1 SiPM studies: Highlighting current equipment and immediate plans Lee BLM Quasar working group

2 Tests to be performed 1)Preliminarily checks on SiPM performance Dark count rate (DCR)-Check SiPM is performing as expected from vendors expected DCR Gain from voltage breakdown (Vbr) to max Vbr+3V 2)Saturation studies Measure saturation curves of SiPM as a function of incoming photons Requires understanding of incoming photon number (most difficult part) 3)Timing studies Measure output over time for a high intensity light source over various pulse lengths

3 Equipment MPPCs 1)Hamamatsu S C pixels + readout electronics 2)Hamamatsu S C 3600 pixels + readout electronics 3)ST-M prototype used by previous quasar member. Very low pixel number. Probably not used. Sergey is asking around to acquire some samples from vendors Scopes 1)Lecroy waverunner 1GHz bandwidth– No Histograming function 2)Yokogawa DL9505L 500 MHz bandwidth – Histograming function but a little backward in operation Voltage supplies: Low voltage supplies to power amplifiers. High voltage supply <100 V to bias SiPM. Supply unit also acts as current reader. Should be possible to measure ~nA. Needs investigating Light sources: Diode laser 635nm (red) 5mW. Borrowed from another group member, We can replace laser for other wavelengths Light modulation: Basic 10MHz pulse generator, rise time ~ 10 ns with minimum pulse length ~40 ns – Not the best but will do for now Equipment is clearly basic at the moment. The plan is to build up experiments and when we reach a limitation aim to borrow adequate equipment.

4 Measuring Gain 3) Measure IV curve : Current rises once breakdown voltage has been reached gain can clearly be seen Three proposed methods to measure/observe gain in SiPM Measured current includes afterpulsing/crosstalk so not completely accurate. 1)Integrate voltage over time pulse of SER. Build histogram of integrals and take the mean Calculate Gain from histogram mean. Increase overvoltage and plot Gain vs V Br Method 1 and 2 are longer than method 3, which is affected by afterpulsing and crosstalk. Method 2 is the easier of the two so this will be used 2)Calculate gain using the amplitude difference between two consecutive peaks Both methods will produce a graph such as:

5 Saturation Studies. Dynamic range of SiPM limited by pixel number. For the ‘ideal’ saturation curve (graph), the signal from the SiPM should increase linearly for a low number of detected photons until saturation occurs. The curve follows the form (not including afterpulsing and crosstalk): With maximum output : Saturation = incoming photons produces the same output. Problem for BLM purposes, when non-linear the resolution on the number of incoming photons worsens. The experiment will be performed in two stages: 1) using the laser observe saturation at a high intensity and minimum pulse length 2) calibration of SiPM with unitary gain (i.e below Vbr) to measure the number of photons on the SiPM. → Hard as the output will be low (~pA). Another possibility would be to buy another detector (APD or pin?) and beam splitter (or light power meter)? We will require to understand crosstalk and afterpulsing effects so they can be accounted for in data. Once this has been achieved we would like to see: Overvoltage dependence on saturation Pulse length dependence on orders of magnitude expected from output of fiber (timing studies)

6 Saturation Studies. +12 V -12 V HV Scope LTB SIPMSIPM AMP A Amplifier power source APD / power meter Splitter Solution if SiPM in no gain mode fails to work LD Current controller Pulse generator 10 MHz Tpulse ~ 40ns Control power Λ=635nm Experimental layout of equipment Laser output will be fired directing at sipm Ambient lighting will be turned off and if possible the experiment will be enclosed Iseg, HV supply and current meter

7 Timing Studies. Consider the case where Nphotons > Npix and Tpulse > Trec such an output is shown in the plots. Output can be seen and explained in terms of three regions 1) Peak – Initial avalanche. All pixels fired with a high intensity light source. Maximum output is reached. 2) Plateau – Retriggering of pixels during recovery and after recovery so pixels are not triggering at the same time produces a plateau. 3) Fall – Light source turned off, final recovering. After pulsing produces small output in some cells but output falls to zero after a long enough time. 4 us pulse50 ns pulse Method of measurement still being discussed. Methodology to be finalized on

8 Summary Several experiments will be performed with the SIiPMs Checks on performance compared to vendor specifications Saturation studies Timing studies at high intensities A methodology has been developed for the first two experiments Timing study methodology still being discussed Saturation studies are critically dependent on the ability to measure the number of incoming photons New equipment may be required (borrow?) to solve this We do have a power meter available for all visible wavelengths, not clear if this will be sufficient. Equipment is simple at the moment but the idea is to borrow light sources etc once we ‘outgrow’ our current set up.