Jie's Experimental Method
A darkened enclosed box was built to house the SiPM. Since electromagnetic radiation(in the form of heat) can fire the SiPM very efficiently , the box had to eliminate as much ambient light as possible. It consisted of a 3' x 1' x 1' box, made of wood that was painted black. On one end of the box, there was an LED and pulser circuit for the purpose of calibrating the SiPM. On the other end, the SiPM was mounted on a metal arm with heat conductive material to make sure that the temperature of the arm matched the temperature of the SiPM. Attached to the metal arm was a temperature controller. The temperature controller consisted of a heat sink that was receiving constant feedback from a thermometer on the metal arm. If the temperature was too low, then the thermometer would send a signal back to the heat sink. This signal would cause the heat sink to heat up, causing the arm as well as the SiPM to get warmer. The signal from the SiPM was amplified by an amplifier that was mounted right next to the SiPM on the arm which was then connected to an oscilloscope which could display the results of the experiment.
There was a large amount of electromagnetic interference in the wires. This was due to the many power wires that crisscrossed the device. The interference was especially troubling in the wire between the SiPM and the amplifier. Any slight interference would be magnified by the amplifier with the actual signal, causing the signal to be extremely muffled. To combat this, grounded shielding was placed in the wires inbetween the SiPM and the amplifier and many other electrical wires, such as the power supply wires were also grounded.
Calibration
During data collection, the Oscilloscope was connoted to a server with data collection software. The rate at which the data was collected was one waveform per second. Before data collected could begin, the device needed to be calibrated and the energy of one amplified event from the SiPM needed to be determined.
First the LED that was installed in the other end of the box was partially covered by a filter and connected to a pulser circult. This resulted in the LED sending clear pulses of a few photons racing towards the SiPM every couple of miliseconds. The data was taken for over 50,000 events and the data was put into a histogram. (see picture below).
The peaks of the data are clearly visible. The SiPM functions as an array of avalanche photodiodes that store and release energy. Each pixel on the SiPM releases a certain amount of energy when triggered. The peaks clearly indicate the number of pixels that were triggered with each pulse. The first peak on the histogram would represent a pulse in which no photons were detected, followed by 1 then two then so on.
The difference of energy in-between the peaks was determined mathematically. Since photons are a very reliable way to obtain peaks, this gives us a clear picture of how much energy would be released if the SiPM was to detect one event. It allows for easier analysis of the data
Collection
The SiPM was set to the correct temperature and allowed to achieve the desired temperature. Then the test was set to run a minimum of 14 hours. This allowed the data collection software to collect over 50,000 events worth of data. 50,000 events is a statistically significant number that minimizes the error associated with random electrical and electromagnetic noise.
The data was recorded in a server for further analysis.