Jarom Jackson and Dr. Dallin Durfee, Department of Physics and Astronomy
Purpose of the Project
The experiment which we are building here in Dr. Durfee’s lab is a novel one, the key part of which is an ion interferometer. The interferometer consists of a beam of Sr+ ions which will be split in half. The two halves of the beam will travel along different paths, and then be recombined. Depending on the difference of phase of the two beams on recombining they may either constructively or destructively interfere with each other. Since the phase change of each beam depends on the potential energy along the path that beam follows, this will allow us to very finely measure the difference in potential energy along two paths. In other words, the interferometer takes advantage of the wave nature of matter to allow us to perform very precise measurements of an electric field.
An ion interferometer of this type has never been built before, and it will allow us to perform many interesting experiments and measurements, such as the ultra precise testing of some basic laws of physics. One potential application will be to establish a lower limit on the rest mass of a photon (if it exists).
The purpose of this project was to develop and implement an oscillating circuit with a modulated frequency for use in a laser locking apparatus. This apparatus was to then be used as a step in building the ion interferometer.
Results
All aspects of this project were completed, though with some delay compared to the timetable given in the original proposal. The first step was to schematically design the modulating oscillator and create a Printed Circuit Board (PCB) layout. This layout was then used to create the actual PCB boards onto which I assembled and tested the circuit. Initially there were some serious difficulties, especially with electronic noise which had a negative impact on the quality of the signal. I was able to find ways to deal with this and make the circuit meet design expectations.
The next step was to integrate the oscillator with other electronic components (detailed in the original proposal) to create a setup for frequency locking of a laser (see figures 1 and 2). The frequency of a laser used in atomic physics experiments must be very carefully tuned and held at an exact value with very little tolerance for drift and jitter that normally occurs. The purpose of this setup was to provide a feedback loop through which the laser could be stabilized for use in our experiment. This is commonly referred to as frequency “locking.”
The setup, including the electronics and an optical setup which I put together have since been put to use in locking a 461nm (blue) laser. The fluorescence caused by this laser can be seen in the
vapor cell in the locking setup whenever the laser is stabilized and on resonance (see Figure 3).We are now using this laser to trap and cool the Sr atoms which we will use to create the ion beam that is the key part of the ion interferometer. In addition to this, the other half of the system I built will be used for another laser which will be used to probe the Sr+ ions.
Commercial alternatives for the electronics that I designed and built for application in our lab cost between $3,000 and $6,000 each (totaling for us $6,000-$12,000). The parts for the dual system I built total about $2,500, so even factoring in the cost of the labor put into designing and building this, we saved a substantial amount. In addition, because the electronics were designed and build here, they are much more easily adapted to suit our needs.
The experience that I gained from this project has already proved valuable in work that I have since done, both here at BYU and during an internship with Sandia National Laboratories. Because of my experience here, I understood much better the workings of, and limitations of similar commercial devices that I worked with there, and was able to accomplish a lot. Most of what I did there was in building laser systems, where I got to use expensive commercial equipment that does essentially the same things as the electronics that I designed for our lab here at BYU.
