Author: Jackson Marsh | Major: Mechanical Engineering

My name is Jackson Marsh, and this semester, Spring 2022, I started researching in the Nano Energy and Data-Driven Discovery laboratory with Dr. Han Hu of the Mechanical Engineering department. Thanks to Dr. Hu, I was able to partner up with Stephen Pierson, Matthew Buchanan, Timothy Loftness, and Landon Lemmons as we began to research Solar Pumped Laser 3D Printing. My focus as a part of this team was on the concentration of light using Fresnel lenses. Concentrated light can be directed into a tube to create a laser for 3D printing in space, allowing for additive manufacturing in difficult environments. The ability to manufacture things in space is extremely important as humans look to stay in space longer and live on other planets. As infrastructure is created in space and on other planets, the only sure power source available will be the sun, which makes solar pumped lasers a great solution. This work excites me because I plan to go to graduate school to pursue a Master’s in Aerospace Engineering. I one day hope to help make living on Mars a reachable reality. I believe that this research is a great example of one of the many innovations that will have to be made to make living on Mars a reachable reality.

The first thing I had to do was learn what a Fresnel lens did and if multiple lenses together resulted in better brightness or larger focal points. I expected this to be a simple task, but it ended up being more complex than I thought. Fresnel lenses were created to be extremely light so that they could be made very large but still be movable. They are also special because they are flat on one side and bumpy on the other. The “bumpy” side is actually where the glass has been cut to create tons of tiny convex lenses. Because of this, if you shine a light through the convex side, the light focuses all of the light at the focal point. However, if you shine the light through the flat side, the light mostly collineates, meaning the light rays run parallel to each other. This means that the focal point is much dimmer and the area surrounding the focal point is of equal brightness. This difference in sides provides an experimental purpose and a practical purpose. First, to simulate the light from the sun best, our light needed to be collineated. Therefore, we were able to pass all of our light through a Fresnel lens’ smooth side and collineate our light. Then because the lenses have been cut and have less mass, they are perfect for space flight where you need to minimize as much mass as possible.

I then started using the lenses to focus on a blank backdrop. I had three lenses to work with, a two-inch diameter (small), a four-inch diameter (big), and then a lens that was rectangular and the size of a sheet of paper (sheet lens). I used the sheet lens to collineate the light, and then I would set up the small and big lens at the other end of an optical table. The light would then pass through the lens, and I would record what I saw. I arranged the small and big lenses alone, light passing through one side first then the other. I then took the two lenses and spaced them out to try different collineation and focusing patterns. For example, I focused the big lens onto the small lens at the big lens’ focal point. I noticed that the focal point of the small lens moved and was slightly dimmer than if I had just used the small lens. Qualitative observations like this led me to make three hypotheses: 1) Collineation makes the light better to focus; 2) The smaller the lens the better the light would be; and 3) The more lenses you used the worse your focal point became. I use better and worse in describing the brightness and power that is produced. The goal of this was to create the highest power output possible. However, before buying any measurement tools I had to come up with these hypotheses to know what to buy. That is why I did the qualitative experiments first. When my first instrument came in, I ran into a problem: it didn’t work. I ended up having to send it back; however, I took this opportunity to make sure that I was getting what I needed. I ended up switching brands and got a device called a pyranometer. It measures irradiance, which is proportional to power, and can be used to find power. With this, during the last week before finals, I was able to test my hypotheses. I found that my first hypothesis was correct. When I collineated the light before focusing it, the irradiance went up. My second hypothesis was wrong. The smaller lens provided a much lower irradiance than the bigger lens. My final hypothesis was correct. The results of passing light through two lenses was much worse than passing it through either lens individually.

These results were very nice to receive at the end of the semester. Being able to see actual data after theorizing for so long was very rewarding. I could not have done this without the guidance from Dr. Hu who helped me obtain the necessary equipment and helped me formulate some of my first questions to answer. I worked closely with Mathew Buchanan who helped me with the theory before we started the qualitative and quantitative setup. He will also be helping next semester as we work towards taking what we know now about concentrated light and turning it into a solar pumped laser. We still need to know how this concentrated light affects temperature and what the true power numbers are, but this semester proved to be a promising start.