Testing the new APD heat sink.
Author: Kate Wolchok | Major: Physics and Music | Semester: Spring 2023
Hello, my name is Kate Wolchok and I am a Physics major here at the University of Arkansas. After taking modern physics with Dr. Hiro Nakamura in the spring semester of 2022, I decided that I would like to enrich my education and participate in undergraduate research at the University. I have now been conducting research in photon correlation for a little over a year, with my main project this semester being to build an avalanche photodiode single photon detector.
An avalanche photodiode single photon detector, or APD, uses a semiconductive photodiode that converts incoming photons into an easily readable electrical signal. APDs are available to purchase, however they are very pricey, costing upwards of $6,000. For this reason, I have decided to build my own detector, making it easier to obtain an arsenal of APDs. Having multiple detectors opens numerous interesting experiments in path identity and quantum coherence using multi-photon systems.
Through a research grant awarded to Dr. Nakamura, our lab has also been able to purchase one commercial APD. This summer I plan on comparing my detector to the commercial one through measurements of dark count, quantum efficiency, and dead time. I will be able to see how my detector stacks up against the commercial one with this data, and plan to optimize my design to make a detector just as efficient.
A reoccurring problem when building the APD has been getting the diode down to an optimal temperature, as the device works best when operating at anywhere from -20℃ to -30℃. To cool the device, a dual stage peltier element is used in conjunction with a thermoelectric cooler that allows us to control the temperature. A peltier element uses a current to make one side cold, and the other side hot. Building a near airtight cavity with an efficient heat sink to dissipate the heat on the other side of the peltier element is needed so there are no convection currents around the diode, and the heat from the one side does not affect the other. After 3D printing a case for the heat sink and fan, seen in the photo above, the cool side was able to get down to -22℃ without any insulation on the top! I am confident that even lower temperatures will be easily obtainable when the device is put into the near airtight chamber.
Now that I have the detectors, I have begun the shift towards taking photon correlation data using the knowledge from Heisenberg’s energy-time uncertainty principle. This uncertainty principle essentially means the more we know about energy, the more uncertain we can be about the time, and vice versa. This principle works in my favor for photon correlation measurements. Focusing light from one of our labs lasers onto certain substrates emits photons with sharp energy peaks, giving way to more time uncertainty, or a longer coherence time, which is easier to detect. Currently I have been taking photo luminosity measurements of different substrates to determine which ones have sharper intensity peaks, and can be used to get the correlation data. As of now, it seems that sapphire (𝐴𝑙2𝑂3) will be the best candidate.
This semester, I’ve acquired so many new skills through building the APD like learning to solder, using new software, and getting increasingly more comfortable when working with electronics. I’m so thankful I’ve been able to continue doing research through this Honors College Research Grant and I’m very excited for this summer and the semesters ahead, where I plan to continue my research in quantum optics here at the University of Arkansas.