Saturday, October 20, 2007Because the data didn't come out as expected, Dr. Noe and I spent two very late nights with help from Marissa reworking the setup; we were very careful to consider everything (we hope!) that could affect the data in a negative way. We made sure that the beam stayed circular as it traveled towards the camera, and we used a mirror to more precisely determine where the center of the vortex was. With some trepidation, we took nine pictures with a step size of 10/1000 inches around the center. The data loosely followed a theoretical curve, which was very inspiring.
Because we liked what we saw, we took another 25 pictures. Starting at 300/1000 in. (the center's at 500/1000 in.), we worked our way up to 460/1000 in. at a step size of 20/1000 in. and then to 540 in. at a step size of 10/1000 in. and then to 700/1000 in. at a step size of 20/1000 in. again. I must admit that the intensity fluctuated dramatically towards the last few pictures, but theoretically this would not change the position of the centroid. This last set of data has yet to be analysed, but that will this week's project :)
Sunday, October 14, 2007Yesterday the lab was feverish with activity. Hamsa's parents and my mother were conversing while we worked on our projects, and Dr. Noe hurried between us. I no longer need to rely on the clumsy stacks of books and the somewhat broken mirrors to direct the laser beam to the camera. I commandeered Hamsa's old laser and built my own mode converter a la Hamsa, using one of her own hairs. After tinkering a little with it, I managed to produce a very nice vortex. The camera was then attached to a translator.
After that, Dr. Noe and I spent the better part of the night taking 43 pictures of the vortex beam while the translator (and therefore the camera) was moved to scan across it. The better part of the night was actually almost four hours! Dr. Noe was kind enough to stay until 2:30 am (and this was after a long drive from upstate -- where he brought us some delicious apples). Finally I went to bed at 3:30 but slept late, and enjoyed today's Oyster Fest in my hometown. A great weekend!
Sunday, October 7, 2007It turns out that the previous calculations for the centroids were just warm-up exercises! We came to the conclusion that the equipment may not be necessary after all, when you've got... A Hot Glue Gun by your side! The pinhole, camera, and lens can all be connected without the use of extension tubes or the like. Because the pinhole was glued to the case of the camera lens, it may not be completely on center. But as a lens has the capability that it focuses all incoming (parallel) light to a single spot, it hardly matters.
Next week it's back to centroid calculations (and more late nights--Hamsa and I clocked out at 1:15 am!).
Friday, September 14, 2007There have been a lot of late nights and two very productive lab days this past week. We did our test experiment, and the plot of the centroid values is in the last journal entry below (in case you missed it :-) . Here are a few more details (from a report I wrote to Dr. Noe):
A method was developed for calculating the centroids of the 11 ASCII files. The files were imported onto Quattro Pro, a spreadsheet program built for DOS computers. A "box" was placed around what we considered "relevant" data, or data that we thought the spot affected. The relevant data was chosen by identifying the highest-valued pixel and then by marking off pixels that were closer than or as far as 5 pixels away from the highest-valued pixel. The rest of the data was considered "background," in that the spot was considered not to seriously affect the data. The average of all background values was subtracted from each entry in the 11x11 grid of relevant data. Then the centroids were calculated.
Today I put some of the items in the Thorlabs catalogue on an Excel spreadsheet, to present to the purchasing department.
Next Saturday I'm planning on finally inserting an optical vortex in the set-up and sampling a few points on it. It will be exciting-- hope school goes fast this week! (although it may not because it is the first "full week").
Thursday, September 13, 2007Wow, look at this great new plot from our SHtest experiment.
Wednesday, September 5, 2007School starts tomorrow! The fun that we all had this summer is over. But there are always weekends :)
Yesterday Dr. Noe and I were worried that the intensity distribution of the laser over the first pinhole was not uniform, thus compromising the integrity of the centroid. In order to circumvent this problem, we made the distance from the pinhole to the laser greater so that the beam would expand. The intensity distribution in the middle of the expanded beam is much more uniform than the distribution in the beam's unexpanded form. While we did this, we inserted two mirrors into the set-up so that we could "walk the beam" into the centers of the two pinholes. Once the exposure time was adjusted to a desirable amount (50ms), we took 11 pictures of the spot as the first pinhole was translated in 50 micron step sizes.
Today we converted the image to a grid of values with one value per pixel, and calculated the centroid of the first and last image. Unfortunately, I had to leave early so I was not able to calculate the centroids of the rest of the images.
Friday, August 31, 2007Going through the Thorlabs catalogue to go "shopping" was kind of fun. Although what I needed to find was rather specific, it was neat to see so much optics all together. I was impressed at the organization of the catalogue and its way of advertising, their "application ideas!" were quite appealing. Once some of the necessary equipment was found, Dr. Noe suggested that I use the measurements given in the catalogue to see what sizes I needed so that the length of the set-up was approximately equal to the focal length of the lens I'll use in the experiment. I drew a rough sketch and found that there are several ways to mix and match the equipment. We still haven't decided which way is best.
I'm excited that school's starting again. I haven't seen many of my friends this summer and am eager to talk to them once more (I have already heard a few interesting stories, including one friend's tale that illustrates what it's like to be a beauty pageant finalist!).
Wednesday, August 29, 2007It's been a short while since I've updated this journal, but I was at another chess match, this time in exciting Washington D.C. Of course, there wasn't much time to sightsee between matches :)
Back at the lab yesterday and today, we placed a 50 micron pinhole in front of the HeNe laser to disperse and thus attenuate the amount of light emitted by it. We did it this way so we didn't have to use the rather clumsy polarizers. We then translated the pinhole slightly to simulate a wavefront tilt. We found that the spot does move, and by the expected amount. Good news! I'm now setting up a translator to translate the pinhole slightly in a more controlled way.
Tonight I need to make an inventory of what I need for the experiment, and tomorrow we might order the necessary equipment. I'm looking forward to finally using an optical vortex beam to supply the wavefront for the experiment.
And we're going to have to take a lot more pictures in the next two days before I leave once more for the last chess match of the summer ;)
Thursday, August 23, 2007Today, the light bulb that I had been previously working with was replaced by a laser. We attached a 500 micron pinhole to a lensholder, and placed it in front of the 8mm focal length camera lens in order to simulate the case where there is no wavefront tilt, the plane-wavefront case. When first looking at the computer, the spot size seemed suprisingly manageable; I just reduced the exposure time for the camera to bring all the pixel values below their highest value of 256, and I obtained a decent spot.
However, Dr. Noe pointed out that the "spot" I was looking at was far removed from the actual spot. After opening the aperture wider, I saw the computer screen get much brighter, producing a blooming effect where the center of the beam hit the CCD chip. I could not bring all of the pixels to under their maximum value, so I needed to reduce the amount of light the laser was producing. To do this I used two linear polarizers, rotating both of them until their directions of polarization were nearly perpendicular. The intensity of the spot size decreased dramatically, but even so I had to lower the exposure time to 4ms to guarantee that none of the pixels were saturated.
I had just enough time to save the picture before taking the train home.
Wednesday, August 22, 2007For the first time since the end of the Simons program, Simone, Hamsa, and I were together again. It was just like old times.
Today, we replaced the 100mm focal length lens with a lens of an ordinary camera (one that you would take pictures from) that has a much smaller focal length of 8mm, demagnifying the incident light (from the pinhole) greatly. We did not change the light source (a light bulb) or the size of the pinhole (100 microns). The distance from the pinhole to the lens is 54 inches. The light was focused and the exposure time was originally set to 100 ms. The camera's lens holder contains an adjustable aperture that we had discoved was triangular. The spot was reduced to as little as one pixel, not counting diffraction.
To make a bigger spot, we increased the exposure time to 1000 ms (1 second). As the exposure time increased, however, so did the noise from backround light and so called "hot spots", pixels from which a significant leak current flows (The computer assigns a value for each pixel based on the current that results from the many thousands of electrons in each pixel). We took a picture of the backround noise without the spot so we could calibrate the picture of the spot with the noise in the future. A grid of the values of the pixels was made on a separate computer. We placed a 500 micron pinhole directly in front of the lens but the amount of light passing through the pinhole was too small as the image was not detected on the CCD camera chip.
The pictures can be viewed here.
Tuesday, August 21, 2007We had used an incandescent light bulb with a pinhole and then a lens to look at the spot of light on the CCD camera. The camera is very sensitive to the light, creating what is known as a "blooming" effect, where the light from one pixel "spills" into the adjacent cells. We were able to create a spot of about 5x5 pixels with each pixel at least half the maximum intensity allowed.
When examining the particulars of the CCD camera, I noticed that given the number of pixels and the dimensions of the chip, the pixel size did not match that given. Therefore we set out to measure the pixel size using the diffraction of laser light off the camera chip. The pattern was viewed in relative darkness so I could mark the (in this case) green dots on the wall facing the chip.
After determining the distance between the dots and the distance from the chip to the wall, I could determine the distance between each pixel with a reasonable amount of error. The experimental distance was not far off from the given one. We discovered that the information concerning the dimensions of the chip were faulty. Another web site gave more precise dimensions that fit well with our experimental results.
Monday, August 20, 2007I'm back from a chess tournament and a few days at the beach (where I froze), and I'm ready to work in the lab all week on my maxi-project.
The last day at Simons went really well. I was a lot more relaxed in front of the parents and, although shaking a little bit, seemed to sound naturally confident (or maybe my mom was being kind :) . All the Simons kids are working on exciting things, and they showed how much fun they've had in their presentations. I'll miss the social life in the dorms--we had a good time every night!
Yesterday I read a paper on Hartmann/Shack-Hartmann sensors Dr. Noe kindly sent. Today I'll try to set up my experiment, which probably won't happen just yet as I need to learn a little more about the CCD camera I'm using.
Thursday, August 9, 2007It has been very hectic around the lab this past week. With abstracts due and presentations to write, there has been little time for anything else. Luckily, my abstract was done on time, although this may not have been possible without Dr. Noe's help.
Today, all of us tried our luck at speaking about our projects two minutes at a time. At first we failed miserably, but, by the end of the day, we were doing much better. It is now time to hone what we truly want to say and avoid stumbling. Hopefully it will all go over well tomorrow.
Tuesday, August 7, 2007Presentations were today. My prediction came true. I had trouble like the REU's did the first time they practiced; I was timid, slow, and struggling to find the right words. Although it didn't go nearly as well as I would have liked, it was by no means absolutely terrible. After the talks we showed the Simons Fellows into the lab and let them play with the optics. They seemed to enjoy it and we had a good time all around.
Friday, August 3, 2007The REU's came in all dressed up to look good for their talks. Our REU's were much more confident than before and gave great presentations. After we listened to Mallory, Ian, and Dan we had a great lunch (roast beef wraps with pasta salad, pickles, and chocolate chip cookies). Back at the lab Simone, Hamsa, and I thought about our abstracts and how we would have to work fast to get everything done. I hope I get a chance to practice presenting, or I might sound like the REU's the first time they presented!
Thursday, August 2, 2007The REU's gave a few practice talks today to prepare for their actual ones on Friday. Their presentations were a bit incomplete, they were a bit nervous, and they were struggling a little to find the right words to say. Of course, being a friendly audience, we helped them out by giving them suggestions and plenty of questions about the material they presented. The dilemma the REU's are facing now is a reminder for us high schoolers that we will have the same problem. Abstracts are due Monday and our own presentations are scheduled for Tuesday.
Thus I have only four days to complete both, definitely not an easy task!
Monday, July 30, 2007Today we had the chance to meet a man whose name frequently appears on the optics papers that we LTC students read: Kiko Galvez.
Last night I read a paper entitled "Non-integral vortex structures in diffracted light beams," and was surprised that Kiko devoted much of his talk to fractional vortices. He also brought along his daughter, who we had the pleasure of meeting as well. She had been in Peru, and is a rising senior so we all had plenty to talk about.
As far as my project goes, I will make a number of hypothetical calculations to get a good sense of how to go about setting up my project. Next week the abstracts for our projects are due and we are expected to present them as well... The three of us grow increasingly nervous each day.
Thursday, July 26, 2007The Simons Fellows had a meeting today all about the college application process. The difference between this lecture and all the previous ones we have heard (about this process) is that our speaker was not just an admissions person but a geo-physicist too. For us at the LTC, it happened to be our second pizza lunch in a row, which is always nice.
Afterwards, I continued to look into the tilt angle project which will probably become my "maxi-project." Dr. Noe and I discussed the possibility of using a pinhole array instead of a single pinhole, an idea that may or may not work out. While mulling over this idea, I found an excellent website that sells pinhole arrays for as low as $15 an array.
Meanwhile, the LTC just borrowed a four-foot, 38 mW, 632.8nm HeNe laser. Hamsa seems to have her eyes set on it, already giving it a few nicknames.
Wednesday, July 25, 2007Today, all the members of every optics lab had the chance to meet "Laser" Sam. His train arrived a little after 12:30, and he promptly started his very detailed talk about lasers. A total of 21 people crammed into the conference room, quickly gobbling up five pizza pies.
Lasers come in four types: diode lasers, gas lasers, solid state lasers, and liquid (dye) lasers. He mostly talked about the first three types dismissing liquid lasers as "messy." After the talk he visited the lab and took a look at a few experiments. Simone and I got a chance to practice explaining our mini-project. I guess it went pretty well as Sam understood all of it (not by any brilliance on our part of course :)
The LaTeX image is up and can be seen by clicking here.
Tuesday, July 24, 2007About a hour after I entered the lab I was informed that a troop of REU students was coming to visit the lab. This left Hamsa, Simone, and I to quickly set up our experiments. Simone and I finished putting our laser alignment setup together twenty minutes before the REU student's waltzed in.
As for poor Hamsa, she decided that her tweezers weren't at their best because of the faulty alignment of the beam and took the whole setup apart an hour before the REU's came. The three of us quickly tried to align the beam in time, but it required much more time than an hour to realign Hamsa's complicated setup. Despite missing the chance to control the movements of dead yeast cells, the REU's still had fun exploring the lab and playing with five other experiments.
Most of the afternoon was spent working on the tweezers, but I did get the chance to talk to Dr. Noe about a possible project that would measure the tilt angle (sometimes referred to as a skew angle) of a helical wavefront (probably from a vortex) using a lens, a pinhole, and a CCD camera. The LaTeX portion of the mini-project seems to be done; it was converted to an image that will shortly be put on the web. Even though it took us the greater part of the summer to complete our mini-project, I'm sure it was well worth the time, as we both learned a tremendous amount about research and how to conduct it.
Friday, July 20, 2007The lab report is essentially complete. All diagrams have been inserted and the conclusion is finished; however, Dr. Noe did not particularly like the introduction. The three of us cleaned it up and fixed all other problems in the body of the paper. All that remains is the editing, which we'll have done Monday. Now I can devote most of my energy into my "maxi-project".
There's a beer keg party today, but I'm going to have to miss it for two reasons: I'm leaving early, and I'm underage :)
Thursday, July 19, 2007Yesterday Simone and I were asked to present our mini-project.
I was a bit nervous presenting in front of the same group that had previously presented their projects to us. We did not come up to their standards at all, but everyone gave us plenty of encouragement, and that might have made up the difference. Hal's questioning inflicted us with the sense that we did not fully understand some of the subtleties in our project.
When we started the lab write up today, however, we looked over the entirety of our project again and better understood all that we had done. The actual writing part of our report is almost done, just the conclusion to go, but we still have to place all the diagrams in. Hopefully by Friday we'll be finished.
Tuesday, July 17, 2007Our lab-write is coming along pretty well. Simone created two xfig's graphs that show the schematics of the experimental setup and our linear one. Dr. Noe explained some more aspects of Linux, mostly relating to images and pictures.
At about 12:00 all the Simons students and the REUs went to the MARIACHI center. We heard professor Tom Hemmick make light of how the early universe was formed, and why physicists believe that the big bang model is a bit inaccurate and should be called "the big splash," denoting the presence of a super hot liquid commonly referred to as a quark-gluon soup. Dr. Noe advised us that to get elegant equations for the paper we would need to use LaTeX, a typesetting program. I plan to read a couple of chapters in a book I borrowed from Dr. Noe to get the hang of it.
Monday, July 16, 2007The measurements did not come out well at all, however, both Simone and I failed to record the distances between the mirrors, pinholes, and laser before the assembly was dismantled by Hamsa, so the measurements didn't matter anyway.
On the upside we finally found a recursive formula for how the distances should converge (with a lot of help from Dr. Noe). We created a graph of some hypothetical starting values using Quattro-pro, and got six really nice graphs, spirals and zig-zags. Tomorrow we will start the actual lab write-up.
Friday, July 13, 2007Today Simone and I took a few measurements, but it took so long that we didn't get a chance to plug them into our equations. I think by the look of my measurements they didn't come out so well... That just means I will have to do it over again and be a little more precise. As far as my "maxi" project is concerned, I still have very little to show.
Thursday, July 12, 2007Over the last couple of days Hamsa, Simone, and I were present for a couple of lectures. Thien An talked about how to derive equations to express Gaussian mode, explaining the dell, gradient, and divergence along the way. Yancey talked about diode lasers, a concept that I did not understand too well...
Simone and I have been working on our mini-project even more furiously than before. I think I found the solution today. It seems a bit simple but I can't see a refutation other than the fact that I assume the small angle approximation . As far as my actual project, I have a few ideas but they are in their infancy. Hopefully, I can find something ... and fast!!
Friday, July 6, 2007Simone and I worked hard on our mini-project. We came up with an algorithm which seems to work, although Simone had to convince me for some time that it made sense. So, all we have to do is the math to go with Simone's diagrams.
Dr. Noe introduced us to Quattro-Pro, a program similar to Excel in that it has rows and columns labeled with letters and numbers, which can store data and reproduce it on a graph. Using some hypothetical numbers, he showed that the graph of the distances from the photodetector represented the y axis and the distance from the iris represented the x axis.
Thursday, July 5, 2007Today we had our long awaited field trip to Brookhaven Lab! We saw the RHIC and there were two big tubes that encased a beam of gold ions that had a thickness about the width of a human hair. The extra space that the tubes enclosed consisted of pipes in which liquid helium flowed to cool the superconducting magnets.
We also looked at the STAR experiment. The two beams in the two tubes came together in a huge metal container that was really the size of a room in diameter. There was a camera inside that took pictures of the particle collisions. It was fun to finally see the Brookhaven site.
Tuesday, July 3, 2007Today, as fate would have it, Simone and I are partners. This will not last forever, as we are working on a mini-project, an interesting one that gives us a chance to use some of our math ability.
On Monday, Dr. Noe challenged Simone and me to align a laser beam through a makeshift pinhole (an iris) into a photodetector. We could use only a laser and two mirrors (stands, levels, screws, and screwdrivers were all permitted). After fiddling around for quite a long time, we got pretty close, and Dr. Noe looked pleased the next day (I hope!).
He still had to tell us, however, how all the knobs worked and the proper procedure for aligning the beam. We learned that our frustrations the day before were due to a particular fact. If one adjusts any of the mirrors, the position of the light on the iris and the angle of the light going through the iris changes. It turns out that if one adjusts the further mirror (with respect to the iris), the effect on the light's position is more pronounced than that of its angle of incidence on the iris. The opposite is true if one adjusts the closer mirror.
Thus the procedure is to alternate adjusting the mirrors, focusing the light on the center of the iris if adjusting the first mirror, and focusing the light on the center of the photodetector if adjusting the second. The reason that one alternates between mirrors is that by adjusting one mirror, one also changes the position of the light away from the center of the iris or photodetector that the other mirror had sought to fix, but by a lesser degree. After a lot of adjustments, the alignment will be near perfect. Our mini-project consists of finding the distances that the light moved (away from the center) each time a mirror was adjusted, and to see how these distances converge to zero. So far, we're off to a good start.
July 4th should be a blast (fireworks), but I'm also looking forward to the tour of Brookhaven National Lab, which houses a giant particle accelerator. It should be fun.
Friday, June 29, 2007On Thursday Dan finished the rest of his talk about geometrical optics by giving a thickness "t" to an ideal lens. This new thick lens contains two principle planes commonly given the names H1 and H2, and two nodes, N1 and N2. The principle planes serve as surfaces where refraction can occur instead of at the lens' surface. Note that refraction does not actually occur at the principle planes, but it makes ray tracing easy in that using the principle planes the incoming light ray exits the lens the same way it would have if it refracted off the surfaces of the lens itself.
The nodes have the interesting property that if a light ray hits the first node at some angle, the light ray comes out of the second node at that same angle. It also seems that a light ray can be described by two properties, its height and its angle. These can change when the light ray interacts with its environment and are described totally by three matrices, one for translation, one for reflection, and one for refraction.
Simone and I were still struggling to find a mini- project as we did not even know what to search for! Dr. Noe told us what kinds of experiments would be considered mini-projects, so now we have some ideas. Simone wants to do something with gravitational lensing (she is fascinated by relativity, time paradoxes, cause and effect relationships, etc).
Dr. Noe suggested that I determine the restoring force equation of a rubber band and the restoring force equation of a mirror stand so that one could pull on the rubber band a certain distance causing the mirror stand to move a little distance itself. The idea is to adjust the interference pattern in an interferometer precisely. Hamsa has suggested that I work with optical vortices. I think I'll try the rubber band project first, then, if it doesn't go well, I will switch over to optical vortices.
Wednesday, June 27, 2007This is the start of my journal, so here it goes. In the first two days of my time here at the Laser Teaching Center I have already learned a lot. Yesterday Dan D'Orazio gave a talk about geometrical optics which included the derivations of two very fundamental laws of optics, the law of reflection and Snell's law.
Today, Urszula and Hamsa talked about their work on "optical tweezers". I'd write more, but I've got to go back to the dorms (they've got really strict rules :( ), but I'm really looking forward to the next couple of days at the LTC.