KETEK GmbH Hofer Str. 3 81737 Munich Germany www.ketek.net info@ketek.net phone +49 89 673 467 70 fax +49 89 673 467 77 Silicon Photomultiplier Evaluation Kit Quick Start Guide Eval Kit
Table of Contents 1 Introduction...3 2 Setup Example...3 3 Single Photon Measurements...4 3.1 Dark Count Spectrum... 4 3.2 Single Photon Spectrum... 4 3.3 Using the Full Dynamic Range... 4 4 Measurements with Scintillator...5 4.1 Energy Spectrum... 5 4.2 Coincidence Time Resolution... 6 5 Appendix...7 5.1 Variant for Optical Bench Mount... 7 5.2 Bias Source... 7 This quick start guide covers the KETEK Evaluation Kit only. For other products please refer to www.ketek.net. Revision history: Rev. 1.0, August 2016 - Initial release
1 Introduction The KETEK Evaluation Kit allows an easy operation and evaluation of any KETEK. It can be used for a wide range of applications which require e.g. single photon counting or measurements with scintillators. Two of the Evaluation Kits can be mounted face to face for coincidence measurements. The Evaluation Kit is equipped with a preamplifier and set up modularly so that the PCBs with the presoldered s can be swapped to a different model. For the operation of the Evaluation Kit only a +12 V DC power supply, a bias source and an oscilloscope are required. For full technical details of the s and the Evaluation Kit, please refer to the KETEK Datasheet and the KETEK Evaluation Kit Datasheet. Additionally, KETEK provides a Bias Source which can be directly connected to the Evaluation Kit. Please refer to the KETEK Bias Source Datasheet for further information. 2 Setup Example The signal and bias connectors are SMA type, the preamplifier is equipped with solder pins. An overview is shown in figure 1. Signal lines need to be be terminated with 50 Ω. Preamplifier power: +12V DC, 150 ma Bias: positive with max. + 40 V, typical current limit 2 ma Signal: connected to the preamplifier Note: Signal corresponds to 90% of the signal Monitor: connected to an oscilloscope (50 Ω DC) Note: Monitor corresponds to 10% of the signal Amplified Signal: connected to an oscilloscope (50 Ω DC) Since the is a highly sensitive photodetector, it must be operated under dark conditions. After biasing the with e.g. 4 V above the breakdown voltage, dark counts should be visible at the Amplified Signal path, using e.g. a timebase of 100 ns/div and a vertical resolution of 20 mv/div. The Monitor is used for higher photon fluxes for which the preamplifier saturates (e.g. when coupling a bright scintillator). Note: The procedure may vary depending on the used readout electronics. For the examples shown here, a digital oscilloscope is used. Fig. 1 Evaluation Kit Connection Scheme +12 V DC GND Monitor Amplified Signal Signal Mounting Holes for Coincidence Setup Bias Preamplifier PCB with 08/2016 Rev. 1.0 Page 3
3 Single Photon Measurements 3.1 Dark Count Spectrum At the oscilloscope, set the trigger to the amplified signal at 0.5 pe amplitude (1 pe is the smallest occurring pulse height, corresponding to a photoelectron pe). Note: This measurement has to be done under dark conditions without illuminating the. Measure the area respectively the charge of the signal at the position of the trigger point in e.g. a 25 ns wide gate. Best results are obtained by integrating the whole positive pulse area. Histogramming of the integrated charge is the resulting dark count spectrum. Note: E.g. crosstalk probability can be extracted from the dark count spectrum. 3.2 Single Photon Spectrum For this measurement, a pulsed light source is needed. This can be e.g. a pulsed LED or a pulsed laser. Connect the electrical trigger output of the pulser to the oscilloscope and set the trigger to it. Note: In case a synchronized electrical trigger output is not provided by the pulser, a second Evaluation Kit can be used to generate the trigger signal. This second should be fully illuminated by the same optical pulse e.g. with an optical beam splitter. The other path for the single photon measurement can be attenuate e.g. with neutral density filters. Measure the area respectively the charge of the signal in e.g. a 25 ns wide gate. The histogram of the measured charge is the single photon spectrum (cf. fig. 2). Note: E.g. the relative gain, breakdown voltage and photo detection efficiency can be extracted. 3.3 Using the Full Dynamic Range The amplified signal output and the Monitor output can be connected and used simultaneously. Typically for low light levels down to single photons, the measurement is done with the amplified output. For higher light levels, the preamplifier will saturate at 0.5 V signal amplitude. After this point, the Monitor output is measured. This allows to exploit the the full dynamic range of the. Fig. 2 Example of a Single Photon Spectrum Measured with PM3350 at 4 V overvoltage Signal 20 mv/div Laser Trigger Signal 5 ns/div Histogram Counts [a.u.] pedestal 1 pe 2 pe 8 pe Start Integration Gate End Integration Gate 9 pe 10 pe 11 pe 3 pe 4 pe 5 pe 6 pe 7 pe 12 pe 13 pe 14 pe 15 pe 16 pe 17 pe Integrated Charge [nvs] Evaluation Kit Quick Start Guide
4 Measurements with Scintillator With bright scintillators typically the charge released by the exceeds the dynamic range of the preamplifier. In this case, the Monitor output is used. The charge released by the is a measure for the detected number of scintillating photons and thus a measure for the deposited energy in the scintillator. Note: Alternatively the preamplifier can be disconnected to connect the Signal output directly to the oscilloscope (50 Ω DC). This is an option in case timing is not measured. For simultaneous measurements of timing and energy, the Amplified Signal is used for timing and the Monitor output for the energy measurement. Note: Even though the preamplifier may be in saturation, timing can still be measured at the steep rising edge of the Amplified Signal close to the baseline. Usually the monitor output is used to measure the charge released by the corresponding to the deposited energy in the scintillator. Evaluation Kits can be ordered either with unmounted or premounted LYSO crystals on the s: For PM11 (1.2 x 1.2 mm² active area) LYSO with 1.2 x 1.2 x 4.0 mm³ For PM33 (3.0 x 3.0 mm² active area) LYSO with 3.0 x 3.0 x 5.0 mm³ For PM66 (6.0 x 6.0 mm² active area) LYSO with 5.0 x 5.0 x 5.0 mm³ 4.1 Energy Spectrum In analogy to section 3.1, at the oscilloscope the trigger has to be set to the signal above the baseline and the pulse area as a measure for the energy is histogrammed. Figure 3 shows an example energy spectrum of a ²²Na source measured with the Monitor output. The used scintillator is LYSO with 3 x 3 x 5 mm³. Fig. 3 Example of an Energy Spectrum Measured with PM3350 at 4 V overvoltage, ²²Na source and LYSO 3.0 x 3.0 x 5.0 mm³ 350 300 Counts [a.u.] 250 200 150 Energy Resolution 11.9% FWHM at 511 kev (corrected for saturation) 100 50 0 0 250 500 750 1000 1250 Energy [kev] 08/2016 Rev. 1.0 Page 5
4.2 Coincidence Time Resolution Two Evaluation Kits are mounted facing each other Note: Two M6 mounting bolts are supplied for alignment when ordering two Evaluation Kits, they are screwed to one of the Evaluation Kits, the second Evaluation Kit is slid on the mounting bolts This example uses two PM3350, each equipped with 3.0 x 3.0 x 5.0 mm³ LYSO with a ²²Na source placed exactly in between the s Note: ²²Na has two decay branches. It emits two 511 kev annihilation γ rays in opposing directions, originating from a β+ decay. The second decay emits a single 1.27 MeV γ ray. Of interest here are the two 511 kev γ rays for the coincidence measurement. Monitor outputs are connected to a coincidence logic, e.g. realized by the oscilloscope Lower threshold of the coincidence logic defines the lower energy cut-off. The thresholds for both Monitor outputs are set to the minimum between Compton edge and 511 kev photopeak to filter for the energy respectively coincident events. The Coincidence Timing can then be measured by the time difference of both Amplified Signals. The output of the coincidence logic triggers the measurement of the timestamps of both Amplified Signals. Note: Best timinig is achieved with a timing measurement close to the baseline. Typically with LYSO the optimum is around 2-3 pe. The time stamps of both Amplified Signals can be measured e.g. with a leading edge discriminator, a constant fraction discriminator or using an oscilloscope. The time difference between both time stamps is then histogrammed as shown in figure 4. The Coincidence Time Resolution is the FWHM of the Gaussian distribution. Fig. 4 Example of a CTR Histogram Measured with two PM3350 at 4 V overvoltage, ²²Na source and LYSO 3.0 x 3.0 x 5.0 mm³ 2500 Counts [a.u.] 2000 1500 1000 CTR 180 ps FWHM 500 0-1 -0.5 0 0.5 1 Time Difference [ns] Evaluation Kit Quick Start Guide
5 Appendix 5.1 Variant for Optical Bench Mount The Evaluation Kit as also available in a different form factor for optical bench mount including the preamplifier (cf. fig. 5). The PCB with the is premounted to a Thorlabs CP02/M Frame (SM1-Threaded 30 mm Cage Plate, 0.35 Thick, 2 Retaining Rings, M4 Tap). The is centered on the optical axis. The cables are MCX to SMA and are supplied together with the Evaluation Kit. 5.2 Bias Source As an addon to both Evaluation Kits, a Bias Source is available (cf. fig. 5). It offers an adjustable bias voltage from 20 to 40 V with either positive or negative polarity. Current limit can be set to either 2 or 20 ma. For full technical specifications please refer to the KETEK Bias Source Datasheet. Fig. 5 Evaluation Kit for Optical Bench Mount with Bias Source Bias Source premounted in optomechanic frame Preamplifier 08/2016 Rev. 1.0 Page 7