Research Journal

September 3, 2009

It's the start of Fall 2009 already! I can't believe I have been in Stony Brook for a year. Freshman year flew by quite fast. Summer was mostly relaxing for me as I went back home to India after a year. Sadly I had no activities related to physics or even for the matter science in general. I did try to finish my webreport by accessing SSH client from India but surprisingly I wasn't able to connect. SSH client declared me as an outside entity and wouldn't allow me to log into my profile. Towards the end of the summer however, I took a 2 week internship at an engineering company and learned the basics of computer networking. I am excited to get back to work at the Laser Lab finish my web report and conclude my project properly.

May 11, 2009

After staying in Dr. Noe's lab till 12:00 a.m. some nights I am delighted to inform everyone that I am finally done with the URECA program. It was very exciting to be surrounded by so many enthusiastic scientists and professors. I successfully explain my project to many visitors. Moreover, my WISE 187 presentation went very well. Most of my classmates thoroughly understood my research. Now begins the long drawn process of the online report which I should have up soon.

Monday, April 20 2009

I proceeded to the blue laser today as I am done with the red wavelength for both the plates. The set up for the experiment was identical to the red laser except for the Ne laser being replaced by the Ar laser. My readings weren't quite as accurate as for the Ne laser as the Ar laser was slightly unstable however, for the most part the readings did coincided with the theory.

Friday, April 17 2009

Dr. Noe was away today for a conference at RIT, Shannon and I were told to go to the lab and continue with our experiments. I spent an extra day last week as well, to discuss my progress with Dr. Noe. So far I have conducted an experiment to prove Malus's [Result] The result was astonishingly accurate and the theory curve matched the experimental data points almost perfectly. I was delighted to find only two or three points of deviations. I carried on from there by conducting an experiment using the two spectrum plates. The setup consists of the HeNe laser, then the spectrum plates followed by the analyzer and photodetector. The linear polarizer side of the spectrum plates was facing the laser and the retarder side faced the analyzer/photodetector. Moreover, I oriented the HeNe laser such that the analyzer dial was set to 0 degrees and the photodetector read the maximum intensity for that angle. I also found that if I oriented the spectrum plate horizontally the intensity of light passing was less that if the plate was oriented vertically. Hence for the experiment I set the orientation of the plates to be vertical. I proceeded to increment the analyzer angle by 5 degrees and recorded the intensity of the laser light. Lastly, I repeated the same experiment for the second plate.

Monday, March 20 2009

As I had missed class on Friday, we spent the entire class period writing my abstract for URECA. It is finally finished and I plan on returning to the lab on Wednesday to record a few new measurements and accelerate my progress in the project.

Monday, March 23 2009

Dr. Noe and I made a bit of progress with further measurements on the relation between the intensity and angle of the unknown polarizer with respect to the axis of the laser. I finished taking measurements of the last two unknown polarizers. The next step is to further analyze the relationship between the retarder in these plates and wavelength.

Friday, March 20 2009

I am happy to announce that I have finally started learning about the Jones Matrix. The Jones Matrix is an efficient way to represent polarizers using matrices. It provides an effective method for us to work through the mathematical aspect of polarized light. I am slowly beginning to grasp the concept and since I am taking a linear algebra course this semester, I find it easier to understand the transformations and equations.

Monday, March 16 2009

When Shannon and I entered the laser lab, we were surprised to find Dr. Noe speaking to someone we didn't recognize. He was a graduate student assigned to teach the next batch of WSE 187. Shannon and I spent a few minutes describing our projects and suggested a few ideas in what the next group might be interested in learning about. After he left, Dr. Noe and I finally began our first experiment which concerned measuring the intensity of the red laser light passing through both sides of the circular polarizer. At this point, the only task to complete is to plot the theoretical values against the observed data points.

Friday, March 13 2009

I ran to the projector once the clock hit 12:50. I was so eager to play with my polarizers. Dr. Noe explained thoroughly how circular polarizers work and I finally feel that I am able to grasp the concept of circularly polarized light. We further discovered that most probably both the unknown polarizers were circular polarizers. I also learnt a lot about half wave plate and quarter wave plate retarders. Circular polarizers consist of a linear polarizer and a retarder generally a quarter wave plate. It is necessary for circular polarizers that the retarder is placed in front of unpolarized light first. The fascinating fact that Dr. Noe told me was that if circularly polarized light is passed through a circular polarizer. It comes out of the quarter wave plate as linearly polarized light thus when it passes through the linear polarizer you either get absence of a color or the color. All in all, it was a highly productive day.

Monday, March 9 2009

After overcoming one week of sore throat and coughing, I was glad to be back at the Laser Lab. I had missed the exciting colors of the polarizers. I was very thrilled to open up the package that had been shipped a few days ago which contained the unknown polarizer Dr. Noe had ordered for me. Dr. Noe and I discovered that there were two of them in there. We started off by experimenting with linear polarizers and putting them on top of each other. However, end of class came too soon and we had to leave our experiments in the middle. I can't wait until next Friday to play with them more and explore into depth what they are.

Friday, 27 Februrary 2009

We had quite a fun day at the lab today. For the first time, we had visitors. A few of Shannon's and my friends from our physics class came over to say hi to the little pig. Shannon and I got carried away and showed them all the neat toys like the mini bank etc. They stayed for almost the entire class period. We also viewed the effect of a circular polarizer. Dr. Noe explained in depth how circularly and elliptically polarized light is formed. Once Shannon left he also discussed with me a few possible experiments to perform using the sugar syrup and polarized light. Though it was not a highly productive day it was very entertaining.

Monday, 23 February 2009

Unlike the last few class periods, this time we spend the entire time deriving young's double slit experiment formula. It was fascinating to learn that even though we started by representing waves in terms of imaginary numbers, the expression for the intensity of the wave pattern was a real entity. I further discovered that after working with all the complicated jumble of e, iota and trigonometric functions , as expected the intensity could be expressed in terms of cos^2(theta).

Friday, 20 February 2009

Today's class was rather fascinating as there were a lot of demonstrations. Dr Noe and I also discussed my future project ideas and I was enthralled by all experiments he did. I think I am interested in doing a project in the field of polarized light as it is the fundamental concept behind LCD [Liquid Crystal Display] screens. As discussed earlier, electromagnetic waves consist of electric and magnetic field vectors. For polarization the electric field vector is considered while the magnetic field vector is disregarded. Dr. Noe discussed mainly linear polarizer which converts un-polarized light into a beam of single polarization state. The simplest polarizer consists of polymer chains oriented in a particular direction so as to resemble a wire-grid. The electric field component perpendicular to the orientation of the molecule chain is able to travel through the grid. On the other hand, the electric field component parallel to the 'wires' is absorbed. The transmitted wave has an electric field in the direction perpendicular to the wires, and is thus linearly polarized. [Image]

I observed linearly polarized light using a polarized light detector. I was awestruck to see how different materials such as plastic spoons appeared different colors in different parts. This is observed in any object that has been subjected to stress. Dr. Noe moved on to show us the diffraction pattern of a laser beam and we derived the Young's formula. The most exciting piece of information he shared with us today, was the proof of 'the most beautiful equation in math' { e^(i*pi) +1 = 0}, which incorporates the 5 most basic concepts in math.

Monday, 16 February 2009

In today's class we picked up from where we had left off from last lecture. In the last lab session we had gone outside and formed the image of the sun using three different lenses; 1.25, 1.5 and 2 Dioptres. By measuring the height and the distance of the image at which it was in sharp focus, we had noted that for most of the lenses the dioptre value is equal to the reciprocal of focal length measured in meters. As we know that the angular size of the Sun is 1/100 radians, today Dr. Noe had us calculate the distance at which a 5 inch tall light source would have to be placed in order for it subtend the same angular size as the sun. We calculated that to be 500 inches. Thus, Dr. Noe placed an incoherent light source at a distance of 500 inches. We used the 1.25 and 2 Dipotre lens from last time to form the image of the light source on the back wall. As expected we found the focal length to be the reciprocal of the dipotre value. Moreover, using the moon stick we discovered that the angular size of the light source was equal to the angular size of the Sun. We also found that the angular size of Alpha Centauri, the brightest start in the southern constellation, is 0.5 * 10^-7.The most astonishing discovery was that for an object one meter tall, it would have to be placed 20,000 km away from a point in order for its angular size to be equal to the angular size subtended by Alpha Centauri.

Friday, 13 February 2009

Today was a very productive lab session. Dr. Noe started the class with a lecture on optics. We talked a lot about the nature of light and light rays, including reflection, refraction, diffraction and interference. Light is an electromagnetic wave; electric field and magnetic field along with being perpendicular to each other, are also perpendicular to the direction of propagation, hence light is a transverse wave as well. We also discussed Fermat's Principle, which states that light will take the quickest path possible to reach its final destination. Furthermore, we learned about two laws: law of reflection and Snell's law. The law of reflection states that the angle of incidence and the angle reflection are equal when light strikes a reflecting surface, and Snell's law states the behavior of light rays as it travels from one medium to another. We briefly discussed Huygen's principle and its role in diffraction and interference. The principle states that each point on a wave front generates new wavelets and when you connect the wavelets tangentially you form a secondary wave front.

Most importantly, Dr. Noe explained the concept of angular size. For example, the angular size of the moon is about 0.6 degrees; it is [simply] the diameter of the moon divided by the distance of the moon from the earth. The idea of angular size comes from the fact that for a very small angle the sin [sine] of that angle is approximately equal to the angle, this can be proved using infinite series.

Lastly at the end of class we went outside and observed shadows. An important question arose as to why the shadow is sharper when the object is closer to the wall, on the other hand the shadow is blurry when the object moves away from the wall. Upon researching, I have hypothesized as to why we observe this phenomenon. Due to the large size and distance of the sun from the earth, the angular size of the sun is very small and we can consider the sun as a number of point sources. Due to the multiple light sources there are multiple shadows. Since these points are in different directions with respect to the object, when the hand is closer to the wall the relative angular separation between the shadows is less hence a sharper image is formed. On the other hand when the distance between the hand and wall is greater, the difference between angular separation is greater thus, the shadow is blurry. [revise per discussion today]

Monday, 9 February 2009

Dr. Noe started today's lab session with a lecture on html coding and showed us how to handle browsers and html text files; only later did we find out that we were to 'burn' paper outside. As everyone might have experienced in middle school, you were handed a magnifiying glass and were told to try and burn a piece notebook paper using the mundane object. As a child, I was astounded as to how to go about the task but I soon learned that the magnifying power of the small lens was quite extraordinary. It was unexpected that for our lab session today Shannon and I were to revisit our old school days and burn the black piece of paper given to us and observe as to what will happen. Although, I already knew how the lens magnifies the sun's rays at a single focal point I soon observed other phenomena. It was exhilarating to find that if one looked near the burning spot, you could view the sun's rays in the smoke emitted from the spot. Shannon also discovered that behind our black paper a circular rainbow formed on the ground replacing the shadow of the hole. I thoroughly enjoyed playing with the magnifying lens as I attempted to burn my name on the piece of paper.

Himadri Kakran
February 2009
Laser Teaching Center