March 29, 2004
March 29, 2004. After a long break due to Spring Semester classes, I'm finally updating my journal. Lots of things are going on. I have a job this summer at JILA at the University of Colorado, Boulder in the Murnane Group sponsored by the NSF Research Experience for Undergraduates. I'm really excited about going there, I hear Boulder is amazing, and JILA does some of the best optics research in the world.
I will be participating in Stony Brook's celebration of undergraduate research. I have submitted an abstract and will be displaying a poster on April 21. I'm working very hard on it, guaranteed it will be the best looking poster in the whole exhibition. It is also going to be displayed at the atomic, molecular, and optical physics conference (DAMOP) in Arizona at the end of May.
We installed a new vacuum system on the bichro experiment. The new piece has four large windows instead of two small ones, so bichromatic beam collimation can be done from two dimensions. Replacing a huge piece of the vaccuum system is no easy task. Each window has to be secured on by about 30 bolts and strategically tightened to form a vacuum seal. The modules are pretty cool looking, they look like they should go under water. It took four people to get the piece into place and to tighten all the screws. Naturally, not everything goes smoothely, so seven hours later, at three in the morning, it was finally done we could all go home.
The Rydberg experiment is also going multi-dimensional. Jose and I (more Jose than I) designed a two dimensional laser cooling apparatus. It is an assembly to mount mirrors specially coated for the light frequency we are using. It looks like a shallow can-like ring, with pieces cut out from the inside to hold the mirrors so the light reflects exactly in the middle. It came back from the machine shop today and it's really cool to see it in person. I didn't think it would ever be real.
Optical physicists who spend most of their time in dark labs are interesting creatures. Their eyes grow considerably larger and their skin paler, and they begin to refer to small ring-like objects as "my precious." Fortunately, a little bright light keeps them under control.
January 21, 2004
January 21, 2004. I learned how to turn the diode laser on and off. It's not as simple as turning on and off your TV. If you forget to turn down the power before you shut it off, you can blow out the diode and these things ain't cheap. I also learned how to properly clean optics. I also realized that I forgot to take into account the absorption of the prism glass. Jorg and Matt installled the new fiber amplifiers today on the bichro experiment. It can get kind of frustrating working for hours and hours at something at not feeling like you accomplished much. I can always say, though, that I learned from it.
I was finally able to test the prisms today. I used the infrared light. It turns out, there is not much difference in the amount of absorption and the index of refraction with red light. In fact, the absorption should be less for this type of glass. This experiment proved difficult since the fiber optic cable I used to transport the beam changed polarizations every time it was moved. It was also difficult to tell the exact polarization of the beam. I used a polarizer to make sure the light was polarized in the right direction so there would be no reflection when the prism was at Brewster's angle. I changed the polarization until the reflection was no longer visible. However, even when I did that, I still not get the amount of light out of the prisms that I expected to. I don't know what else to do with them. I don't know what is causing the extra loss of power. If there is not enough power transmitted for laser cooling, we will have to get the surfaces anti-reflection coated.
January 20, 2004
January 20, 2004. Today I discussed possibilities for a project to do during the semester. I could continue work on the Rydberg experiment. There are still many things that can be done with it, such as building a container for the frequency doubling crystal, building the mirror assembly for two dimensional laser cooling, or possibly analysis of the data collected during the experiment. Matt Eardley will begin his own experiment soon to atempt etching using the laser cooling from interference patterns of laser beams. That project will involve many different disciplines, including chemistry. I could assist him in beginning his project. Or I could attempt a project that is totally different, on my own, in the Laser Teaching Center, such as optical tweezers, or any number of things that people from past years have worked on here. I will also need to continue my work with the beam expander, I expect to be able to present something on it at the undergraduate research conference in April.
I have done more work with the beam expander. Today, Jorg assisted me in finding the profile of the beam using a CCD camera. I was afraid to try it myself, the CCD chip is very sensitive, and if overloaded with power, will be permanently damaged. First we tested the filters on the camera to find out how much light they block out. That inolved using a power meter. When we finally saw the beam on the computer screen, we discovered it was not circular, but elliptical, with its major axis diagonal, which would be further distorted when the beam expander was used. We changed the fiber coupler, to a better shape, but the beam is too big. When I tried to test it with the prisms, the shape was not what I expected. The size seemed to be too big for the prisms. The setup will be very difficult to test with the wavelength I am using now, which is 795 nanometers, which is twice the frequency I built it for (389 nm). Wavelength affects index of refraction, and the reflection and absorption of the beam will be quite different infrared rather than ultraviolet wavelength. We will need to find a way to test the setup with the blue beam.
January 15, 2004
January 15, 2004. Oleg and Olexij would not let me adjust the prisms since they had already aligned the setup. They decided to run the experiment as is, so we'll see how it turns out. The beam that's coming out of the prisms is not elliptical, which might be a problem. The problem, however, is not from the prisms, but from the beam splitter, which is actually just an ordinary microscope slide. Because there are two surfaces the beam is reflecting off of, you don't get an elliptical beam. I suggested it might be better to use an anti-reflection coated beam-splitting cube, which has only a single reflecting surface and might eliminate the problem. I tried using the CCD profiler to see what the beam looks like, but it was behaving very strangely; it might be broken. This wouldn't be the first time that thing has caused problems.
Eventually, the Rydberg experiment will need laser cooling in two dimensions instead of just one. However, the vacuum chamber only has windows in one dimension, so a solid apparatus will need to be built out of aluminum or steel to hold the mirrors. It will need to be designed by the group and built in the machine shop. There is a problem with it, though. The current setup does not allow any space for it, so the entire setup will need to be reworked, and of course, it can't be done quickly and easily. I drew in my notebook the idea of what this thing would like in perspective. I honestly didn't expect to need my drawing skills when I majored in physics.
January 14, 2004
January 14, 2004. I found the problem with my formula. The one that actually works is whole lot simpler than the one I thought of originally. It is also much more intuitive. Usually students need to derive formulas that are already given, in this case, but it is much more difficult to come up with a formula for something that you don't already have. There are a million ways to get from point a to point b, but there is only one simple way, and that's a straight line. I spent a lot of time trying to prove a formula that was wrong, but the fact that it took so much time should have clued me in.
It turns out, in order to achieve the desired magnification for the beam, each prism needs to be rotated 7 degrees. I redrew the pattern, but this time I did it using a Linux program called Xfig. It took about an hour and a half, but I figured out how the program works and now I have a very nice looking pattern.
Looking at physics problems in a real life setting is much different than in a textbook. I feel like I have a better understanding of what a formula means. It's a lot more than plugging in numbers. I think experience will be very valuable in the long term and I think it will give me a little jump on next semester.
January 13, 2004
January 13, 2004. Today I derived a formula to calculate the amount of expansion of the laser beam by a single prism, which is dependent on the angle of incidence. I used this formula in excel to make a graph of magnification as a function angle of incidence. However, there must be an error in the formula. At the Brewster angle (the angle at which the angle of incidence and the angle of transmission add up to 90 degrees), the magnification of the beam should be the index of refraction, which it is not. The answer is would be acceptable if it were experimental data, however, without experimental error, the results should be ideal. I tried checking my formula theoretically, but it's difficult becuase of all the trig functions. I'll have to just start fresh and re-derive the formula.
January 12, 2004
January 12, 2004. Since the prisms did not arrive Friday morning, in the meantime, Dr. Metcalf gave me the assignment of calculating the force of a light field on moving atoms based on their velocities. I didn't really understand how to do this, but he gave me a formula and Claire helped me write an Excel formula in order to graph it. Today I was able to maximize the amount of force on the atoms and make the range large enough so it could trap atoms at every velocity. I did this by adjusting the amount of intensity and the detuning of laser beam on the spreadsheet. My values seemed to be correct, I just need to determine the size of the beam so we can know what power to use.
The prisms arrived on Friday afternoon, but I had no time to mount them. I finally mounted them today. It didn't take very long because I had everything already set up. However, the beam expansion that I calculated will probably not be enough, which gives me a new assignment. Having the beam be incident on each prism at the Brewster angle, reduces beam expansion in addition to eliminating reflection. That means I will have find a way to maximize beam expansion, while minimizing loss of intensity of the beam. Fortunately, the reflection is still close to zero when you turn the angle away from the Brewster angle. However, the question is how far can you turn it before there is too much loss and how much loss will there be. Dr. Metcalf and I derived a formula to determine this. There is still a lot more that needs to be done with it. I need to find out more about the Brewster angle, review Taylor Expansions and trig identities, and then plug numbers into formula and see what I get. It should keep me busy enough for the next two weeks.
January 8, 2004
January 8, 2004. The prisms didn't come today like they were supposed to. I guess you can't expect those sort of things to come on time. I found a vinyl glove to use as a cushion between the base and the prisms. I attached the pattern I drew to the metal base. The glove is clear so the pattern is visible and I don't have to worry about that.
In the mean time I had to figure out other things to do. Matt and Joerg ran the bichro experiment today, apparently having resolved some issues with the polarization. I don't think the experiment was successful, however, Matt and Joerg really didn't expect it to be. Since I'm now working on Oleg's experiment, I sat in on their project meeting. I learned about Saturation Absorption Spectroscopy, which involves using rubidium atoms as a reference to stabilize a titanium sapphire laser. Matt Eardley and Mr. Lee were discussing reorganizing the setup to fit into a smaller space.
January 7, 2004
January 7, 2004. Today I worked out how to mount the four prisms. I also calculated their total magnification using right angle trigonometry and Snell's Law. Even though the math is pretty simple, when you're measuring angles you need a sense of direction. I now understand how anamorphic prisms work, and there's no great magic involved. The next step then, was finding the base. After searching through several drawers and rubble heaps I stumbled upon a metal base that's the perfect size with holes for screws in all four corners. I searched other drawers and rubble heaps and happened upon four screws that fit. I found a piece of plexiglass that was just the right size for the cover, however, due to a minor mishap, it is no longer usable. However, I was able to find a sheet that could be cut down. Now that that's all done, all we need is the prisms and we have our beam expander. I feel like I've had a fairly productive day.
January 6, 2004
January 6, 2004. It is now 2004. I went to federal jury duty in Brooklyn yesterday. Loads of fun. Fortunately or unfortunately (depending on who's reading this) I was not selected to serve on a jury. I had sushi for lunch yesterday, Ko Sushi, upper east side Manhattan, very fresh, I highly recommend it.
I finally found our prisms. I discovered very fast that anamorphic prism pairs generally only come in 12mm size made of glass that absorbs the UV wavelength. Littrow prisms come in the dimensions we want. They are most often used to tune laser cavities, however, without their reflective coating they can be used as large anamorphic prism pairs. I found a great deal from Edmund Optics in just the right glass in stock. They have now been ordered. Oleg and I ran up five flights of stairs in order to submit the proper form to the grant office before it closed. My legs hurt. I will soon be charged with mounting the new prisms, but until they arrive I will have to find other things to do. Dr. Noe of the Laser Teaching Center has bestowed upon me my first professional lab book. I guess I can try to figure out what to write in it.
December 29, 2003
December 29, 2003. I've been assigned the task of finding an anamorphic prism set for the Rydberg experiment. The laser beams that collimate the atomic beam need to be expanded in one direction only. A telescope using cylindrical lenses could be used, except it takes up too much space and is inflexible. After I find the prisms, I'll then have to mount them. It's nice to be on "vacation" finally, it's been a long, hard semester, but I've definitely enjoyed it and it's probably the most successful I've had to date. I certainly learned a lot about a lot of different things. I want to wish my Mom a happy birthday (it was on the 25th) and my brother Jeff whose 25th birthday is tomorrow the 30th.
December 12, 2003
December 12, 2003. Matt and Joerg ran the bichromatic laser experiment for the first time last night. We were in the lab until 2:30 AM. We did not see beam collimation like we expected, however, we did see something, though Matt isn't sure of what it is. Things really came together last night. Although I've only seen the past month or so of work, I can appreciate the kind of time, effort, and extreme patience it requires to produce an experiment like this. Atomic beam collimation has never been attempted before using a bichromatic laser, so I'm very honored to be witnessing a part of scientific history.
December 8, 2003
December 8, 2003. Congratulations to Oleg Kritsun on earning his Ph.D. This was my first time attending a thesis defense. It was quite an interesting experience. Oleg did such a good job that the committee only met for ten minutes. There was quite a party afterwards.