Tuesday, November 1st
Summer is over and winter has emerged. Many new things have occured.
After the summer fellowship ended, I thought I only had a few days before the school year began. Soon, I was totally absorbed in my classwork. However, there have been a number of occurances since I made my last journal entry.
I worked with Dr. Noe on my scientific research paper, and submitted it into Siemens Competition in Math, Science and Technology. I became National Semifinalist a couple of weeks ago and I am now working on improving the paper for the Intel Science Talent Search Competition. It is due at mid-month.
By far them most interesting thing I've done since Simons is go to the Frontiers in Optics meeting in San Jose (which is near where I live). I left school early Friday to go to the convention center to attend the Undergraduate Symposium. I was able to find the place easily, but due to a mixup I had difficulty getting past the registration desk. The receptionist was extremely nice. When she heard that I was a high school student and I thought my professor had already registered for me, she was surprised and waived my $200 fee and let me in.
One of the first things I saw when entering the area for the poster presentations was Dr. Noe talking to a professor I didn't know. When Dr. Noe saw me, he exclaimed "There he is!" and introduced me to the distinguished physicist, Sir John Pendry. I was amazed because I just finished reading some of Pendry's papers in an attempt to improve my own paper. Unfortunately, I missed his planery talk, but I was able to find an online video recording of it later.
The conference was amazing! I met many important people, and many of the student projects were interesting and not too hard to understand.
Friday, August 13th
Today is the final day of the summer fellowship program. After oversleeping and hurrying to my lab to pick up my project, I went to the Wang Center to set up my poster display and prepare my presentations. I met several of my friends, and learned about what they were doing during their fellowships.
There was also time to go to the Garcia program's closing ceremony. Their refreshments were also an appealing draw.
After the ceremony, it was time to depart for home! (two-hour extremely cramped shuttle ride to the airport and a 6 hour flight returned me to my old existence. I felt some loss of leaving SUNY Stonybrook and my Simons fellowship)
Thursday, August 12th
I tried to sleep in the lab last night. Anybody who is reading this, make sure you bring warm clothing if you want to try this yourself. A sleeping bag would be reasonable, since that soft rocking chair only seems soft when you're sitting on it for less than an hour
My mind was focused on how the reflectivity of a normal glass prism compared to FTIR. It seems to be normal, since I'm losing about 10 % through reflections on the sides of my prism.
I took more data on the Fabry-Perot etalon and I saw how it varied with both angle and polarization. It seems like the relationship between these two variables and Fabry-Perot effect are related; they both work through reflectivity to change the shape and intensity of the fringes.
Dominic came to discuss my setup. I showed him the Excel spreadsheet which could be used to model the ATR reflected intensity drop. It looked similar to the curves he found in his research. We went through each variable and concluded that they were all correct. I think the most likely thing that could be wrong is the film thickness. If the piezoelectric crystal was placed too far from the gold film, it could have caused a the film to thicker that it said it was.
Wednesday, August 11th
Today, I went to the TLT center to print out my poster and got lost. The poster looks pretty good. I think 25 size font is appropriate for the poster. It allows you to stand a decent distance from the poster and still be able read it. Font size 30 should only be used for titles and headers.
I did a large data set on the whole angle spectrum and found that the reflectivity went down and then back up. I guess this means that reflectivity increased the more I slanted it, when I was reflecting off the mirror. As I increased further away, I was past the critical angle which makes some sense.
Since the reflectivity pattern was strange, I decided to go back to FTIR and test for the reflectivity, to see if the reflected and transmitted light matched. In theory, the light reflected from FTIR should go down to zero, but in actuality, the reflected signal is always larger than the transmitted signal. Even at the point of most transmittance, the reflected light is still an order of magnitude higher than the transmitted. The reason for this is unclear at this time.
The data I obtained from the experiment made sense; the reflected light did seem to decrease exponentially, although it was much harder to measure the evanescent wave through the reflected light.
Tuesday, August 10th
I was able to get the film done. When I tested it, no matter which parameters I varied, I was unable to get any significant change in intensity reflected. There were long trends that extended across a large range of angles.
I also rechecked my polarization and I'm sure I'm P-polarized, so that can't be the problem
I also need to prepare to give a chalkboard talk tomorrow in front of the other fellows and professors. This was in preparation for the LTC tour we're going to give on Thursday, which the other Simons fellows will attend.
Monday, August 9th
I attempted to get another film done today, but I wasn't able to talk to Mr. Davis early enough. Tomorrow I will ask Mr. Davis to make an approximately 600 nanometer film on the hypotenuse face of my triangular prism.
I did some of the math on ATR with my professor, and oddly enough we got an answer different than the one that my brother gave me. Instead of the maximum loss in reflectance occurring a couple degrees away from the critical angle, we found that it should occur some 21 degrees out. I examined that area, but still could not find the dip. I was unable to understand why I am not seeing it!
This week I decided to test some basic properties of the materials I am using, such as the loss in intensity after reflecting of the side of a prism. Based on Fresnel equations, it should be approximately 4% which it is. Also, the power of the laser is much smaller than it says it should be. This may be due to the laser's age. (1994)
Friday, August 6th
My abstract is due Monday. I spent much of today working on the abstract and the poster. I also did some additional research. I was able to find more articles on ATR, but nothing indicates that I'm doing anything wrong. I want to try the Otto setup now, because Dominic said something about matching wavevectors and how their easier to couple in the Otto setup. If I can get it to work with the other setup, I'll return to the Otto setup later. I've heard about the possibility of amplifying the evanescent wave using surface plasmon, which I could profile using the same wedge technique as FTIR.
My brother assisted me with some of the math. I found a couple of equations in a paper on the web and in Dominic's thesis that enabled the calculation of the distance required. However, I'm not sure if the equations are different for the Otto and Kretschmann setups, if you can just replace the variable for film thickness with gap distance. It has to do with how the evanescent wave propagates through the metal. The numbers he got were approximately 400 nm out and 1600 nm out for the Otto setup.
I was going to attempt to obtain another film, but I was unable to talk to Mr. Davis. This will have to be done tomorrow.
Thursday, August 5th
Today, I tried to learn more about half wave plates and their fundamental properties. Most materials have differing refractive indices depending on the frequency of light passed through them. However, there are also some materials which have differing refractive indices depending on the polarization of light. This causes one polarization of light to be delayed and be out of phase with the other one. Using this technique, it is actually possible to change the polarization of light 90 degrees. This involves shining the light at a 45 degree angle to the polarization planes of the half wave plate, and then having one phase shifted so that it is the reverse of what it was before. A clearer diagram is description and diagram in my scientific notebook.
I also heard of someone called Dominic today who Dr. Noe met at some meeting. Dr. Noe learned that Dominic spent a year working with ATR and surface plasmons for his thesis. This is wonderful news! He may be a resource to help me with my project. He came a couple of hours later, and he gave me a copy of his thesis to read. He wa short on time and therefore unable to examine my apparatus.
In his thesis, he seemed to have used the Kretschsmann setup, not the Otto setup (making the gold film directly on the prism, and creating plasmons on the metal-air interface on the other side.) He also used a much more powerful ~800 nanometer wavelength laser, and a 400 angstrom film.
Wednesday, August 4th
I started working on my project paper, trying to base it off in the same organizational sense as the ones that the REU students wrote, and my previous abstracts. Choice of words is extremely important in writing abstracts and some things you can say in the lab, you cannot say in an abstract, e.g. my laser hit a mirror and bounced into a photodetector (should be laser light, not laser). The royal we is allowed, but no other first person. The thrid person rules supreme!
I took some data on FTIR, attempting to get the largest range possible. I was able to get around four orders of magnitude before I discovered that my signal was flatlining. It was difficult to determine exactly where this was occuring. Because I'm scanning across a large range of values, it was difficult to find an area free of aberrations. Furthermore, scratches or pieces of dust located near the wider parts of the graph tend to mess up the curve more, since the relative change in intensity can be an order of magnitude higher
Tuesday, August 3rd
Because I wanted to make the film on my prism thicker, I went to Mr. Davis' office. We went together to Dr. Metcalf's office and asked him a few questions. He suggested I attempt to take data on the transmitted light, even though the frosted glass. He told me I should find the transparence of the film, by comparing the light scattering/ transmittance from a setup that includes gold and one that does not.
Today, I had to go to the 4 hour REU presentation session and listen to people's projects so I wasn't able to get any films done. The talks were interesting, though many were above my level of unerstanding. However, I was able to understand many of the talks from my cofellows at the LTC.
I went to Metcalf's lab to attempt to clean the unidentified containments off my prisms. This time, I cleaned them using a magnifier and acetone. Because the acetone does not leave a clean residue when it evaporates, I would then clean it with methanol. I believe I have cleaned the prisms to the best of my ability. The graduate students who work there told me more about the more advanced optics on the optical benches.
Tomorrow I will try either coating half or removing the coating for half my ATR setup, so I can gather data on both at the same time. I may be able to get another prism coated as well.
Monday, August 2nd
Mr. Davis sent me an email telling me that he finished the evaporating. It turned out badly due to containments on the surface of the flat. Even though the prism was straight from the package, there was still sticky stuff on its smooth face. I went through the other three flats and chose the cleanest one. I cleaned it, and gave it to Mr. Davis to film again.
He was incredibly supportive and showed me how the machine was set up. I've got several pictures of the machine and the components of it that cause it to work. One of the things I learned that I didn't before is that, after the vacuum is near complete, current is passed through a tungsten container, which evaporates the gold at near 1000 degrees.
Andrjez is back, so I went to his lab for a while to get some shim stock rolled. He has amazing skills at doing it,since the consistency is superb. I then went to Metcalf's lab to the flow hood to put the parts together. The assembly was successful, and I returned to my lab and set up an experiment.
My results so far are inconclusive. It seems I'm simply getting evanescent wave FTIR phenomenon. Also, I'm using the lens to refract the parallel rays of light produced by translating my prism onto the photodiode, which is producing multiple reflections that are messy. I will try a thicker film tomorrow(the one I am using right now is 308 angstroms thick) that isn't partially transparent.
Friday, July 29th
Andrzej came back today, but I already got help from Mr. Davis. I visited Metcalf's lab with Marty and looked into the laminar flow hood. Basically it's a small area partitioned with plastic curtains. It pumped filtered air from the ceiling down into the area. Unfortunately there was a lot of equipment lying around and it was too dirty. I might have to work in a more enclosed area, like a gloved filtered box.
I found an unused box that used to contain some lens or something else. I removed the existing Styrofoam from it. I then used an air duster and sprayed into the box with the cap half closed, to fill it with clean air. I'm planning to transfer the gold film mirror into the container, take it to the laminar flow hood, assemble the prism/wedge/foil setup then, and then bring the setup to the LTC for experimentation.
Further additions to my current setup included a diaphragm iris near the prism and a removable paper tube to cut out ambient light. Using this approach, when my laser is off, I get 0.00 mV of intensity reading. Also, with the help of Dr. Noe, we were able to add an adjustable amplifier to increase the sensitivity of our experimental apparatus.
Thursday, July 28th
I began analysis of the previous days data. Finding the penetration depth has some ambiguity, because it is defined as a percentage of the original beam. Does this mean that we find the distance at which the intensity equals the original beam intensity or the maximum beam intensity? The maximum intensity is not likely to equal to the original laser intensity because of two reasons: (1.) absorption of the laser beam by the prism, and (2.) because the distance of the gap at its thinnest point is not necessarily 0 (especially because our laser isn't a point source)
I also got an email back from Mr. Davis, who I asked for help doing the thin film. H asked me to come by his office. After some collaboration with Dr. Metcafe, we decided on a 500 angstrom thick film. I went to the lab where they were going to do it.
First, the flat or the microscope slide is placed on the top of a cylinder. At the bottom of the cylinder is the gold sample that is being evaporated. Also placed in the vacuum chamber is a crystal that has a resonant frequency. By vibrating it throughout the whole process, some of the gold collects on the crystal causing it to vibrate more sluggishly. You enter in the density of gold, and it can tell you the volume and thus the thickness of the film used. The vacuuming takes place by first using an oil to pump the gas down to a certain pressure. After that, the pump doesn't work anymore because there will be a little bit a backflow, which might introduce contaminated air into the chamber. Instead, a diffusion pump takes over, where a liquid is heated and evaporated, then condenses in a liquid nitrogen cooled chamber, and then bring molecules in the air with it.
Today, we watched a movie about Bell's inequalities, which has to do with a quantum paradox. Basically, Bell's inequalities are simple statements about the probability of two events being greater than a third, because the probability of the three events can be calculated by separating them into other probabilities, and then you can see that no matter what, the inequality holds true. However, when applied to a specific thought experiment about the production of paired photons traveling in opposite directions, it yields a trigometric identity falsehood. A paradox emerges!
Wednesday, July 27th
I searched for but still could not find Andrjez.I got an email back from Rich saying that me might be back next week. I continued with my research about surface plasmons for a large part of the morning, and then went the weekly meeting.
We attended a lecture about frequency combs, a method where we determine the frequency of a beam of light to extreme levels of precision using Fourier Transforms. Basically, instead of doing continuous integrals, you can use discrete ones to build a wave spectrum that produces a spike at one frequency. Fourier analysis is an important mathematical tool.
I took some data on the evanescent wave at different angles. I will now calculate the penetration depth, the point where the wave decreases to(1/e), and to see how it correlates with angle.
Tuesday, July 26th
I took the last data set from the scanning experiments. I determined that my best data came from the second to last run. This run was able to avoid the scratch that occurred on the previous three data sets, but was better than the last one, which had multiple abnormalities throughout the graph. I'll be using this portion of the prism to do more stuff with.
Today we also gave a tour to visitors from high schools and other places. Later, we went to the annual Vortex Party, which included a bunch of talks about optical vortexes and similar subjects. We heard an alumni of the LTC center, Giovanni, introduce optical vortexes, then we heard David's talk about Gaussian modes, and ended with some high school students. We ended the talk with this masters student who described industrial applications and now has a great career working with lasers and optics.
I went to the library today and checked out books about Electricity and magnetism, and am hoping to go over one of the sections about EM waves in conductors with Dr. Noe or Marty. Dr. Noe also mentioned a setup involving a chopper and a lock-in amplifier that greatly suppress ambient noise, so we can detect the evanescent wave in larger and larger intervals.
I still haven't obtained the metal that I want to work with. I have emailed Richard, who hopefully will know when Andrzej will come back.
I think I know the answer to the Gaussian distribution problem. Amazingly, the Gaussian curve thing doesn't affect the exponential component of the data at all. This is easily derived by going backwards: construct a graph that is exponentially distributed, take any average about an interval around x, and the end result is simply a shifted exponential.
I believe I finally understand how to use my setup as a Fabry-Perot interferometer to determine the wedge consistency. I've taken two data sets of the setup consisting of some 200 data points. The setup looks little like the images on Wikipedia and on Dennis' page.
Monday, July 25
On Friday, I attempted to find the angle at which the laser would fire perpendicular to the optical axis. I discovered that my rotational plate was not flat, so I took it apart and added spring washers to two out of three of the posts. This allows me to change the tilt of the table to make it flat. Now I can adjust both my laser and my rotational slide, and I started my data collection.
My first data set had a very noticeable hump 1750 nanometers. Because this abnormality was in a different place than the other abnormality in my last graph, it supported my hypothesis that these aberrations are simply prism incongruities or pieces of dust in the glass-air-glass wedge. I started taking data when my micrometer screw was reading 1.5, went down by 0.025 intervals until I saw a noticeable change (usually at 1.075-1.070) in intensity and then started to go down by 0.005 intervals.
I took 4 data sets so far, and interestingly enough the abnormality that can been seen in the first graph moves farther and farther towards the larger separation distances at a rate of approximately 500 nanometers per 3 mm vertical displacement. The data can be explained by a tiny diagonal scratch.
Friday, July 22
Today, Dr. Noe and I discussed my project more in detail. I still need to take additional data in a variety of ways, which is listed on my projects page. I began by completing some of notes of the previous page of the setup such as the circuit diagram, ray tracing, etc. I also did some calculations of the translation distance to gap distance transformation.
I now realize that I will be doing things here by myself when Marty and Dr. Noe aren't around. I still have many things to do with evanescent waves and FTIR. I'll work on ATR when they are around.
To do list: 7/22
I need to mount laser on a setup that allows for horizontal adjustment and angling. I will use this to scan prism face at different heights to see if discontinuity on the evanescent wave graph is due to the prism face or because of some other global phenomena. If possible,I need to find which level has the cleanest evanescent wave and use that level to find the critical angle.
I need to find the critical angle by graphing the evanescent wave at different thetas. I'll use this is calculate critical angle.
I need to do a transformation on the data collected to estimate the evanescent wave profile.
I need to find out how Fabry-Perot etalons reate to this project. I need to consider using them to discuss general trends along wedge surface.
I need to get optical flats coated and to use a clean room to do the ATR experiment.
I will be using xfig to draw my diagrams. It is an Linux application, but there is a windows version written on Java, which I use.
I didn't take any data today. I decided that it would be better to really think my experimental procedure through completely before cranking out a bunch of experimental data.
I need to remember for future data taking to also estimate the uncertainty, especially with voltage measurements or amplified measurements, since those tend to vary considerably. After taking the exponential factor into account, the lower parts of the evanescent field may just be noise.
I need to determine the beam width of my laser because it probably has a dampening effect on the evanescent wave. If the laser beam was a point source the evanescent profile would be just fine. However, it is actually a distribution of light and the photodiode is a couple millimeters in size. This means that I'm actually taking the average over an area.
Dr. Noe also mentioned that I should be careful of having my laser aligned horizontally when I'm moving it up or down. I think there will be problems, since the translation slide isn't parallel to the ground, so I'm going to have to find another way to scan consistently.
Thursday, July 21
I tried troubleshooting reasons why my setup isn't working. I rechecked the polarization, tried with a variety of angles near the critical angle, etc. I should be able to get a fairly decent evanescent wave profile. I am not, and I don't know why. I got a new power meter, and even used the lens to focus the secondary reflections onto the photodiode. Multiple reflections off the short faces of the prisms cause a series of dots that merge into a line.
I put the rotator slide on a relatively low angle so that some light came out. I took data on the light emitted. I took 40 data points at every 125 micrometers over a period of 5 millimeters, which gave me a very strange graph with multiple peaks and dips. It seemed to oscillate on the period of 1/4th of the translation distance measured with linearly increasing amplitude. I think this appears to be a the effect of a Fabry-Perot etalon, although it looks nowhere like what it should look like if it was purely a Fabry-Perot setup.
After being frustrated for many hours, I decided to switch out the prisms to the two new ones (we bought four) and soon I saw a tiny pale dot appearing at the thin end of the prisms. It seems the cleanliness of the prisms necessary is of paramount importance, since even the smallest amount of dust can cause the gap to be too large. I unwrapped the prisms halfway, and as quickly as I could, used a piece of lens paper to clean them simultaneously and push them together. Success!
One problem was that the beam was faint enough that running a power meter connected to the photodiode on milliamps still resulted in data not precise enough for my liking. Lauren assisted me and taught me how to read resistor's numbers, and how to use a power meter correctly. Thanks Lauren! I added a 100k resistor in a parallel circuit and measured the voltage instead of the current, which gave me much better results. Success!
I then added a roll of paper around the photo detector to isolate the laser beam from ambient light, turned off all the lights in the LTC center, and started taking data points with a flashlight. After taking some data in first 25 1000th of an inch, and then 5 1000th of inch when it more interesting, i was able to construct quite a neat graph that showed quite clearly the exponential nature of the evanescent field, with a r^2 value of .9913.
I need to remember to ask Dr. Noe about a review article he mentioned to me.
Wednesday, July 20
I spent the morning unwrapping my new optical prisms and mirrors. They were hard to extract, but once I took all of my stuff out, I placed it in a tray and got a label with my name on it. I then used the prisms and a new piece of shim stock to construct the FTIR setup.
I heard a lecture from Laser Sam Guru who came today. He talked a lot about laser stabilization using a Fabry-Perot scanning interferometer. By using a piezoelectric driver, you can oscillate one of the partially reflective mirrors to find the distance at which there is near 100% transmittance, which is an integer multiple of the wavelength.
I attempted to attain readings from the experimenal apparatus, but for some reason, the distance on the wedge did not change the intensity of the emitted wave. Afterwards, we attempted to find a better shim stock. We went to a different lab and I asked Rick if he would roll as piece of our shim stock down to 0.0005 inches, which he tried. He had difficulty doing this. So we went back to the machine shop and got a 0.001 copper shim stock for him to roll down. The end product was thin enough, even though there were deformities on the edges of the film. I cut the excess and used it.
The prisms seem very flat. Interference fringes are just about as good as the optical flats against each other. However, I'm not able to find the point with 100% transmittance. I even tried adding extra rubber bands, and it's not improving. I'm getting almost no light to come in on the wide side of the wedge, and then moving it to the pointy side of wedge to see if there are any changes in intensity. I'll now calculate the critical angle in a different way to see if I can get a reasonable answer. I wonder if my prisms are squishing my wedge so that it is no longer wedge-like.
I got invited to dinner with Dr. Noe, Marty, and Sam! It was my first time in an Italian restaurant. We talked about scientific stuff the whole time. How come I can't find any friends like this?!
Monday, July 18th
I explored the citations at the end of an article on optical modulators and found several ones for further study. The Wikipedia articles about plasmons, surface plasmons, and surface plasmon polaritons offer some interesting sources. There are a narrow field of authors that are considered the founders of the discipline. I've got around eight articles now that I can possibly use in my project research binder. Most of these I don't fully understand at this time. I am hoping to gain enough information to write my introduction soon.
As for recent research, there seems to be a surplus of articles originating in the past few years. I doubt interest in this field actually surfaced this late though. It's more likely this is due to the search engine I used.
Dr. Noe sent me an email saying that a delivery arrived for him, but it turned out to be the battery for his camera. Disappoinment since I was expecting a component. I was hoping on starting my expeimental setup today. There is always tommorrow!.
I found out was that surface roughness (with grain size of less than the wavelength of light used) has effects on the induced plasmon resonance. However, this effect effects the optical modulator insignificantly. The equations are still sort of confusing to me, but I think they are describing how the plasmon resonance vector will change or shift.
Friday, July 15h
The two main questions I want to answer are: (1.) how does the coupling between photons and surface plasmons work; and (2.) if it is a strict relationship or not. I've heard that if you want to use photons to excite plasmons, you need to make sure that their impulses match. I was worried that if I didn't use the correct wavelength of light, then the plasmons would not interact with the evanescent wave at all. However, it seems that, because it's the evanescent wave that interacts with the plasmons and not the photons themselves, any wavelength light can work, it will just change the energy profile of the evanescent wave and the distance (which is the area where the coupling is the most efficient) at which total transmittance occurs is in a different place. The curve for the magnitude of the evanescent wave to excite plasmons is therefore the graph of reflectance over distance.
I did some research on K-waves, which were supposed to be the variable that has the greatest effect on surface plasmon coupling in attenuated total reflectance. I wrote about this in my scientific journal. I still need to go through elected references in the main article to learn more. I need to learn how to use a drawing machine, so I can draw nice diagrams.
I talked with Dr. Noe today and we chose a prism and an optical flat to purchase. Last year, Dennis' prisms came within a day so I'm hoping for the same.
Thursday, July 14th
Today I mostly did research on the theoretical aspect of my project. I'm still waiting for my parts, which Dr. Noe ordered today.
I also improved my laser safety skills. This is very important! Now, the excess beams created through multiple refractions/reflections do not go to other side of the room. I adjusted my experimental apparatus so that no laser beams were free to land on the other side of the room.
I uploaded my project page. I took the time to take pictures of my experimental apparatus and the lab although I don't think I'm going to upload all of them because of the storage size constraint. There's also a description of my current experimental apparatus and its evolution. I will be allocating some of the stuff I normally right in my journal into my project page from now on, which is why my journal entries are likely going to be shorter.
Wednesday, July 13th
I also attempted to experimentally determine if the ATR effect exists. I set up the prism at the correct critical angle and when I moved the transition slide so it approached the sharp part of the wedge, I saw a faint red dot exiting from the back of the mirror. I was still skeptical of the setup. When Marty examined the setup he said that it was likely due to a malformity in the prism or a partial reflectance on the exiting side of the prism (because the mirror does not cover the edges of the prism). Marty gave me an interesting question to consider.
He wanted me to estimate the approximate boundaries in which the reflectance would decrease and compare it to the beam of the laser. Basically, the edge of the prism is 30 millimeters long, and the thick part of the wedge is 38 micrometers (.0015 inch). Because the minimum of the ATR reflectance graph occurs at 1000nm or 1 micrometer, you divide 30 millimeters by the ratio of the needed wedge thickness to get a little less than one millimeter. This is also the approximate thickness of the laser beam. Although we have a micrometer that we can use to change the location of the laser beam relative to the wedge, the thickness of the beam will prevent there to be complete transmittance.
We had a lunch meeting today, where we discussed the progress of our projects. I talked about my project and explained it to people, and got some feedback. The professors believe that this project is feasible, but it may be difficult, so in case the FTIR portion of my experiment fail, I can still write a report on FTIR.
I did additional research to find better prisms and mirrors. One of the things that you need to know is the smoothness of the prism. The main method in assessing if something is smooth enough is a fraction wavelength. This is displayed in the form of lambda/n, where n is usually 4, 10, 20, 60, or 100. These are approximate measurements, where anything about n=4 is not considered a precision lens/prism/mirror. I need at least wavelength/4 smoothness to have a representative air wedge.
I also needed a smooth coating, but I discovered that I probably can't do it with the mirrors we have in the lab.The mirrors we currently have have a protective coating made of an oxidized metal. This is likely to prevent the surface plasmon resonance phenomenon from occurring. I'm planning to buy an optical flat and ask someone from a different lab to make a gold plating.
Tuesday, July 12th
Today, I was able to secure the plated mirror to the prism using rubber bands. I found a small clamp that I could use to secure the prisms to the table.
I took time to write in my scientific journal the current setup. I will include additional diagrams on my ideas page. I also thought more about the method in which I would detect the intensity of light. I decided that I would mount a lens with that focused incoming parallel beams of light into the light sensor on the same stand as the light sensor, and then move the light sensor wherever the reflected light would be (because the critical angle of my prism is not 45 %). Hopefully, this will allow me to move my prism without messing up the orientation of the beam relative to my photo detector
One of the things I was initially confused about was the appearance of multiple dots reflected onto the face of the laser, sometimes up to three of four. I realized that they existed because the light would reflect off the 2 legs of the triangle of the prism, bouncing back and forth and releasing some of the light out the front entering face back at the prism. While in the beginning, this made the calibration of the apparatus difficult, I soon discovered that the first reflection was the leftmost one.
I drew a couple of diagrams and did some math today. To determine the critical angle, you simply have to first position the prism so that the beam of light hitting directly at the first plane of the prism bounces back into the laser, and then turn the turntable until you get you just barely get a critical angle. Record the difference in the angles (up to 6 minutes or 1/10 of a degree) and then add the angle of the triangle of the prism. By first doing this when the film/other prism is removed, you can then add the film/other prism, replace it on the rotation slide in any orientation you want, and repeat. This way, you do not have to make sure you're prism is located at the 0 - 180 line of the turntable every time.
Marty discussed with the project with me. He mentioned that it was possible that my prism and mirror were not smooth enough that the thin part of the wedge was under one micron. He noticed I was using a piece of paper as a wedge material and took me to the machine shop to look for a more specific thickness material. We found what seemed to be a sheet of rolled brass that was exactly 15 microns thick, I used it to replace the paper wedge. Success!
I read in the article that I needed to polarize my laser, so I attempted to do so. However, I found that my laser had a built in Brewster window, which caused only light polarized in a certain way out. However, my laser was oriented incorrectly, so I realigned it.
Friday, July 8th
I began the day with some research about ATR, specifically surface plasmon resonance. It is the topic I'm least knowledgeable about since it is concerning some quantum optics. In any case, I explored the relationship between plasmons and attenuated total reflectance. I found that surface plasmon interaction should occur with any film of dielectric material with a constant opposite that of the intermediate medium. This means I should be able to do it with aluminum foil, although I did find a silvered mirror later.
For the hands-on portion of my day, I changed the sides of my laser so its pointing towards the wall, and added 2 micrometer screw bases, which took a long time to attach since the screw connections were of a different size and type from the ones on most objects in the lab. I also learned where most of the mechanical attachments were located in the lab. I also found a relatively flat (although it does have many scratches) silver plated first surface mirror to use for the ATR portion of my experiment.
I found a new prism to play with (a 45 right prism) which has an index of refraction large enough so that TIR occurs when a non-hypotenuse side of the triangle is oriented perpendicular to the last beam. Using the micrometer screw, I was able to test the one dimensional distribution of the laser beam, which was approximately Gaussian. I also calculated the x-displacement of the photo detector to compensate for the y-displacement of the horizontal slider.
I'm looking forward to being able to compare the results of the transmittance between FTIR and ATR. I still haven't been able to show that the gap is small enough because I don't know where the high quality prisms that Dennis used last year are located. I'll need to talk to Dr. Noe later, I thought he would be here today, but he didn't appear. :(
Thursday, July 7th
In the morning, I researched some articles that were of use. I reviewed some of the things I learned in the two previous lectures and I transferred some of the notes to my scientific journal.
Today, I spent most of the time attempting to construct my experimental apparatus. The first thing I had to consider was what orientation I should position my components that would be the easiest. I considered having the laser point at an angle up towards a prism with one side parallel to the ground, a laser point up, and a laser pointing parallel to the surface of the optical table. I eventually settled on a slanted version.
There are several criteria that needed to be met for my experimental apparatus to work. I needed a way to control the distance between the prism and metal film. I also needed a way to set and control the angle of the light so that it hit the prism inside surface at near the critical angle. With these two things in mind, I decided to place the metal film at an angle to the prism, so it can be easier to control. However, there could be problems with aligning the receiving sensor, as deviations from the center of the beam could be mistaken for losses in intensity due to ATR.
Carrie helped me around the lab, showing me where possibly helpful objects were located. Thanks Carrie!
Wednesday, July 6th
I found the a translation plate and a rotation plate, which I'm planning to use in either Dennis' FTIR project or the new ATR project. I'm also trying to get more experience setting up optical mechanics. I observed and assisted Carrie construct a device to test the index of refraction for a collection of prisms.
I think my course of action for the next few days is going to be constructing the apparatus for one of the experiments by Friday, or at least until I find that I'm missing a critical part or device. I'm going to attempt to see if some of ideas are plausible before allocating too much effort in the wrong direction.
I asked Marty about testing the smoothness of prisms. The first thing I learned was how to properly clean and utilize prisms. We used a special solution that consisted of a fast evaporating alcohol-based solution applied to a lens cloth. I fished around in the "prisms" box to find two right angle prisms I could play with, and then found the flat plate used to test for smoothness. Basically, one face of the block is used as a control or basis to define a flat and smooth surface. By placing other supposedly flat planes on the block, you can determine how good a match it is. Multicolored interference fringes can be seen by looking through the prism; the wider the bands, the better match, where the bands curl around the point of contact. Because we used a right angle prism, looking through the prism from an angle will allow us to assess whether optical bonding would occur. However, optical bonding rarely occurs without the introduction of a film of fluid or some other intermediate medium.
Tuesday, July 5th
Today, I read about and defined several types of rays, because I'm trying to learn more about optical modes and ray types. They are coming up in different articles. I still don't understand how an leaky mode dissipates energy through cladding. I originally assumed that the mode was simply a mode in the optic fiber that's at an angle that is below the critical angle. However, it is close enough to propagate properly. From more reading it seems more complicated.
I added additional notes on the types of modes in my scientific journal.
I also spent some time reading Dennis' article on demonstration of FTIR using a transverse micrometer and a turntable. His experiment was able to verify the exponentially decaying intensity nature of the evanescent wave. He utilized a wedge shaped air gap to carefully control the gap distance. However, more interesting than measurement and validation of the evanescent wave was his experiments with the Fabry-Perot etalon. The diagram for this mechanism looks different from the type that he used, but the effects are conceptually equivalent.
A Fabry-Perot etalon is a interferometer that bounces a ray of light between internally between two mirrors or the inside of a prism. when the angle is sufficiently small, the rays of light overlap and due to different path lengths they either constructively or negatively interfere, leading to periodically interference patterns. Dennis did not mention how his interferometer worked.
Dr. Noe gave me the question as to why the peaks on his graph was so spikey. I found a similar graph on the Wikipedia which shows different graphs, some more spiked than others. The more spiked one was labeled to be the one that had a higher mirror reflectivity. On Dennis' website, the graphs were vastly different for horizontally and vertically polarized light. I believe this is because the reflectivity of the prisms are different based on the polarization of the light reflecting.
Saturday, July 2nd
I will still make journal entries on the weekends.
I'm trying to develop ideas that aren't related to near-field phenomena. I'm considering doing a project on a prism polarizer. Basically, if something has bifringence, differently polarized light interact differently with the material. This can cause a prism made out of a bifringent material to separate polarized light, and if done at the right angle, have one of the rays of polarized be trapped in the waveguide, while the other escapes.
There's a magazine, "Applied Optics", that is supposed to be a good source for project ideas. I'll read it.
Going back to my project about FTIR, even if I use the same setup, there still are things that I can do if I have a different Research Question. Maybe I can change the wavelength or polarization of light used as well?
There's another idea using attenuated total internal reflection. (Small fast large-aperture light modulator using attenuated total reflection, Sincerbox and Gordon)
Blazed gratings are a type of grating that has a type of saw tooth pattern that works the best with a certain wavelength of light. It has applications in planet-finding astronomy.
Friday, July 1st
We discussed was what project should I start on. He mentioned Dennis' work as a start for my project. The idea is, I should duplicated his work, and then maybe I could explore by placing materials in the tunneled gap, or things like that. I could also explore some of the "sharp peaks" of the graph.
Dr. Noe says that I need to keep in mind is that he mentioned that a very complicated and applicable project is not necessary to do well in competitions. All one needs is to demonstrate the effect, and have a "scholarly attitude": being able to discuss knowledgably about information in the field in an up to date way.
I also looked briefly into LIGO, which is somewhat analogous to an interferometer setup that Dr. Noe mentioned a couple days ago. Apparently, the people there have to account for vibrations of weather in Japan.
I've also thought more about the plausibility of some of my previous ideas. I don't see when the optical cable interference idea would be needed to be applied, since it would only occur if there is a cladding and mechanical barrier that are around the same size as the wavelength of light, and the optic companies likely make them specifically so they don't. I'm still attempting to search for an exception. The whispering gallery thing also seems extremely hard to get coherent data from.
Thursday, June 30th
I decided to do some research on polarized light, a topic that I've never really learned about in my school or through my projects, but can't be ignored because of its occurrence in so many optic problems. I'm using the book "Introduction to Modern Optics," by Grant R. Fowles. I'm seeing if I can brush up on my Maxwell Equations as well. I'll make some notes in my scientific journal.
I'm still looking for ideas for my project, I want to get maybe three more ideas considered today, then, I can ask Dr. Noe about which ideas I should develop further. Maybe I can write a project proposal on Friday.
I'm getting a lot of good results just by searching "evanescent wave" which seems to be a very popular keyword in FTIR and FTIR imaging related journals. The great thing about is I don't have to go to the library, I can have it send the stuff in html format to my email for me to read at my leisure! I still need to make sure that the project can be accomplished with my available equipment in the available time.
Plasmons are coming up a lot. I looked on the wikipedia and the explanation isn't too clear. Ill need to dig deeper!
I had some practice fixing a simple mirror onto the optical table. The controls for manipulating the mirror are much simpler than I thought; it's really just one knob is for vertical movement, and the other is for horizontal movement. Carrie also put me up to the task of determining the amount of deviation of the laser per amount turn of the knob. This information will probably turn out to be useful in the future if I ever need to know how much sensitivity I can put into an optical table. (arctan(amount_moved/distance) / #_of_turns) = (arctan(4.2cm/100cm)/5 ), approximately .04 degrees per one rotation of the knob.
I think I'll spend part of this journal entry explaining Maxwell's equations.
Gauss's law: States that electric flux is proportional to the amount of charge enclosed in a surface;
Gauss's law for magnetism: no magnetic monopoles;
Maxwell-Faraday: electric fields are produced by changing magnetic fields; and
Ampere's circuital law: magnetic fields caused by changing electric field or current.
Something to consider: I don't want to just repeat someone else's experiment. I can do that first, and then attempt to try out some ideas with the setup, but I want to either develop an innovative experimental setup, or apply it to a new thing, and make is specialized for that subject. Optical near-field spectrometry has been applied to cancer and pathologic too many times. Besides, I don't have the equipment for that kind of thing, and I don' think I could contribute to the field. I probably will have trouble getting my hands on anything bio related.
Also, Carrie showed me an article about a evanescent wave coupled "whispering gallery" that she found while searching for her frequency doubling project. http://metrology.hut.fi/courses/s108-j/Nano2.pdf . From what I can tell, light is stuck inside a droplet, and flies around inside the droplet in a ring. I don't quite understand the connection that this has to an actual whispering gallery, but people use evanescent waves to pump energy into the waveguide. It has applications is microlasers and microdetectors.
David and I got into a discussion about evanescent fields. I was pretty sure that, although they carried energy, the creation of evanescent fields would not cause the total internal reflecting light to loose energy, as long as there was not anything coupling with the light. It turns out that evanescent fields do consist of energy, but return it to the laser (unless impeded by a particle or transfer medium).
Wednesday, June 29th
I am searching for interesting articles I can use as a start for my project. I want to start doing something as soon as possible, maybe even get a project proposal Friday. I'm using the search engines on the American Journal of Physics website, as well as the more broad database search for the libraries at Stonybrook.
In particular, I'm looking for a certain experiment that I remember reading about when I was doing research for my FTIR project. Due to the proximity of optical fibers in an optical cable, and the fact that optical fibers are emitting evanescent waves in all directions, even if sufficient cladding was placed between the optical fibers, there might possibly be the coupling of the various optical fibers. I'm wondering how to test this, as there are no square optic fibers, so the area for possible evanescent wave transmission will be a line where the two optic fibers touch. The advantage of attempting to test for FTIR through waveguides like this is that evanescent waves are produced along the entire waveguide, allowing for possibly better transmission. However, this also makes controlling how close the optical fibers are a challenge, as it would be easy to space out the mediums too far away, or too close so they optically bond and couple through conventional means. Wikipedia explicitly mentions single-mode fibers to be have this effect, but mention most of the evanescent wave is carried in the cladding.
Perhaps this is a dead end, but I'll look into it anyway.
I'm learning more about what exactly is modes in an optical fiber via exploration in boundary conditions, Maxwell's equations, Helmholtz equations, and other topics. I looked up the sizes of single mode optical fibersWe also had a meeting with Dr. Metcalf, Dr. Noe, and Dr. Cohen. I presented my FTIR project and Metcalf gave me some things to think about. He asked me if I've ever heard of the setup where someone places an absorbing material in the path of the evanescent field. I said yes. He asked what is the smallest amount that is able to produce a noticeable difference in intensity, which turns about to be a single atom. Using this technique, scientists can keep track of individual molecules, cells, and even interactions, such as chemical reactions, viral infection, based on the frequencies of light emitted.
Tuesday, June 28th
The walk from Mendelsohn quad to here is around eight minutes, and when I got here, I decided to go check out the library on Floor C. It turns out my ID card I got yesterday wasn't put into the library system yet, so I can't check out books yet. I'll go to the Main Library (3rd level) later in the day, if I have time. Note to self: LTC door opens into the room, not out.
For the Sun problem, the image if the sun on the sun would be just as big as the sun. This is due to the fact that the mirror (0.1 meters) is so much smaller than the sun ( 1.4 * 10^9 meters), that the mirror acts sort of like a mirror with a pinhole paper pasted on it.
I learned some Linux and some Vi ( a text editing program) that I use to maintain my journal and website. Right now I'm really slow, but I think it will get better in time. Perhaps if I use Notepad++ as my text editor instead.
I learned more about what other people are doing, about beam splitters, our options here in the lab, about HG and LG modes, and about certain useful optical setups that involve these effects, mainly what other people are doing. I'll try to be more specific in the future about specific things I learned.
I participated in a discussion on the interferometer. Basically, using a rubber band to pull back one of the mirrors a minute amount (approximately one micron per second) the difference in path lengths would cause the interference pattern to shift to the side. This can be thought of as a transitive effect from one scenario with an interference caused by a path difference, and another scenario with an interference caused by a path difference. However, and interesting way to look at it is via the Doppler shift. Even though the change in distance is extremely small, the difference in wavelength need only be near nanometer scale to have an effect.
An interesting follow up mini-experiment was done by pulling back two mirrors that worked no different paths after the beam splitter. When both are pulled at the same rate in the same direction, there was almost no difference in interference pattern whatsoever. When pulled in different directions, the speed approximately doubled. There was some initial confusion with this result, as after pulling a certain amount without continuing increasing force, the speed will drop and halt. However, this would not occur if the movement of the rod was constant.
Monday, June 27th
The plan for today is to go to the informal meeting and meet other Simons students, then get ID cards, and go to breakfast with professors and parents. It is nice of Simons to provide us breakfast. ID cards will be very useful too, they can be used everywhere, even in the laundry room.
We went to the Simons meeting today, sat down, ate breakfast, and then was given our ID cards. Dr. Noe came by to pick me up.
I looked around at what the students were doing. I saw the start of a dye laser, someone manipulating an optical vortex, and an interesting setup to get a laser into a single mode optical fiber. It was kind of overwhelming!
Several books for background study were recommended to me: "Feynman lectures" (v1), "Elementary Wave Optics," and some new book that I didn't manage to get the title of.
When the Sun came out we went out and played with a Fresnel (the S is silent) lens and burned some stuff. I already read the journals of other students, so I know why a focused magnifying glass does not produce a point, it produces an image of the sun. However, Dr. Noe gave me another problem, which was, if I had a flat mirror and projected an image of the sun on the sun, how big it would be? I'll draw a ray diagram later.
I was thinking of my subject for my project, and decided I was interested in fiber optics. I'll be looking through those later.
I will have to figure out how to use Linux later.
Sunday, June 26th
Today, we got here a bout 11:00 AM on Sunday and the program starts on Monday. I got situated in my room with my roommate (we're both from the same school). Everyone is pretty nice.
I noticed the buildings here are really good. The campus is very new. For instance, the Simons Center for Geometry and Physics looks very modern, includes an evaporative fountain cooling system, bio-roofs, glass window walls, and an kinetic museum inside.
The physics building basement is where the Laser Teaching Lab is located, just through the main doors down a flight of red stairs.