error bars.
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= Links =
* [[SiPM Vendors]]
* [[SiPM Vendors]]
* [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_Rev1.pdf] and SSPM-06~ [http://www.photonique.ch/DataSheets/SSPM_0606BG4MM_PCB_vs1.pdf]
= References =
# I. Senderovich and R.T. Jones, "Suitability of Silicon Photomultiplier Devices for Readout of a Scintillating Fiber Tagger Hodoscope", ''GlueX-doc-760'' (2007) [http://zeus.phys.uconn.edu/halld/bltwghome/UConn-Jlab_contract-2006/report-2-2007.pdf]
# I. Senderovich and R.T. Jones, "Suitability of Silicon Photomultiplier Devices for Readout of a Scintillating Fiber Tagger Hodoscope", ''GlueX-doc-760'' (2007) [http://zeus.phys.uconn.edu/halld/bltwghome/UConn-Jlab_contract-2006/report-2-2007.pdf]