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[[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_s = 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_s = 5 V]]

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.  

A wooden dark box was initially constructed for the a hybrid photo-diode (HPD) module DEP PP0350.  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.  

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!

Running this setup with an HPD 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 - they were self-calibrating!