Research Journal

April 29, 2015

Today was the URECA event! Since this was my first time not only presenting, but also attending the event I was very excited to be a part of it. Presenting my project to students and professors was a learning experience. It felt more like a conversation with the person rather than a formal presentation. I was surprised to hear that many people were not familiar with this topic so I had to explain all the background information before I explained the more detailed parts of my project. Presenting the project also helped me learn more about the topic. When someone asked me how one would determine the internal structure of the moon just by using the three Apollo retro reflectors, I had to think about it before I answered. I told them that one way would be to measure the distance between each retro reflector and Earth (this can be done using the time it takes for the laser pulses to return to the detector) at a certain time of the year. Then this will be repeated about 6 months to a year later. The times will be compared(this is so that the Moon's shift in axis and thus the entire Moon's distance to the Earth does not have to be taken into account). If one of the retro reflectors took longer compared to the rest of the retro reflectors, this means that there was a shift in the Moon's crust.

During URECA I also had the chance to look at and learn about other student's projects. I really liked how there was such a variety of projects on display. One of the projets that stood out for me was a geology one where the presentor talked about how she was able to measure the shift of the Earth's crust, specifically in California after an earthquake, using GPS satellites. This sounded pretty similar to what the retro reflectors on the moon can do.

Overall, my experience at URECA was a great one, I hope to participate in it again during my upcoming years at Stony.

April 16, 2015

It was interesting to learn about Jasmine's and Rachel's projects as well. I wrote about birefringence in a previouse journal entry (February 26, 2015) so I did not have any trouble following along with Jasmine's project. For Rachel's project, however, I was a bit less familar with the material. It was interesting to hear about how she is going to do her research with this "red box" and that she needs to figure out not just what is happening but how and why as well.

After this meeting I realize that I still have a lot of work to do to prepare for URECA (which is in just two weeks!!). Making a "To Do" list will help me organize all of my thoughts:

To Do:

1. Put together poster for URECA
2. Create and work on my project's Report
3. Put together my Refrences page with a short description of each refrence.

April 14, 2015

Today I went into the LTC to collect some data for my project. I wanted to test the divergence of the laser before it reflected from the retro reflector and after it reflected from the retro reflector back to the laser pointer. I also wanted to measure how alligned the reflected laser image will be with the laser pointer.

My setup included: a cube retro reflector, a ladder to hold up the retroreflector, a laser with a diameter of a few mm (about 1-2), a piece of paper with a 3mm hole at the center (this is to to allow the laser pinter's beam through, but to show the reflected beam from the retro reflector).

I started by turning on the laser beam and aligning the retro reflector on the ladder so that the laser beam fell directly at the center where the three mirrors intersected with one another. I then took my blank piece of paper and placed it right in front of retro reflector and measured the laser beam at this point. This would tell me how much the laser beam divereges right before it hits the retro reflector. Then I let the laser beam hit the retro reflector and bounce back to it's original source (the laser pointer has a piece of paper, with a hole that allows the laser beam to get through, right in front of it). I had to adjust the retro reflectors several times until I was able to reflect the light back so that the hole for the laser pointer was in the middle of the hole made for the laser beam. When I was able to get an image nearly overlaping the laser beam, I measured the divergance and took photos of the result.

Some of the physical measurements that I took are:

1. Laser beam size from the laser pointer and to the retro reflector: 1.5 cm (min) and 4.5 cm (max)*
2. Laser beam size from the laser pointer to the retro reflector and back to the laser pointer: 3.0 cm (min) and 8.7 cm (max)*
3. Intensity of the laser beam: 1 mW
4. Distance from the laser pointer to the retro reflector: 10.2 m + 144 in = 13.8576 meters

April 09, 2015

Today I had a meeting with Dr. Noé and Jasmine. We went through a couple of the details for URECA event, such as when to help set up and when the presentations start. I also had the chance to hear a little more about Jasmine's project and share my project with her as well. For my project I decided to cut out the information about the cat's eye retro reflectors and focus on the lunar laser raging experiments and the challenges involving that.

I found a really helpful paper outlining some of the topic I want to include in my project. I also found the links to the NASA website for each Apollo mission that had retro reflectors on it: Apollo 11, Apollo 14, and Apollo 15. These last three links will help me learn more about the design of the experiments. I am also looking for more original papers of the actual built of the retro reflectors.

April 07, 2015

Today I meet with Dr. Noé and finalized a couple of ideas on my project. Instead of covering the cat's eye retro reflector, I will focus my project on the lunar retro reflectors. Dr. Noé liked my titles and suggested two more:

1. Optics of the Lunar Laser Ranging Experiment
2. The Lunar Ranging Experiments

Also here is a "To Do" list of items I need to finish:

1. Decide on a title
2. Submit form for participation in URECA
3. Edit abstract
4. Find and study the original papers on the lunar retro reflectors
5. Research the "diffraction limit" and apply it to my project
6. Start planning out poster

I started looking into the lunar ranging experiment original papers right after our meeting. Here is a link to one of them.

April 02, 2015

In preparation for today's class I researched different aspects of retro reflectors that I want to include in my project. I found out that there is a type of retro reflector called a "cat's eye" retro reflector, which allows for the surface to be curved. It is similar to other retro reflectors in that when the angle of the reflective material is changed by α the angle of the light is changed by 2α. In my research journal I added the background information about this retro reflector and showed how it works. Here is a sample figure of this: This image shows how even in a curved reflective surgace (such as in a Cat's eye retro reflector), light (of different incident angles) can be reflected back as parallel.

I also found out how to calculate the field of view of a mirror:

1. Draw a ray from the eye to one end of the mirror. This is the reflected ray.
2. Then in accordance with the law of reflection, draw the incident ray.
3. Repeat for the other end of the mirror.

By doing this, you will find the field of vision of the mirror.

At today's meeting Rachel Sampson visited and listened to all of our projects. She then gave us tips on our abstracts. Rachel S. also talked to us about her previous and current research. Hearing about it gave me ideas about how to improve my project. Additionally, Dr. Noé told us that it is important that we have a plan about each of our projects. He also said that for URECA it is important that we show understanding of our topic, even if it means not taking physical measurements. Therefore, after class today I made several plans and decided that my project will include the following:

Introduction:

-Background on retro reflectors

-Background on the Lunar/ Apollo retro reflectors

Show Understanding in the Following:

-How light travels to a retro reflector and bounces back parallel

-How if the angle of the retro reflector is changed by α then the angle of the returning light is 2α.

-How “Cat’s eye” retro reflectors work so that the light bounces back as parallel even if the surface is curved.

-How if the angle of the “Cat’s eye” retro reflector is changed by α then the angle of the returning light is 2α.

-How to determine the Field of View (FOV) of a retro reflector.

Conclude

-How are retro reflectors are important in every day life

-How to calculate distance to the moon using retro reflectors

Now I just need to find a way to incorporate all of this into an abstract.

March 26, 2015

During our meeting today we talked about our abstract deadline (April 8) and the URECA day (April 26). I am excited to start writing my abstract; I had to write one for previous research and I remember how it took many hours of hard work and numerous edits until I was able to submit a final copy. Dr. Noé informed us that we need to have an eye-catching title for our project. Since my project involves retro reflectors, and there are retro reflectors on the moon, I would try to incorporate that into my title. After class today, I worked on finding several different titles that I can later choose from. Here are three of my favorite titles from the list:

1. Shooting the Moon with a Laser: An Exploration of the Lunar Retro reflectors
2. Don’t Reach for the Moon, Shoot a Laser at It: The Optics of Retro Reflectors
3. Did Man Ever Set Foot on the Moon?: Proving Human Space Exploration Through the Lunar Retro Reflectors

The last one was inspired by a Mythbuster's video that Dr. Noé shared with me. In the video they proved how the “myth” that man has ever set foot on the moon is true and can be tested using the Apollo retro reflectors and a really big laser. Additionally, today in class I was able to show Jasmine and Rachel a simple retro reflector (one with just two mirrors at 90 degree angles to each other). When they looked at it, they said that they were unable to see what they had originally seen with Dr. Noé ’s smaller retro reflector. This made me wonder about the field of vision of a retro reflector and how I could possibly calculate it.

March 13, 2015

Today I met with Dr. Noé and talked more about my project. He explained that for URECA I could demonstrate the retro reflector and have a poster that shows calculations showing the exact path of the light as it travels to the retro reflector and back. I can also calculate that when the angle between the two mirrors of a retro reflector is moved by an angle, alpha, then the resulting angle of the laser beam is moved by two alpha. In addition to these calculations, I can also have a diagram showing where the Apollo retro reflectors are on the moon and how one could possibly shine a laser onto them. Dr. Noé sent me the link to some interesting websites with further information on retro reflectors. One of my favorites was one that had a comic, which would be a nice addition to my poster for URECA. Another website had information on something that we talked about during the first day at the LTC: how one would be able to measure the distance to the moon using retro reflectors. This is something that I would also like to include in my project as a calculation since it is what initially sparked my interest in retro reflectors.

March 12, 2015

With Dr. Noé's help, I spent this week deciding on my project. From the list I had before, I crossed out optical tweezers because a project involving that would be too long term. I also crossed out optical vortices because of how complicated this topic is and also because it's not well-suited to the audience at URECA. Therefore, I decided to make a project involving retroreflectors because I would be able to finish it in time and also demonstrate retroreflectors when I present my poster at URECA.

Retroreflectors are optical devices that return any incident light back in the direction from which it came. The concept of the design we are considering involves perpendicular mirrors arranged such as at the corner of a cube. If a laser is then aimed at the retroreflector, its light will bounce off each mirror in turn, with the net result being a precise 180° turn; this does not depend on what angle the light is incident on the device. The image below shows the principal of a retroreflector:

As one can see from the photo, the angle at which the laser is aimed at the retroreflector does not matter, but the angle of the retroreflector must be orthogonal. If this angle is not 90 degrees and deviates by α, then it will cause the return beam to deviate by 2α. As I have mentioned before, retroreflectors have been placed on the moon to make possible very precise measurements of the earth-moon distance. However, when shining a laser beam onto the moon's retroreflectors one needs to keep in mind that the laser beam will diverge. I read a previous student's research paper on how laser beams propagate. She explained how the light intensity distribution has the form of a Gaussian curve that gradually increases in width.

These are all ideas that I need to take into consideration when I am planning my project. Even if my distance is only going to be a couple of meters, rather than to the moon and back, I still need to take the laser beams divergence into consideration.

March 5, 2015

Due to the weather we did not have any class today, so we needed to email Dr. Noé our ideas for possible projects. I am interested in three topics:

1. Retro-reflectors
2. Optical tweezers
3. Optical vortices

Dr. Noé really liked the first idea because it would be possible to demonstrate retroreflectors at URECA.

In my new WISE 187 rotation (Engineering Design Innovation with Topology Optimization), we needed to design a project that involves a system that undergoes a change and model that topologically. I really liked learning about the how solids deform under stress so I decided to use this for the system. My project partner suggested that we use a bike frame as the model because this would allow us to test varying bike models. We both used the standard bike frame and then each had our own bike model. To create the system we first had to draw a 3D model of the design. Then we used a computer program to input all of the information about our model (such as its material, the amount of stress we want to put on it, if it has any fixed ends, etc.) and then allowed the computer to calculate how the solid changed. Here are my results:

The color spectrum shows that the areas that are more blue/ green in color are most affected (deformed) by the stress applied. I still need to analyze my results in more depth in the next couple of classes. It was nice to relate what I am learning in my WISE rotation to a topic that I initially was introduced to in this class.

February 26, 2015

In preparation for today's class I decided to research a few papers with topics that could become possible projects. I found a few concerning fiber optics and how to find a good material for the coating (outer part of the tube) that is cost efficient, but will also prevent any leakage. I also found that there are different materials used for the inside of the fiber tube as well, silica vs. soft glass, which have different indices. This led me to research if different colors vary from one another in cost. I found that they do, and that green lasers are the cheapest to manufacture. While these two topics were interesting, I dont believe that they would lead to a project.

Today in class we spent some time talking about total internal reflection. This happens when a propagating wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. I was excited to talk about this since I am reading many papers on fiber optics and have been considering this as a topic for my project.

During class today Dr. Noé also showed us a demonstration where we viewed a broken clear plastic plate under polarized light. We were able to see how the color pattern of the light transmitted through the plate changed as a result of stress. Since this is a topic that I am not too familiar with I decided to research it more in depth:

Photoelacticity is an experimental method to determine the stress distribution in material. I learned that light moves through transparent materials in the form of waves. The frequency of the waveform varies with the type of light, and these waves vibrate out at a perpendicular angle from the direction of the light beam. When light passes through a polarizing lens, all components of the light wave are blocked except for the components of the light wave in the plane of vibration allowed to pass by the polarizing filter. When polarized light passes through a stressed material, the light separates into two wave fronts traveling at different velocities, each oriented parallel to a direction of principal stress in the material, but perpendicular to each other. For plastics the index value varies as a function of the stress applied, thus Brewsters Law comes into place, which is:

where:

Birefringence results when the stressed material, in our case the clear plastic plate, has two different indices of refraction. From the above equation we can solve for birefringence by determining Δn. By knowing Δn, and the materials thickness t, one can then solve for the retardation, δ.

Which would then allow one to solve for the stress:

where:

February 19, 2015

Today we learned about how we can find a project on our own. Dr. Noé told us to look at previous projects on the LTC website as well as the American Journal of Physics. He asked us again to talk about topics that interested us. Jasmine mentioned that she had previously visited a Science museum in Boston and was wondering about a colored shadows demonstration that she had seen. Having no previous knowledge about this topic myself, I was interested in learning more. Jasmine explained how different colored shadows were formed on a wall by aiming different colored bulbs (red, green, and blue) at a white screen and putting an object in front of it. All together the three colors would form white, but as one of them was blocked, different colored shadows appeared on the white screen. I found this to be very interesting. However, for our project, we need to find something that can be represented by a mathematical model that would fit data measurements. This project was a little too subjective because since everyone sees colors differently, it would be difficult to measure any objective data.

During this meeting I also asked Dr. Noé about fiber optics, a topic that has interested me since high school. He showed me a fiber optics tube and I looked through it and saw how the light was able to bend. A fiber optics cable is made up of many (thousands) of thin glass or plastic strands, known as the optical fibers. This reminded me of a toy every one of my physics classes had, the fiber optics visual stimulator (shown in the photo). During class we would turn it on and even bend the plastic strands and watch how the light still traveled through it.

Figure 2: Fiber Optics Physics Toy

Following this topic Dr. Noe talked more about simple experiments, such as adding corn syrup to water and shining light through it. He explained how the index of refraction changed as the depth changed. All of these conversations will hopefully help me have a topic to research by the next few classes.

February 12, 2015

Today was my first official day at the Laser Teaching Center. Previously, Dr. Noé discussed the process of finding a topic and creating a project, so in preparation I researched a couple of topics that had interested me when I took physics in high school, including fiber optics and lasers. However, I have not had much experience with optics in the past, so I was interested in hearing about the experiments that previous students had completed. Dr. Noé explained a range of projects from measuring the reflective properties of snow to creating a thin soap film on a surface and exploring the optic characteristics of that.

Dr. Noé then asked us what topic we were interested in learning more about and I asked him about lasers. He showed us a demonstration with a laser that shined from across the room. He then asked us questions about how the laser would look if it were brought closer to where we saw the light vs. how it would look if it were farther away. Rachel and I agreed that the laser appeared clearer if it were closer, so then Dr. Noé asked why this was true. I replied that this is because the beam of light gets larger with distance; I remember learning in physics class that with more distance, the same photons need to be distributed over a larger area, thus light density decreases and the beam gets dimmer. Dr. Noé also asked how big would a laser has to be if we wanted it to point it on the moon and reflect back. Rachel and I decided that it would have to be a bigger laser than the one shown in the demonstration but we do not know the exact size. Dr. Noé explained that people do reflect lasers off the moon by using mirrors that Apollo astronauts left on the moon. He asked how one would figure out how long it took for the light to travel there and back. This question involved using estimation and exponents, topics that we had always used in math class, but were not putting them to the test to solve this problem. Working together we estimated the distance to the moon to be about 380,000 km, which would be 380,000,000 m (or as Dr. Noé put it the distance a car would be able to travel before it broke down). Then we knew we had to divide this value by the speed that it takes light to travel, as well as multiplying it by two, since the light was reaching the moon, as well as traveling back. We were able to find the following:

2(380,000,000)/2.99 * 10^8) =2.54 secondss

Seeing how just by thinking about a topic could lead to us solving a mathematical problem and finding such a value was very interesting. I am excited to further discuss applications of ideas in our next meeting.

Figure 1: Apollo 14 mirrors left on the moon by astronauts

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