Oberlin Blogs

Ah, you'd like two tickets to the laser show?

January 11, 2012

Sophia Chen ’12

This Winter Term, I'm working on a research project in atomic physics, where I use femtosecond frequency comb spectroscopy to learn more the atomic structure of potassium. I've been working with Jason Stalnaker, a professor here, who has been incredibly helpful and patient and knowledgeable and all the adjectives that are necessary for me to have a productive and enjoyable honors project.

Quick (and incomplete, sorry) explanation on what my project actually is:

femtosecond frequency comb = a laser that emits pulses of light instead of a continuous beam. The pulses are ~0.000000000000001 seconds long. (Sorry, I typed all those zeros to be obnoxious.) As a result of the Heisenberg uncertainty principle, which says that the shorter the pulse, the less certainty in frequency, instead of being a monochromatic laser, the comb spans a whole bunch of colors that are evenly spaced in frequency space. Once we stabilize the laser, the colors are so evenly spaced that we can use the laser as a sort of "frequency ruler" to measure frequencies of light to very high precision. Our goal is to measure the frequencies of light that excite potassium.

A green glow surrounds a red light. — It's unclear what this picture is. No, it is not Jell-O. The fainter red light is coming from the crystal that produces the frequency comb. The green light is used to pump the crystal so that it lases, and the fainter red light is the actual frequency comb.

Lab equipment and wires glow green. — The red light from the crystal is then sent through this cool optic fiber that broadens the spectrum of the light so that it becomes super colorful. It has proved both useful and pretty. Unfortunately, my iPod camera is not very sensitive and kind of sucks, so you can't see all the colors.

spectroscopy = characterizing matter by studying its spectra, i.e. the frequencies of light that it emits.

Why potassium? Potassium is an alkali metal, which means that it has only one valence electron. This means that it is relatively easy to model theoretically--ignoring the inner electrons, it is similar to hydrogen, the simplest atom. Thus, we can compare our experimental measurements to theoretical calculations for potassium.

Plus, this pulsed laser technique for spectroscopy is new and pretty cool in general, and it's been a highly informative and interesting lesson in atomic physics for me.

A taped-up cardboard box with wires attached — The potassium is housed in a small glass cell within this mostly light-proof cardboard box. The light detector is also inside this box, which blocks out the ambient light so we can actually see the light from the potassium. Together with my lab partner Mike, I made this very beautiful, hi-tech setup. Please appreciate the skilled masking tape job.

I've been working on this project since last spring semester, but this Winter Term is the first time that I've been able to dedicate the continuous chunk of time to this project that it deserves. While research during the semester gives you a nice taste of what science research entails, it's hard to actually be very productive because you can only work in 2-3 hour chunks twice a week. Our laser takes a couple hours before it settles down enough for us to take real measurements, so I've really been enjoying having the whole day to work on the project.