Bonnie J. McLaughlin and Dr. Scott Bergeson, Physics and Astronomy
High power green lasers are used extensively in laboratories for numerous applications. The cost for commercial green lasers is around $60,000. When I was searching for a research project for my senior thesis for my BS in Physics, Dr. Bergeson proposed I build a green laser for use in the experiments of the Atomic Molecular and Optical (AMO) research group. The laser was designed to pump other lasers with specific wavelengths for studying calcium at extremely low temperatures. We had also hoped to form a kit for building such lasers.
At the time of the ORCA proposal, the most power I had achieved with my laser was 2.1 W. Our goal was 5 W. The 2.1 W was seen in August 2002. During fall semester, our lab was being remodeled and we moved the green laser to another building. Upon returning to our lab in January, the laser did not work as well as before. We suspected that the heat sink for part of our laser was insufficient and the proposal was for us to build a new heat sink and temperature controller. In January and February we installed the new temperature controller and heat sink. Results showed that there was no improvement.
Also during the semester, Î wrote my thesis and presented at the Spring Research Conference in March 2003. The timing of the scholarship was serendipitous because the our funding had run low and I would not have been able to continue the project without finacial support. I was equally benefited by extra funding from the department which allowed me to continue doing research 20 hours/week for spring and summer terms.
In May, we were able to collect data regarding the stability of the laser. It was very stable and remained very close to the 532 nm wavelength. With this data, I was able to present the research at a poster session of the Division of Atomic Molecular and Optical Physics (DAMOP) conference in Boulder, Colorado in May 2003 along with the graduate student who had helped me build many of the parts for the laser the summer before.
Presenting at the conference helped me find a new drive for completing my laser. I saw the labs at the university that used one and talked to many people who used such lasers. Before the conference, I wanted to finish the laser because it was my project and I had worked so much on it. After the conference, I wanted to finish it to be able to help people like those I met and to get it working for our research group to be able to have a laser like the ones others have. Spring and summer terms were a busy time in our laboratory. We had several REU students and two physics teachers working on projects in addition to the grad students and the rest of us undergrads. I began to take data to see if we could separate our laser cavity into two parts to improve its performance, as Dr. Bergeson suggested. I shared the data with Dr. Durfee, the other professor who works in the AMO lab. He felt the power was insufficient for the double cavity to work.
The rest of my time was spent with two major attempts to improve the laser while at the same time troubleshooting problems that arose with the temperature controller and the driver for our pump laser. The first attempt was replaces two achromatic lenses with singlets. We thought the high power of the pump laser that passed through the lenses might have damaged the lenses. The second attempt was to replace our gain crystal where the lasing occurs with a shorter crystal to minimize the effects of thermal lensing where the heat gradient experienced by the crystal cause it to create a lens effect, distorting our beam. After these attempts, I tried to manually adjust the mirrors and lenses to optimize our power. The best power achieved at this point was 1 W. Sometimes experimental physics consists of finding broken parts and waiting for the replacements.
I admit that I made mistakes in not communicating my initial results at the beginning of the summer with Dr. Bergeson. Perhaps the double cavity would have worked. I also made a mistake which resulted in spraying all the mirrors and lenses on one of our optics tables with cooling liquid. Everyone had to stop what they were doing to help clean the optics and we went through several packages of expensive lens tissue. I felt awful.
Dr. Bergeson was quite busy with helping everyone and working in his office. I felt I should try to do my best on my own and not impose too much on the work of everyone else. It was I who pushed to keep the project moving when the professors were considering placing it on a back burner.
At the end of the summer, I had an idea as to why the laser had such poor performance. It had to do with the way the laser beam traveled through our second laser crystal. I felt that if it could travel more directly through the center of the crystal, the performance might be improved. To achieve this, I removed the crystal mount and asked our machinist to file a small part of it to prevent the mount from clipping the path of the laser. During the process, unfortunately the heater for the mount was damaged in the process.
As fall semester began, I proposed that we order and install a new inexpensive heater. However, Dr. Bergeson did not want to continue at the time what appeared to be a fruitless struggle. He allowed me to give him the part number to replace it, possibly next year. Perhaps there would be no effect from moving the path of the beam.
It was hard to give up my struggle. But I am grateful for what I learned from Dr. Bergeson, Dr. Durfee and the grad students I worked with. I gained a lot of experience, presented at the Spring Research Conference and at DAMOP, and wrote my senior thesis. Thus I was able to do a lot with the project even though it did not turn out how we had hoped. It was a good project and relatively simple in theory. However, we gained some appreciation for why high prices are demanded for such lasers.
During the past year, I decided I would like to teach high school. I am looking forward to doing my student teaching next semester.