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→Bench Test Setup
== Bench Test Setup ==
== Bench Test Setup ==
A wooden dark box was initially constructed for the a hybrid photo-diode (HPD) module. A pulser was installed on the opposite end of the box composed of a fast LED driven by a pulser circuit shown on the right.
[[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]]
Running this setup with an HPD of 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 - they were self-calibrating!
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 installed into the wall of the dark box via a custom-designed light-tight frame.
[[Image:DarkboxDiagram_HPD.png|frame|Diagram of the dark box with the HPD module installed. V<sub>HV</sub> = -12 kV, V<sub>b</sub> = 60 V.]]
[[Image:DarkboxDiagram_SiPM.png|frame|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)]]
== SiPM Measurements ==
== SiPM Measurements ==