Journal

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Monday, June 28, 2004

Hello everyone, I'm Anirudh Ramesh. This is my first day at the Laser Teaching Center. I'm known notoriously for not updating my journal, so don't expect long entries or even daily entries. I will try to summarize everything I've done in a day in 25 words or less. Unless I'm doing something that it is crucial to my actual project, I won't really be updating at length. For lengthier updates on our day to day occurrences, please check out Matt's, Danielle's or Jon's journals.

Today, we worked on magnifying glass focal lengths and image sizes and we sat in on a real Physics seminar. A speaker came from UMich and gave a presentation on EDM (Electric Dipole Moment) using Radon. It was quite complicated physics but the generic topic of the presentation was the distance between a dipole which is established in an electron, which comes out to the order of 1X10^-27 (epsilon.) We also learned that physicists like to A) measure the value of zero as well as B) Symmetry (Time, Charge, and Parity). So all I can say is that there's a lot to learn.

Tuesday, June 29, 2004

Today, we conducted more preliminary experiments and began some preliminary research. We learned about diopters and eyeglasses. 1 Diopter = 1 inverse meter. S = r(theta) .. quite an important formula for determining the angular diameter of celestial bodies etc. That's all for today folks.

Wednesday, June 30, 2004

Today we received a great lecture from Dr. Metcalf. He led us through the history of optics and E and M all the way up to the early 20th century with the discoveries of DeBroglie (pronounced De-Broy). It was a very informative talk which concluded with a discussion of how light conducts a force.

We fixed up our data from the eyeglass experiment by redoing the measurements more accurately, so we can consider that to be done. Another day, another entry.

Thursday, July 1st, 2004

I've spent much of this day trying to master Linux and html. For all of you who don't know, the Laser Center runs on an operating system called Linux, which is slightly more complicated to use than Windows. Html has been an adventure for me because I generally hate programming code. I've disliked programming ever since I took a class on QBASIC. Anyway, updating this journal requires a pretty good knowledge of html.

We had our first Pizza Thursday today. It was nice just sitting around and discussing things. Research is continuing. Oh yes, I saw an original printing of Isaac Newton's "Opticks," which was very interesting. It is around 300 years old... anyway, that's it for today.

Oh wait, I'm currently battling with an 8-layered Towers of Hanoi puzzle. I've been working on it with Jon for some time now. I shall conquer, eventually at least.

Friday, July 2nd, 2004

I HAVE CONQUERED THE TOWERS OF HANOI. After working on it for some time yesterday, I came in today and I solved it in 5 minutes... I guess I needed a fresh perspective. That's my success story of the day.

We had a couple of very informative talks today, one from Dr. Metcalf and another one from Jose, a graduate student at the lab. Jose taught us the mechanisms of a CCD Camera as well as how to use the software for the camera. Dr. Metcalf gave a wonderful lecture which involved first determining that a very specific frequency of light is required to bump an electron up to a higher energy level. Next, he spoke about the Doppler Effect, which further complicated the search for a specific frequency of. He concluded by speaking about optical molasses and Laser Cooling, phenomenons that are both caused by the resistance brought about by velocity dependent forces (such as friction) that contradict the direction of motion. Check out Jon's journal for more.

Week in Review -- Week Number 1 -- June 28th to July 2nd

Although I may make it seem as if all I've done is attended lectures and played the Towers of Hanoi puzzle, I have done A LOT of reading already. Each day, I focused on a different aspect of Optics. I'm trying to learn as much about the subject as possible and then focus in on a single area of the subject to conduct some meaningful research. Since before the program started, I've had an acute interest in Optical Tweezers, specifically their biological applications. I spent my first two days researching Optical Tweezers, finding out how the actual phenomenon occurred. I feel that I have a strong understanding of the concept of optical tweezers and how the actual optical trap is performed. I still need to learn a few things such as the Calibration of the optical trap. I have a couple of ideas about improvement of the setup as well as using the setup for some very far-fetched biological applications (These ideas are still on the drawing board, which means I'm still thinking about them). I have a lot of background on DNA molecules and PCR, which is one of the ideas I have about incorporating the Optical Tweezers with biology. This project contains hundreds of confounding variables so is therefore still on the drawing board and may remain there. I have some other ideas that are not so crazy, but only time will tell if any of these projects are feasible.

The next thing that I have researched is diffraction using a diffraction grating. I spent some time shining a laser through a diffraction grating as well as studying diffraction in textbooks. I noticed some strange phenomenon, such as the even-odd band system, that Lidiya pointed out to me. This is something that Azure also seems to be working on. Also, single slit diffraction did not yield the results that I expected, namely a very bright central maximum. Rather, there were three bright bands in the center, followed by a gradual dimming of the bands. This bright central maximum is something that I hope to incorporate into the optical tweezers setup. So I spent most of the third day researching diffraction and interference. On Thursday, I researched different types of lasers. I looked up and learned about Light Emitting Diodes as well as Diode Lasers. I also learned about Interferometers and Oscilloscopes on Thursday. On Friday, Dr. Metcalf's lecture motivated me to do some research on Laser Cooling and Optical Molasses. I read about some of the experiments that have been conducted on Laser Cooling in some physics magazines. Well, that pretty much summarizes the research that I have conducted over the week, using a variety of sources such as the Internet, textbooks, magazines as well as hands-on experiments. In the future, I will spend more time researching the aspects of Optical Tweezers that I do not know and see whether or not it is feasible for me to conduct a project with biological applications. There are many variables that make a biological project difficult, but the project-making stage is still taking place. First I will try to implement methods to improve the Optical Tweezer setup and then try to use the Optical Trap to conduct some experiments. This seems to be the plan for the time being and I will keep working on preliminary research until I am ready to begin.

Tuesday, July 6th, 2004

The floor was waxed. Research was brought to a halt by what can only be described as a higher priority. But in any case, the lab looks brand new. We did all our research in the library today. The library is a tremendous resource.

Wednesday, July 7th, 2004

I did some more reading today. We were briefly amused by Danielle's knowledge of Linux, which you can see more of at Matt's journal . Rita gave a presentation today on controlling chaos with a Spatial Light Modulator (SLM). Using this expensive piece of equipment, Rita was able to achieve Generalized Synchronization. This means that she achieved a reduction in chaos even with different initial parameters. Actually, the synchronization can be considered an elimination of chaos because the patters with set initial parameters (feedback loop) and the patters with the varying initial parameters (open loop) yielded very similar graphs.

Thursday, July 8th, 2004

On Thursday, Kiko Galvez came from Colgate University and presented his research on laser modes. His research dealt with creating different laser modes using various diffraction gratings. For example, a forked grating yielded donut shaped modes. The next part of his research was to combine Hermite-Gauss (HG) modes with Laguerre-Gauss (LG) modes, which he accomplished by using a forked diffraction grating.

After Kiko's talk, I was quite confused with the whole subject of laser modes so I spent the rest of the day with Alex Ellis (who had luckily been visiting from Harvard), Azure and José who explained the concepts of polarization, laser modes. We also learned about the diffrences between LG and HG modes. Quite an educational afternoon.

Friday, July 9th, 2004

Today, Dr. Metcalf gave a talk on MOTs (Magneto Optical Traps). He basically gave us an introductory talk today, which dealt with the definition of an OpticalTrap as well as a brief history of magnets and magnetism. I was fine with the talk until we reached the concept of a Bohr Magneton. We learned that the numberof magnetic moments (vector that tells the strength and direction of a magnet) can only be an integer multiple of a Bohr Magneton... as you can see, this process needs to be clarified for me.

Week in Review -- Week Number 2 -- June 5th to July 9th

This week was a major learning week. On top of research that I conducted on my own, we were the beneficiaries of multiple lectures. Dr. Metcalf, Professor Galvez, José, Azure, Alex Ellis, and of course, Dr. Noé. All of these discussions added valuable firepower to our now growing arsenal of optics knowledge.

Monday, July 12th, 2004

Today was another big Laser Modes day. I think I've got that concept down finally. Laser Modes is a very interesting topic to study. We also updated Yaagnik today on all the stuff we had done during the last two weeks and we finally learned the series expansion for sine and cosine. We learned many good things aboutthe properties of light such as the Fermat Principle and Huygen's Principle.

Tuesday, July 13th, 2004

We received the second installment of the MOT lecture from Dr. Metcalf today. We learned many complex concepts of light, particularly the reasoning and equations behind light's angular momentum (which is a very misleading term... i prefer le synathique (it's French)). I left early on Tuesday so I didn't do too muchother stuff today other than some more light reading.

Wednesday, July 14th, 2004

José gave a great lecture today on the properties of lasers. We spoke about how a laser worked, Laser Modes, and many other things. Also we took a tourof the Van DerGraaf accelerator today as well as the Francium Lab. It was a great tour. We saw some very complex and dangerous stuff. The accelerator was very impressive.

Thursday, July 15th, 2004

Today is Pizza Thursday. It shall be fun. After pizza and a lot of other free food, I talked to Yiyi for a while and she confirmed my beliefs about the theory behind optical tweezers. I learned exactly how the change in momentum affected the trapped particle as well as definitions of the various forces acting on the particle. For example, I got a handle of the Gradient Force as well as the Scattering Force, which both play important roles in the trapping of a particle. Moreover, the Gradient Force must be greater than the Scattering force for the optical trap to be a successful one.

Friday, July 16th, 2004

Today was our second keg party. As usual, it was entertaining. Some new things that I've been researching are LG modes and angular momentum. I'm leaning towards a project where I can quantify the angular momentum exerted on a particle by a LG laser mode.

Week in Review -- Week Number 3 -- July 11th to July 16th

This week was, once again, a major research week. I've been narrowing down my preferred field of study and I think I want to focus on a tweezers setup involving LG modes (donut shaped beams).

We've also done some cool experiments this week. For example, we filled up a fish tank with corn syrup and then poured water dyed with food coloring on top of the thick layer of syrup. The water slowly diffused at the interface between the two substances and created a GRIN (Gradient Index of Refraction). When we shined a laser into the tank, it formed a parabola shape and looked like this (link will be up later).

Yiyi gave me a great lecture on optical tweezer theory. She straightened out many of my conceptions (and misconceptions). I think that I now have a good handle on the many of the various laser tweezer theories.

Hopefully I can start my project sometime next week. Yiyi will be demonstrating the optical tweezers setup on Tuesday to the other REU students so hopefully, after watching her run her setup, I can start on my own setup.

Monday, July 19th, 2004

Today, we made a Michelson Interferometer, an interferometer setup using two mirrors, a beam splitter, a laser and a lens. We felt that making an actual interferometer would further our concept of interferometry. Also, thanks to Azure, I found a great article on trapping using optical vortices by Grover Swartzlander , a man who I respect more and more every day.

Tuesday, July 20th, 2004

Today, Dr. Metcalf finished his series of lectures on MOTs. I must say that the eventual conclusion was quite elegant and somewhat disproportionate to the difficulty of the prior discussions. MOTs work on the concept of A) two opposing magnetic fields with a net force of 0 at the midpoint between the two loops (B fields cancel out at this point). B) The possible magnetic moments (orientations in space of the inherent magnetic fields of atoms) of the atoms in let's say a state of J = 1 (Total angular momentum = 1) all have different frequencies, meaning that different frequencies of light can excite atoms in one magnetic moment to another. The variation in energy betweeen states of different magnetic moments can be quantified by hf. Since the energy of these various magnetic moments causes a different force relationship between the energy state and the magnetic field created by the two coils of wire. C) Another important part of the MOT setup is the two opposing, propagating beams. The polarization of the light is crucial to exciting different states of magnetic moments. The interactions between all these factors, as well as a cross section of 6 laser beams, will create a MOT.

Wednesday, July 21th, 2004

Today was an overwhelming day to say the least. I was overloaded with information of all sorts that it made my head spin by the end of the day. First, we went on a tour of the CMM, which I found fascinating. All three departments that we visited, Structural Biology, Genetics, and Center for Infectious Diseases, were incredible. Upon noticing my interest in structural biology, Yiyi and Azure once again made their sales pitch and tried to deter me from Medicine. I must say that today's tour confused me a bit because I realized that doing physics/biology research would be very satisfying and enjoyable. So this was the first thing that I had to think about.

Secondly, Lidiya gave us a talk on Fourier Analysis and Transforms, which is just a method of expressing complex wave functions with sine and cosine functions. The equations that were used to let's say depict a square function in terms of sine and cosine were very complicated. But, I was able to understand the major concepts of the topic. However, this understanding did not come easily, and this was the second heavy topic I had to think about.

After Fourier and thinking about the future, I sat down and talked with Azure for a while and discussed my proposed project. I really began to realize my lack of knowledge in some particular subject areas, specifically angular momentum, a term that has lost all meaning to me. Moreover, I learned that I would be unable to use the forked diffraction grating because of the power of the laser. Instead, I may have to use either a phase ramp (which I don't know where I can get) or a setup of lens that converts HG modes into LG (like the setup Alex used). We also talked about the physical problems that I am sure to encounter (making LG modes, possibly polarizing the light circularly, and of course, trapping the particle) and then there are theoretical problems (The forces caused by an LG mode can't possibly be the same as the force caused by a Gaussian beam because the LG mode causes the particle to revolve on a Centripetal orbit... I shall have to do more investigation on theory, which I thoroughly enjoy except for the fact that it occupies a lot of time). Then there are problems I am sure to encounter in terms of calculations (Orbital Angular Momentum seems like a foreign concept to me even though I've studied it a lot... I will eventually have to see Dr. Metcalf and ask him to clarify this topic). So, all these factors added up to a MASSIVE headache.

Thursday, July 22th, 2004

Pizza Thursday today was great. Dr. Metcalf asked all of us about our projects and gave us some good suggestions on what to do. He also inspired us a bit to get our projects up and running. After lunch, we got another great lecture from José. He talked about how laser diodes worked and answered some of our other questions.

I've gathered a bunch of articles on the Orbital Angular Momentum (OAM) of photons and other experiments similar to my project, which I plan on reading this weekend. Hopefully, they will give me a better handle over the concepts involved in tweezing with LG Modes. This technique of spinning particles in an orbit is actually called OPTICAL SPANNERS (or OPTICAL WRENCH in America). There's a lot of research on this subject, so I plan on reading various papers and getting ideas that I will implement into my project.

Friday, July 23th, 2004

Today, José made a Mach-Zender interferometer, which was very interesting to watch. I read a lot of articles on Orbital Angular Momentum and I've gained a better handle on the whole concept of OAM.

We went to the physics keg today, which was entertaining as usual. Since we were in the Pit on Friday (due to the rain), I wanted to walk up to the blackboard and start writing random physics/calculus formulas. I'm sure it would've drawn the attention of the entire physics department, but I don't know how I would've followed up on the concept, especially when someone asked me what I was doing.

Week in Review -- Week Number 4 -- July 19th to July 23th

I made significant progress this week in realizing what I will actually be trying to accomplish for my project. I want to use LG laser modes (of different azimuthal charge) to trap and revolve particles. I want to first of all, compare the trapping efficiencies of the various LG modes, and possibly, compare it to a regular Gaussian Beam. Once I trap and revolve the particle, I wish to quantify the Angular Momentum that the particle gains. After this is done, I want to experiment with polarization of the light to see whether or not I can both rotate and revolve the particle. I will experiment with both left and right circular polarization and see if I can recognize the Angular Doppler shift of the particle that will be caused if I use circularly polarized light. Since light that is circularly polarized carries an Spin Angular Momentum of either plus or minus 1, I can calculate the total angular momentum of various LG beams with different Azimuthal charges (Total Angular Momentum = Spin + Orbital Angular Momentum) and OAM is equal to the azimuthal charge times h bar.

So, I wish to trap the particle, revolve it and measure Angular Momentum that the particle has gained, slow it down and speed it up (by changing circular polarization) and stop it completely (by cancelling the LG 0,1 mode with right cirularly polarized light (with an SAM of -1). I also wish to make a comparison between the change in LG mode in the microscope objective to the particle's gained Angular Momentum.

These are just my ambitious plans as of the end of week 4, but I'll be working hard on it. Once I can trap the particle, the other parts of the experiment involve just adding or subtracting the polarizer or moving the forked grating. Time will be a major constraint though, so I need to get started as soon as possible.

Week in Review -- Week Number 5 -- July 26th to July 30th

For the last week, I've been spending most of my time reading Azure's Optical Vortices book. This book is an incredible resource and is incredibly pertinent to my project. After I did my quota of reading for the day, I spent some more time playing with the Optical Tweezers setup, specifically the camera, objective and lens setup. Yaagnik and I worked on the mathematics of the setup, and Dr. Noe explained the mathematics of an objective focused at infinity to us. We compared the biological sample under the microscope objective to the sun and used angular diameters to figure out the magnification of the objective and the lens. I'm glad we got a refresher in the concepts of the sun and angular diameter and I learned how pertinent it could be to other concepts. Now that we've discovered the secret behind the camera focused at infinity and mathematically predicted the magnification of the sample, I feel that I have a better handle on the microscope-lens-camera system.

Wednesday, August 4th, 2004

I've been playing with the optical tweezers setup for about a week now. I haven't been able to trap with the gaussian beam yet, but I think that just seeing the trap would be good for me. There are a lot of obstacles to viewing the optical trap. Many of the lenses and mirrors are dirty and have smudges on them. So I should consider cleaning the lenses and the infrared blockers. Also, I'm hoping to get a new 100mW laser, which would be crucial to trapping with LG beams.

Friday, August 6th, 2004

I wrote a brief summary about Cricket today because Dr. Noé's son expressed some interest in the game. So in case you're curious, here is my cricket summary .

Monday, August 9th, 2004

I'm still playing around with the laser tweezers setup. It's been difficult trying to find the laser in the microscope's viewing field. Also, the dirt on each layer of optical devices between the CCD and the microscope slide causes the viewing field to be cloudy with other particles. However, the most difficult thing has been finding the laser.

Also, I tried to see what kinds of vortices I could make with the 20mW laser. The laser diameter was big enough that it covered all of the slits of the forked grating and as Azure had suggested, I allowed about a meter and a half for the vortices to expand. I was quite surprised when i took a look at the vortices that were being created. I'm not sure if they can actually be considered vortices because they were stretched vertically. There was some indication of a singularity in the first order donuts but outside that, the next orders just looked like a vertical line. I think it was because the forked grating was made for a 632 nm He-Ne laser and not for the 780nm laser that I used it with. However, the fact that vortices were not produced was disconcerting.

We did some revisiting into the world of thin lenses today. We wrote a report on it and there are some pictures as well.

Tuesday, August 10th, 2004

I began to wonder how I would make the vortices if I was unable to obtain a forked grating that suited the wavelength of an infrared laser. And I think that the best way to do it would be to obtain a spiral phase plate. So I'm hoping that Dr. Noé and I can start a correspondence with the Courtial Group in Glasgow, Scotland.

Wednesday, August 11th, 2004

Today I learned, much to my relief, that you could produce vortices using the forked grating and the diode laser. Apparently, the forked grating is not wavelength depended as I once assumed. The reason for this is because the pitch of the grating is much greater than the wavelength of light.

Thursday, August 19th, 2004

Yaagnik and I decided to team up to do our project today. We felt that it would be better if the both of us worked on the Optical Tweezers, because I had been having considerable trouble with the setup. So hopefully our partnership will be a fruitful one.

Thursday, September 16, 2004

This is the first day that I've been to the lab in a few weeks. School's been difficult. I thought that keeping my mind active all summer by going to the laser center would help me adapt more quickly to the school routine but, I feel mentally drained by school already. Yaagnik and I plan on accomplishing much of what we want to do between today and tomorrow. Outside of the LTC, I have been writing my portion of the paper and looking up additional journal articles to add to the background information. My science research teacher is pressing me to get some parts of the paper into his hands by Monday so I hope that I'll be able to show him something by then.

For now, it's off to work for 48 hours!!

Friday, September 17, 2004

Wow, what an interesting couple of days. Yaagnik and I got a lot of work done on the project, namely outlining and dividing the paper into sections that each of us will be writing in the near future. We also attempted to use mathematica to create our own forked gratings, something that we were unable to achieve. Moreover, we tried to learn LaTex but we were scared away by the error messages. We were able to create schematics of our setup in xfig as well as take some pictures of LG beams and our setup. In addition, we both gained greater control over the theoretical aspects of tweezers through the Optical Vortices book.

There were many funny moments over the course of the two day period, which can be found in detail on Jon's webpage. Sleeping on the floor of the lab was uncomfortable to say the least. I woke up with back, knee, ankle, neck, back, shoulder pain. But I exaggerate a bit. There weren't any lingering aches so no regrets here about sleeping the night over at the lab. On the other hand, the meal that we ate last night was a "fiasco" (In the words of the infinitely wise Yaagnik). But we were quite productive so it made it all worthit.

Now I know what it feels like to be a real physicist!