July 26-August 1, 2010

On Monday we had the vortex party. It was very imformative because I don't know very much about laser modes. I was really impressed with the quality of Jacob's presentation. It has inspired a bit for my REU presentation. My presentation went very badly so I will need to make sure to be better prepared for the next one. I did get a little stressed about the how long the party took because I had so much to get done on my project.

I took data to show how circularly polarized my light is. There is about a 3 percent error but I still need to learn the Stokes parameters so I can better quantify its polarization. I also took data to show the effect of reflection off of a mirror. On Wednesday our abstracts were due. It was a little scary having the entire group read it but its good to get feedback. Dr. Noé and I worked a great deal on the abstract on Thursday and Friday and completed it so that's one less thing to worry about.

We have simplified my experiment a great deal. Now I am just looking at the Berry phase for a transformation from vertical linearly polarized to circularly polarized to linearly polarized at some angle and, finally, back to vertical linearly polarized. The closed path on the Poincaré sphere means that the Berry phase is equal to half the solid angle which is pretty easy to calculate. If I have time I want to try to do an open path but first I need to get some decent data for the closed path. We took some very good pictures of the phase shift going from the linear polarizer at 0, 35, and 70 degrees with respect to the vertical. I set up a translation stage to try and get some data for the exact amount that it shifted but the data was difficult to get because the movements are so small and the fringes aren't perfectly straight or perfectly defined. I gave up in frustration Sunday night but looking at the data now it's not as horrible as I had suspected. I thought we'd need to try a new method but I might be able to get good results this way if I work carefully and try larger intervals.

July 25, 2010

I came in over the weekend to get some more work done. I have gotten my best circularly polarized light to date and verified that there is a polarization change off of the mirrors and beamsplitters which means my ideas for changing the experiment won't help. However, I can use an initial polarization state that is vertically polarized which will allow me to get their most interesting results (the phase singularity). I started re-setting up my interferometer but still need to work on alignment to get fringes.

July 20, 2010

I have emailed one of the authors of the paper I'm trying to replicate but there hasn't been any word back yet. I have mounted the linear polarizers and quarter waveplates together to try to create circularly polarized light. It isn't quite perfect though and it's difficult to get them lined up quite right. I might need to adjust the calculations a little bit to accommodate for it. I have also set up the Mach Zehnder interferometer and gotten fringes (without the polarizing elements in place). I now need to start figuring out the polarization changes from the beamsplitters and mirrors. Dr. Noe suggested potentially adjusting the setup so that the polarization changes from the beamsplitters and mirrors aren't an issue. I am starting to think about this idea but I haven't settled on the perfect idea yet. I am going to be presenting about the experiment on Monday. I am a little nervous but hopefully Dr. Galvez and the others can help me although if I'm still not taking data by Monday I am going to be a worried. So little time left!

July 13, 2010

I successfully determined which of the quarter waveplates we found worked for my laser. Now I have enough retarders for the experiment. I was hoping that I would be able to start setting up. I began looking at the plethora of beamsplitters I have accrued over the past week. I began testing to see that the beamsplitters would split fairly evenly at my wavelength and then it dawned on me to look at the polarization of the beams after splitting the beams. The one beam went straight through with no affect on the polarization but the other one ended up eliptically polarized. This brought on the confusion I have been facing for the past few days. In the mathematics of the paper there is no consideration about the change in polarization from the beamsplitters. I believe there are ways to orient the beamsplitter so it doesn't cause a change in polarization so I need to read up on that. However, perhaps since both beams will experience the same phase shift from the beamsplitters (one beam from the first beamsplitter and the other beam from the second beamsplitter) but I'm not sure that's true.

While I was trying to figure out the beamsplitter situation I reread the paper again and ended up realising some confusion I have about the setup. The paper talks about creating an initial state that undergoes a series of polarization changes and once it's in its final state is recombined with a beam in the initial state. However, when I looked at the experimental setup only one of the beams is put in the "intial state" while the other is just left in the polarization created from the laser and beamsplitter. Therefore, it seems as though the final state is not being recombined with the initial state but with some other random state. No one I have asked seems to be able to answer me whether this matters in the experiment. I feel like it might but I don't understand it well enough yet to say. I just feel frustrated because I can't really proceed with my experiment until I know.

The two things I need to figure out a.s.a.p. so that I can start my experiment: whether the polarization change from the beamsplitters cancel out and can be ignored and whether both beams need to be put in the "inital polarization".

July 9, 2010

I started setting up my experiment a little bit. I found mirrors and polarizers and I have seen the drawer full of photodiodes. I wasn't able to find the binder with the catalog of lasers and power sources so I haven't been able to setup and test my laser. Also, I am not sure how to use a photodiode. Jacob was playing around with one but he wasn't entirely sure how to either. Additionally, I don't know where the CCD camera is or how to use it. However, the biggest set back has been quarter wave plates. I have found one and potentially a few others but Dr. Noe wants me to make my own as a side project. I don't mind playing around with making some out of cellophane but I'm worried that using them in the experiment will give me terrible results (and I'm already concerned about how good my results will be).

July 6, 2010

Metcalf gave the REU lecture this week. It was about the coldest temperature in the universe. He started by giving up an order of magnitude idea about temperatures in Kelvin: 300 on the surface of earth, 5000 on the surface of the sun, 30 liquefies gases (except He and H), 3 liquefies He, etc. Then he talked about laser cooling using a little quantum. You can show that the force exerted by a laser is proportional to minus the velocity thus it opposes the direction of motion and decreases as the velocity decreases. This cools up unto a point. Eventually the light can no longer transfer energy because it must be done in discrete packets. This gives a bottom limit to the lowest temperature that we can create in the lab. It was really interesting and Metcalf named one of the particles after me in his discussion.

I have decided to go ahead with the project I mentioned in my last entry. I hope that I might find some idea to maybe expand on the experiment but if I don't I will at least have gotten some experience conducting an experiment. I am trying to figure out what order to do everything in. I still need to do more reading to understand everything but I might need to start the experiment before I fully understand it in order to make sure it gets done. My other concern is that many materials are tied up in established setups, especially mirrors and such. Hopefully, there won't be too many conflicts over materials in the next few weeks.

July 2, 2010

Dr. Metcalf derived Fourier series from our talk about sound waves. It made a lot of sense and was a very different way of thinking about Fourier series, although a little less mathematically rigorous. Good way to learn the concept but you would have to go back and teach the way to solve for the coefficients.

I have an idea for a project. There's a really interesting paper (second link) about non-cyclic polarization changes. I enjoyed reading it and fully understanding it would involve understanding the Poincare sphere, Jones matrices, and Berry phase. I would like to try to replicate their results. The experimental setup isn't too difficult. It's based off of a Mach-Zehnder interferometer supplimented with two polarizers, two compensaters, an attenuater, a photodiode, and a CCD camera. I think I've seen or heard of most of these things being in the LTC. Hopefully, this is a possibility.

June 30, 2010

Vince gave a great talk about the wave nature of light. Most of the stuff I was familiar with but there were a few new insights that I gained. The first was prooving that rewriting cosine and sine in terms of exponentials was valid because they yeilded something that wasn't imaginary. The other thing was a different derivation of the two slit experiment.

At lunch we talked about sound and combining different frequencies of waves. It was very interesting because I generally have kept my music appreciation and physics very seperate from one another. We also talked about our interests and ideas for projects. Jacob was able to quickly coil one of the LTC's fiber optic cables around an empty jar and look at how the polarizatin changes (which is his project idea). We saw right away that adding or taking away a loop around the jar would change the final polarization. However, seeing such success already makes me a little wary. I need to choose a project soon! I need some time to just sit and read. Hopefully, I can do a little bit of that tomorrow.

June 29, 2010

Today I gave a talk for the high school kids to review some basic math that they'll need for optics. I think the talk went ok and they seemed to remember the material pretty well. The only thing they hadn't learned was the wave equation. Hopefully I didn't confuse them too much! I didn't explain it very fully because I really only wanted to give them an idea but I'm worried by not going a little more in depth it might have just left them confused.

We had an REU talk today where we were saw some simple REU projects from past years. They were pretty cool and easy to understand. The most interesting project was a tank of water with sugar at the bottom where the index of refraction would get higher the lower in the tank so the laser would bend and hit the bottom of the tank.

After lunch we finally got the Mach-Zehnder interferometer to work which was very exciting. It's a delicate business producing fringes however Prof. Metcalf said it gets easier each time you do it so it's a good thing I'm starting to get some experience. Other than that I didn't make any progess on choosing a topic. Hopefully, tomorrow I will have more time to do some reading since we have fewer commitments.

June 28,2010

The high school students arrived today so the first half of the day was spent going over the pig toy and some of the other things we covered in our first week here. We spent the second half of the day trying to build a Mach-Zehnder interferometer for Katya's experiment (Jacob might also use it for an experiment constructing a different kind of optical tweezers that rely on a polarization gradient). Unfortunately, we couldn't get the interferometer to work. We even tried changing its structure and using the already built Michelson interferometer to gain insight but we still didn't see any fringes. We're not really sure what's going wrong.

June 25, 2010

Still no chosen project but I have now found about 20 papers to read over the weekend, mostly by M.V. Berry or E.J. Galvez. There are a lot of different singularities besides just optical vortices (phase singularities). The reading has been very interesting but I don't really feel like I'm understanding much of it so I've carefully chosen articles and an order that will hopefully ensure that I have sufficient background to understand each subsequent article. I still feeel a little all over the place but hopefully sitting down and focusing over the weekend will fix that.

Today we all sat in on Dr. Metcalf's group meeting. I didn't understand much of the physics they discussed but that's only natural because they weren't explaining their projects just discussing them. Metcalf mentioned laserfest (celebrating the 50th anniversary of the laser) and told us to look it up. I looked it up briefly. I might try to organize some sort of event at Duke in the fall.

June 24, 2010

I wish I could report that I've chosen my project but unfortunately I feel ever farther away from making a decision. Dr. Noe and I had a really good conversation today which helped me at least choose a very broad topic of interest. From the reading I did from the Proceedings of SPIE conference on Complex Light and Optical Forces IV booklet, I think Berry phase might be an interesting topic to look into. I need to still read more about the phases and the Poincare sphere. I'm not sure what exactly I'll do as an experiment related to Berry phases but at least I feel like I have a direction. If I enjoy this stuff I might take a topology class next semester.

We also decided topics to present to the high school students when they get here. I was a little anxious because I don't feel qualified to be teaching anyone; however, I am doing math essentials so I think I'll be ok. I will need to brush up on where all of this stuff comes from because inquisitive minds love to ask why we can make approximations, etc. I just have to keep reminding myself that this is very casual so I don't need to get nervous. Hopefully I won't make any mistakes!

June 23, 2010

I have gotten a little farther on choosing specific projects however they still fall under the four big topics I mentioned before. Hopefully, I'll narrow it down to one project tomorrow. We had a group lunch to wish Justin farewell. It was wonderful to hear Dr. Metcalf speak! He comforted us about the confusing talk we had attended and started helping us get in the mindset to help the high school students when they get here. He also pulled me aside after lunch to talk to me about a journalism and communication in the sciences program at Stony Brook. Science is becoming a large part of everyday life and, especially when catastrophes strike like this oil spill with bp, the media needs someone knowledgable and eloquent to explain to the masses what is really going on. It's definitely something to think about, but for the time being I think physics graduate school is still my plan.

June 22, 2010

I still haven't exactly chosen my project but I'm working on narrowing it down. I have gotten it down to 4 possible topics: Fourier optics, negative index of refraction, optical tweezers, or sonoluminescense. Obviously all very different topics.

June 21, 2010

I learned a little bit about Linux today. Also, I'm learning how to update the website a little bit. Very cool.

Heather Hill
Summer 2010
Laser Teaching Center