July 10, 2003

Today, I found a whole slew of new sources about CBS. Particularly interesting was the article entitled "Studies of coherent backscattering from opal photonic crystals" by J.D. Huang et al., since it discussed opals and opalescence, the topic which got me interested in scattering phenomena in the first place. I also found "Calculations of the Soil Hot-Spot Effect Using the Coherent Backscattering Theory" by Liang and Mischenko that seems to have an interesting application of CBS. During a lull when I took a break from searching for articles, I learned about polarization and Jones Matrices by playing around with the long spring and wondering what circularly polarized light would look like. Tom and Jose helped to clarify how the matrices explained the polarizations, and by looking at them I realized how the different polarizing lenses and plates affect light.

Tonight, I plan to finish reading the article about Calculating Hot-Spots and then read teh article about opal photonic crystals. Hopefully tomorrow I'll be able to get a start setting up a CBS experiment to get some data and actually see how it works. I've found a large number of diagrams depicting the setup, and Ming Lu (a previous student at the lab) has some helpful pictures that describe his setup.

July 11, 2003

Today I got a laser and a place to work! I spent a lot of my time today cleaning the desk and trying to locate the instruments I need for a CBS experimental setup, like a beam splitter, 1/4-wave plate, mirror and polarizer. I may need to adjust the classical setup by adding something like a narrow tube to the detector in order to filter out background noise, etc. Before I actually gather any sort of data for my project, I need to learn exactly how each of the components of the setup functions. I know about the linear polarizer and lenses in the setup, but I'm not sure how a 1/4-wave plate circularly polarizes light, or even what circularly polarized light is, exactly. I also need to figure out how the detection mechanism works. It doesn't look too difficult, but I think I should know it well in order to accurately interpret any results. Below is the setup Ming used in his project, to give an idea of what the setup looks like (the image has been gratuitously stolen from his jounal):

July 14, 2003

Today was a sort of stream of tangents which ended on a constructive note. It began when Dr. Noe showed us that by inserting a polarizing lens at 45-degree angle between two linear polarizers at 90 degree angles to each other, one can see an image through the three lenses. By looking at the Jones Matrices for the lenses, I saw that this should work because a 45-degree polarizer between to linear polarizers prevents the matrices from multiplying out to the zero vector... but I wanted to know the relationship between the angle of the rotating polarizer (in the middle) and the amount of light let through. Pat and I designed an experiment using a phototdector and three polarizing lenses to measure the variation on the amount of current induced on the photodector by a laser (the laser I plan on using for my project), by the angle at which the rotating (middle) polarizer is situated. As we took down the data for the experiment, we noticed that the current kept fluctuating in the multimeter. The fluctuation was a little weird, so we decided to look at the output of the laser in the oscillator, and found that it was hashy... which didn't seem to make sense. During all this, I learnead about how the laser was built, the various modes that get gain inside the laser cavity, and how these modes could shift as the laser heats up. It turns out that it's the laser that was causing the fluctuations, but I don't think that should cause too many problems when I'm taking my data, I'll just have to keep it in mind when I have to look at and interpret the data. The graph below shows the results of our experiment, and the theoretical fit of the data (calculated by using the light's electric field as a vector and calculating the intensity based on the angle of incidence to each polarizer) I made using Gnuplot (which I learned today!):

July 16, 2003

Today Tom and I set up a scattering experiment in the back to measure the amount of laser-light scattered from the sample ceramic material he has. This setup is similar in many ways to the setup that I'm going to be using for my experiment. Today after the lunch meeting, I talked to Professor Metcalf about polarizers and Jones Matrices, and I think I have a pretty clear idea about how polarizers and materials that affect electric field orientation and phase operate on light. The next few things that I need to do are to figure out if I need to use a beam expander, and to figure out the distances in my setup. I also want to try to find information on fractal aggregates and any relatively accessible and safe aggregates that I could use for an experiment. Also, I want to email Professor Genack... which I haven't yet done to see if he has any input on a coherent backscattering project. Also, I'm going to write up a small website for the side experiments I did on polarizers and what I learned about Jones matrices.

July 17, 2003

Today I attended a fascinating lecture that Professor Metcalf gave on Quantum Mechanics. He clarified some of the questions I had about the wave equation which I read about in Jose's textbook, without even writing it out! I also worked on my experimental setup and began drawing it out on a piece of paper. I'll see if I can make a vector drawing of the projected setup on my computer to post up here, and I'll note the drawing in my lab journal. I also started working on a website about the experiment I did with polarizers, and a webpage about coherent backscattering that someone might find useful. I'll add a link to them once they're readable.

July 21, 2003

Today, Sage and I did a small scattering experiment using Tom's detector and sample to see what kind of data we would get, and try to interpret it. We definitely got some kind of curve, and tried to figure out what kind of theoretical curve to use to fit the data. A graph of our results, and a possible theoretical fit based on the sine of the angle between the detector and the sample can be found in Sage's journal. We made the graph using gnuplot, which is getting easier and easier to use everytime!

Also today I attended the second lecture Professor Metcalf gave on Quantum Mechanics. I understand a lot of it, but Quantum Mechanics is still very confusing since it dictates that you cannot ever get a definite answer from just the pure mathematics which describe nature. After the lecture, I continued working on my setup, and mapping out my space on the desk on a piece of paper so I know exactly what it should look like before I actually set it up

July 22, 2003

I haven't really had a chance to work on those two pages I want to make... I may be able to do that tonight and just email it to myself. I've also been trying to better understand the math behind the CBS effect; I found a slide presentation online which could help me to may help me. I've also been seeing a lot of the same math repeating in a lot of the papers I've read, which I'm slowly beginning to pick up on. I thin that once I understand the basics, I'll get the special derivations in each individual paper. I'll update my sources page when I get back to the dorms and put that up tonight. I still need to find out more about fractal aggregates to see if I want to use them in my project, and I need to continue working on my setup.

July 23, 2003

Today, Alex Ellis, a High School student who worked in the lab last year visited the Laser Center. He gave a presentation on his project on Astigmatic Laser Mode Conversion. We also talked about getting started with writing papers, and time management in general. He gave some pretty good advice about when to start writing my paper, and when to really start gunning with a project.

I also continued trying to understand the math behind CBS, and I understand why the enhancement factor was predicted to be about 2 in the theoretical model of CBS. It's because when two waves are in phase when being scattered back, their sum is squared, and when they are out of phase, their squares are summed, thus when the destructive waves are subtracted, a term with a factor of two is left over, predicting an enhancement of two. I still don't quite understand the major reason why the shape of the intensity distribution is conical, but I think I'll understand by the end of the week.

July 28, 2003

Today, after yet another mind-blowing Quantum Mechanics lecture which I thoroughly enjoyed, I spent some more time thinking about the theory behind my project. I really need to work on my setup, but I really want to understand the math behind it. I spent the day reading about photon diffusion approximation in various media. I found some more interesting articles with easier explanations and definitions which I'll post on my sources page when I get around to updating it. I've been working on my CBS page with the new information I've learned, but it's not yet complete. Today I looked at the pinhole which Doug Bennett used on his setup, and played around with it trying to figure out the size. I also spent some time looking at websites on photomultipliers to try and figure out how they work. I need to set up the pinhole, reflection screen and PMT up so I can figure out how to align everything to gather data. Reading about the problems that Ming and Doug had have helped me a lot in thinking about the setup, and the pictures they put up are also excellent. Tomorrow, I'll spend the morning trying to get a PMT for my setup, and working on aligning everything to get rid of weird reflections which seem to occur when the laser hits the beam-splitter and the quarter-wave plate. Also, I have to make sure the quarter wave plate is aligned correctly to circularly polarize light, and the linear polarizer is adjusted to prevent reflections from hitting the detection mechanism.

July 29, 2003

Quite a few good things happened today. Earlier, Jose took me to clean off the beam-splitter I'm using in my setup, and Oleg showed us the necessary steps needed in cleaning coated optical components. I wrote these down in my journal as they can prove to be useful later on. The best part about it, though, was that when I put the newly cleaned beam-splitter back into my setup, ALL of the reflections that were annoying me were gone, save the one from the quarter-wave plate.

Later, Jose gave us a talk on Lasers, Cavities/Stability, and Mode Structure/Gain. It was really interesting, and gave me a lot more insight and understanding into exactly how lasers function. After the talk, Mr. Schorn, my science research teacher came in to talk to me about my paper, and to visit the lab. We talked for a long while about my project, and I tried explaining to him what I was working on. After we felt that he had a pretty good understanding, we talked about deadlines and how I should organize my introduction. I think it's important that I get started as soon as possible in writing my paper, so that I don't have to worry about cramming the entire paper-writing session into a period of three nights.

July 30, 2003

Today, all the Simon's Fellows visited the Brookhaven National Laboratory. It was a great experience, as I got to see the Relativistic Heavy Ion Collider, National Synchotron Light Source, and the Van de Graaf Accelarator that they have over there. Upon our return, Jose finished the talks he started yesterday about different types of lasers and gaussian optics/beams. There's been so much information to absorb over the last two days, but I think that I've managed to grasp and understand most if not all of it. It may be worthwhile to try and explore/derive the math behind the different topics that Jose touched upon to try and gain an even deeper and more useful understanding. I also continued working on my setup.. and tried to figure out ways around the reflections and the severe loss of laser signal which I am going to have to deal with due to the reflections by the wave plate and linear polarizer.

August 4, 2003

August 28, 2003