Marshall van Zijll and Dr. Dallin Durfee, Physics
Our research group has spent lots of effort and time building an ultra-stable laser current controller. This stability is essential for our application of atom interferometry so that our measurements could be very precise. The overall development of our controller has taken almost a year longer than expected, but regarding the results we have obtained it was time well spent. The specific part of the controller I focused on was the microprocessor and it’s relation to the DAC (digital to analog converter), so I will explain the processes I went through.
Initially, I had to program the microcontroller bootloader, and this was difficult because we didn’t want to waste $100 on purchasing a programmer that we would only use once. By studying older models of microcontrollers, and searching for methods used to program the bootloader on those, I was able to adapt previous methods to work for my purpose.
After successfully uploading the bootloader, I studied the needs of our project, and came up with an outline for a program that would run the DAC, receive input, and display all pertinent information on an LCD display. I’ve continually made updates to the code that runs on the microprocessor, and it is still being improved even though it is plenty sufficient for our needs.
We found that the use of a DAC along with a microprocessor has greatly reduced the noise in our circuit. This is because the potentiometer that was previously used requires long cables to allow a user to change the value. The capacitance and inductance in these long lines added much unneeded noise. The use of a microcontroller eliminates this extra noise since the signal is passed digitally to the DAC. The DAC is then placed right next to the laser, and no cables are even needed to carry the analog signal.
Another great advantage is the repeatability offered through use of a microcontroller. It is very simpole to work on an experiment, then turn of the microcontroller to make adjustments to the laser, and then return directly to the value used earlier. With a manual potentiometer, this is very difficult. The DAC also offers more than 36,000 values to use, much more than the couple hundred from a manual pot. This allows precision that was unattainable previously.
We are finalizing our designs and we have already sent in a paper to be published on the work we have done. We are also extending our ideas to be used in a PID controller, because with the use of a microprocessor we can find ways to automatically scan, and lock a laser without time consuming effort.
I am very grateful for the grant we received, and I know that the work would have been impossible with funds to keep us progressing. Thank you very much for your support of our project.