## My Journal

July 1, 2003

Dr. Noé showed us something cool on the second day of the program, since we didn't know what to do. First, he showed us the structure of a "pinhole camera," a simple camera that uses a tiny pinhole to focus instead of a double convex lens. The advantage of a pinhole camera is that there is no limiting distance between the pinhole and the object. However, there is a limiting size of the pinhole. If the pinhole is too small, the diffraction pattern will ruin the picture's quality. If it's too big, you don't necessarily get an image, at least not something that are clearly recognized as images. (Wow!) Actually, the pinhole camera has a very important role in determining the size and the shape of celestial objects, although we don't use it as often. We went outside that day, set out our pinhole camera, and collected some data. (It was nice out! We also played with polarizers.)

July 2, 2003

I TRIED to learn about Nonlinear Optics. It finally turned out that I need a lot more knowledge of optics to handle this area. So, I tried to understand how lasers work. (What a jump.) Two very important parts that make lasers function are "Stimulated Emission" and "Population Inversion." (Cool stuff.) Also, for the first time, I heard about the "metastable levels" within the atoms. In ruby lasers, electrons are pumped from the ground states to the levels with higher energy, and therefore create the population inversion. The electrons will spontaneously fall to the metastable level and stay there for a certain amount of time, which is the lifetime of the metastable level of atoms. This rapid transition of electrons involves no emission of light; instead, the energy released in the transition is dissipated as heat in the ruby crystal. (O) That's why the energy of light emitted from the lasers is always less than that of the input energy.

July 3, 2003

It seems that everybody here knows what "Doppler Shift" is and it sounds quite important. So I started to learn a little bit about it. Doppler Shift, discovered by a guy named Doppler of course, is a shift in an object's emitted wavelength due to a motion relative to the observation point. It is actually a very common phenomenon. The siren's pitch changes as the vehicle races toward, then away from a person, is one of the observations of the Doppler effect. We can actually determine how quickly an object is moving or determine the rotational speed of the sun by studying its Doppler shift.

July 4, 2003

## OFF

July 7, 2003

Dye laser is a special kind of laser. It's special because the wavelength of the emitted light is tunable, covering a range from 570 to 650 nanometers. The dye used is called Rhodamine 6G, or Rhodamine 159 chloride (C27H29O3N2), which has a very complicated structure formula. In the afternoon, Professor Metcalf gave us a speech on interferometers, on Fabry-Perot specifically.

July 8, 2003

Among all the crystals, most are clear. However, if you look through them, you don't necessarily see AN image of the object at the other end of the crystal. YOU CAN SEE TWO!!! This is called double refraction, or bifringence. If a beam of light, any kind of light, shines through this kind of crystals, for example, calcite, along its optical axial, two beams of light will be observed coming out of the crystal. AND THESE TWO BEAMS OF LIGHT ARE BOTH POLARIZED!!!! THE POLARIZATIONS ARE PERPENDICULAR!!!!! (Isn't that amazing? I got all excited when I was learning about it.) These two beams are called the ordinary ray (o-ray) and the extraordinary ray (e-ray). O-ray travels at a constant speed towards any directions, however, e-ray travels at different speed in different directions. Only when the light shines through the crystal along its optical axial both o-ray and e-ray travel at the same speed. (Wow!) There are lots of fun things you can do with these kinds of cool crystals (Actually, the most commonly seen ice cubes can do the same thing). They also have very important applications in laser industries, such as frequency doubling. Most of these crystals have only one optical axial, however, some special crystals have two. I have never seen any of those before, but I read about that even much cooler things can happen if light is shined at them. I was happy to learn these cool optic stuff.

July 9, 2003

Nowadays, Compact Discs (CD) are very common and useful in both data storage and entertainment. However, not many people know, at least I don't know, about how CDs work. I did a little reading on how CDs work. Normally, a single sided CD can store 74 minutes of music, or more than 780 megabytes(MB) of digital data. In order to understand how CDs work, we need to first understand the structure of the CDs. A single sided CD has four layers, the label, a thin layer of acrylic, which protects the aluminum layer underneath, and a layer of polycarbonate plastic at the bottom. The plastic is impressed with tiny little bumps or pits arranged as a single, continuous, and extremely long(about 3.5 miles, or 5 kilometers) spiral track of data. (Amazing!) For more information on how CD players work, click here

July 10, 2003

I still don't know what my project should be. During the pizza lunch with everybody (We, every one in the Laser Teaching Center, always gather together on Wednesdays, in a room that is so cold that you would sweat outside of it, to talk about everybody's projects and important upcoming events), I told professor Metcalf that I WAS interested in Laser Cooling. "It sounds great! So you can work with James." Well, it sounded great to me at first too. After talking to James about it and reading articles on Laser Cooling and Bose-Einstein Condensates, however, I didn't think that it can be my project, too much for a high school student.

July 11, 2003

In the morning, I wanted to know how tomography works. ('coz it sounds really cool to me.) I found how CAT works at www.howstuffworks.com. (It's a really cool website. Yiyi told me about it. Thank you Yiyi. Yiyi also told me how to link.) On the same website, I found an article on Parkinson disease. To my surprise, an experiment done among thousands of Japanese people showed that people who drink coffee on a regular base are five times less likely to get Parkinson disease than the people who don't, however, according to the article, there is no apparent link between coffee and the causes of the Parkinson disease. (Anyway, i decided to drink more coffee from now on.)

Finally, I got something to do, not my project yet. Dr. Noé showed me something called "diffraction gratings." (Never heard of it before.) Using those gratings, we can determine the wavelength of the incoming light relatively accurately, if correct measurements are done. So, I set everything up, including a HeNe laser, a diffraction grating, and a piece of graph paper. (pretty simple) As the laser was turned on, a beam of red light (632.8nanometers) shined through the grating which was perpendicular to it. On the graph paper at the other end of the grating, more than one red spot was observed. By measuring the distance between the first-order dot and the second-order dot, and the distance between the dots and the grating, I was able to get the spacing of the grating, using the equation, . Then, I could use the same setup, with a different laser with unknown wavelength and do the same calculations, to determine the wavelength of the laser. After two trials, I got the wavelength of the green light out of the laser pointer, 537 nm. The actual wavelength should be 532 nm. E%=1.03%. ("Not too bad." said Dr. Noé.)

Something cooler happened later. While I was playing around with the grating, Patrick the Grasshopper (I don't exactly remember why he was called the grasshopper. It has something to do with the laser pointer tips, according to Sage. Whatever.), intelligently asked: "What if you shine the flash light at the grating?" ("What if" is Pat's "Pet Phrase"-don't know what it means.) We did. Wow! Click here to see what we saw! Also, this was the origin of the idea of the "Rainbow Pig."

July 14, 2003

I continued my work with the diffraction grating. The grating was perpendicular to the laser and the graph paper. My job today is to change the angle of the grating. If the wavelength of the laser light is provided, using a very similar equation, we can calculate the spacing accurately. It's kind of unnecessary since I already knew the spacing through the much simpler experiment I did last Friday. However, I found something interesting. When I turned the grating to the right, the first-order on the left was farther away from the zeroth-order than the first-order on the right. As the grating was turned further, the spot on the right began to move towards the zeroth-order spot, then stopped at a "limit" and started to move to the right again. This way, I obtained the spacing distance between the the grooves, 1338.2364 nm. E%=.37% (I'm happy about that #.)

July 15~July 21, 2003

Recently, I am obsessed with the "Quantum Dots." They are really amazing nanomaterials. Quantum dots are usually made up of thousands of atoms of semiconductors. If light is shined on these man-made tiny particles, quantum dots will emit light. The amazing part is that, quantum dots can emit multiple colors, almost all the colors on the visible part of the spectrum. The light emitted is very sharp and it lasts for much longer time than that of the organic dyes.

PS:July 17 is Yiyi's birthday!!! Happy Birthday, Yiyi!!!

July 22, 2003

Out of boredom, I came up with some fun ideas. I sticked the little pink pig that was in the lab onto one of the flashlights. As the light was turned on, through a double convex lens, the inverse image of the pig was shown on the wall. If a grating is added between the lens and the wall, the white ligth coming out of the flashlight would be diffracted into light with different wavelength that made the white light, similar to the visible spectrum. The pig was then called the "Rainbow Pig." There was a little problem when I was trying to show Dr. Noé my "Rainbow Pig." I couldn't get the pig to focus. Then I found that in order to obtain a sharp image, the distance between the object and the image have to be at least four times of the focal length. I held the light too close to the wall. Also, I found another cool website where you can do experiments on line.

July 23, 2003

ALex Ellis, a genius Simon Fellow who did research on laser modes in Laser Teaching Center last year, visited. That was the plan for the day.

July 24~July 25, 2003

Matrices are frequently used in optics. I decided to give it a try today. I first learned about the ray-transfer matrix, and then many matrices of simple optical components, such as free-space propagation, transmission through a thin lens, etc. Also, I learned about matrices of cascaded optical components and periodic optical systems. They looked easy based on definition. However, it took some work to figure out the solution in practical applications. I was happy about what I've learned today.

PS: July 26 is Oleg's birthday!!! Happy "Birdsday," Oleg!!! Blood forever!!!

July 28, 2003

I excitingly told Allison that tomorrow is my 17 and a half birthday. However, I was wrong. My God, I can't even count dates properly, although I'm not Christian.(?)

July 29, 2003

I learned something about making spectrometer based on the Talbot Effect, a topic Allison has been working on. For more information, try the paper written by Helen Kung.

July 30, 2003

We, most of the Simons kids, visited Brookhaven National Laboratory (BNL). It was very exciting and I think I learned a lot. However, I'm lazy, so for more info, look at Sage's, Yiyi's, and Maanit's journals.

July 31, 2003

REU presentation!! Every one did a great job. Actually, Yiyi and I went in there half way through, and had free lunch with other kids in both REU and the Laser Teaching Center. In the afternoon, I played around with Allison's Talbot setup.

Aug. 1, 2003

I kept playing with the Talbot setup. I added a double convex lens with focal length 300 mm between the fiber and the grating. Using Matrices, I was albe to get the position of the actual light source (for that the lens changed the angular divergence of the light), which was 255.51 mm away from the grating. The original purpose of the lens was to make the light parallel, so that according to the lens equation, the focal length would appear periodically, and the places where images were observed would be seperated by an equal distance. Anyway, the figures I obtained from calculation and from experiment almost tallied with each other. Also, I successfully graphed the data using Microsoft Excel.

Aug. 4, 2003

Today is the actual day that I started to edit my journal, bio and everything on my web page. (It was totally empty before.) Sage, Yiyi, Maanit, and "Prof. Jose" etc. all helped me to make my web page look nice. Thank you all!! I tried my best to write whatever I remembered and whatever that was on my notes. Finally, I said to Yiyi, "Writing journal is really time consuming." However, I felt happy for what I've "accomplished" today. I got a nice web page now! (Yeah!!)

Aug. 5, 2003

Got an email from Karen Kernan, the lady that was in charge of the program. She said we had to hand in our abstracts before next Monday. My God, (again, I'm not Christian and I don't believe in God) I don't even know whatever I have been doing for the past five weeks, at least, not one single theme. It bothered me for a while because I had no clue what to write about. Then Dr. Noé suggested that I could write about multiple things that were related. So, with Dr. Noé's help, I got my abstract done.

Aug. 6~8, 2003

I "robbed," (actually borrowed, but he was not very willing to lend us because of understandable reasons) the Pabry-Perot Interferometer from the "Big Oleg". So I played with it. Also, I needed to use part of James' super setup. Unfortunately, I almost ruined his entire thing. (Shh, don't tell him about it!) I looked at the different modes of laser on the oscilliscope, by shinning laser light through the Fabry-Perot cavity, onto the photodiode behind which was connected to the oscilliacope. If a polarizer was put in front of the short HeNelaser, only one mode can be observed at one time. If the polarizer is rotated, we can see the modes, or frequencies changing on the oscilliscope. We were, luckily, able to get pretty sharp peaks. However, we always got two dots out of the interferometer. What I was supposed to do was to couple the light correctly and therefore I would be able to get only one dot.

Aug. 11~12, 2003

I've been doing stuff related to the Rebry-Perot interferometer. In order to couple it right, I needed to calculate the beam waist and the curvature of both the light wavefront and the two end mirrors (they are actually coated lenses).

Aug. 13, 2003

Evan Marshak, another former Simon's genius, visited.

PS: Today is Doug's 23rd birthday. Happy birthday!!

Aug. 14, 2003

I measured the focal length of one of the lenses. This was difficult since the lens was coated and it allows only 1% of the light to go through. It was almost a reflective mirror. So I first used an already expanded light, made it parallel, then I put a piece of glass between the lens and the parallel light source so that the light would focus onto the mirror. Through fine measurement, I was able to get the focal length of the lens, which was 23.94 mm.

I was planning to get more stuff done, however, at around 4pm, the power was off. Some people thought it was another terrorists attack. It finally turned out to be that a little Integrated Circuit somewhere was broken which caused the "mast darkness." All northeastern states and part of Canada had no electricity at all until the next day.

Aug. 15, 2003

There was supposed to be a Simons presentation during the afternoon. Since there was no power supply, the presentation was cancelled. However, there was electricity in most part of Long Island, so I thought that there should be electricity in the university too. My dad dropped me off at around 9:30 am. I found out that there was still no electricity in the university since they had to store energy, however, after my dad left for work. He had to come back to pick me up again later. Sorry, dad.

Today might be the last day I can ever seeSage and Jose. They are leaving us.(Sad.) I'll miss them.

Aug. 18, 2003

Today i forgot to log off

PS: Today is my mommy's birthday!!! Happy Birthday, mom!!! It's also Pat's "birdsday"!!! Happy birthday, grasshopper!!!

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