April 30, 2015
This morning I called ThorLabs at 1-973-300-3000 to ask about the tail at the end of the spectral lines. Tech support hadn't heard of issues like this, and suggested that it was because of the resolution limit of 0.5nm. In either case, I was given an email to send the files that displayed this problem, along with specifics of the light source recorded.
In addition, I asked how the spectrometer works. Within, there is a grating through which the light is diffracted into components. This comes to a linear ccd array, as opposed to a vertical array. ThorLabs has included a known source and corresponding data which serves as a calibration. I am not familiar with the term "linear ccd array," or how it's different from a vertical, so I will look into that. Perhaps that is where the tail originates, or a malfunction within it.
April 24, 2015
I met with Dr. Noé today to record the spectral analysis of the sodium lamp at different times, so that at the beginning I can capture the spectrum of the neon-argon mixture, then the sodium as it becomes brighter. I captured the spectra using the ThorLabs software and saved the files at different times, including about 30 seconds after first light, 60 seconds after first light, and 5 minutes after first light.
We noticed a strange curve shape at the end of each spectral line, where the intensity shallows off like a "tail" or a "swoop." We recorded the spectrum of a few different lasers, including a red helium-neon, and a green argon at 487.6nm. These also showed a tail, even though the approach to the line's peak is straight. For now, it is unknown why even the most precise, monochromatic lasers display this effect, or, rather, why the spectrometer (either hardware or software) produce this.
Finally, we recorded the sodium lamp through a polarized filter. Overall, there are five files saved for the sodium lamp and three for different lasers. Due to the nature of the software, I cannot have it on my laptop (a MacBook Pro), so I will continue to analyze the data when I have time in the lab to do so.
April 23, 2015
Before class today, I researched the type of lamp we are using. It is GE NA-1 Sodium Vapor Spectral Lamp, G5CL. This is listedas a low pressure sodium (LPS) lamp, and contains trace amounts of argon and neon in what is known as a Penning mixture. This type of mixture is made of an "inert" gas and a "quench" gas, which has a lower ionization energy level than the inert gas. By having a very small fraction of the quench gas and the vast majority as the inert gas, the gas mixture is easier to ionize than either gas alone. Neon and argon mixture is commonly found in neon lamps, and is used in the LPS lamp to warm and vaporize the sodium metal within.
Furthermore, neon has a strong spectral line at 588.2nm, which is very close to the 589.0-589.6nm produced by the sodium. The two peaks I saw the first time I used the spectrometer may have shown the neon line and a sodium line instead of the two d-lines from sodium alone. Argon has spectral lines in the red, green, and blue parts of the spectrum, which we see as kind of purple-y when the lamp is first heating up.
During our meeting, Dr. Noé brought up the fact that when the lamp is warmed up and primarily yellow from the sodium, it seems opaque. This may be because the photons are constantly reabsorbed and re-emitted by the sodium within the lamp, which makes sense for the properties of a vapor.
April 16, 2015
I missed last Thursday's meeting due to a medical emergency, and was unable to work on my project in the lab with Dr. Noé.
Today, Zheni presented her project's progress, which involves the physics behind the retroreflector on the moon and how it affects the lasers that travel there. She has been using the model retroreflector in the lab with the heavy duty helium-neon laser, although she's having trouble resolving the returning light. Jasmine talked about her project with polarization. She taped together triangles of a polarized transparency film, held it over a light source, and demonstrated the Maltese cross. This cross shows a black "X" where the polarization of the material determines whether or not light travels through it.
This was the second time I presented to my peers, and was able to talk about the specifics of the physics behind the research, including important figures I didn't have before. Dr. Noé, though, directed the conversation towards what I had actually done with the experiment portion, which hasn't progressed much since he first time Dr. Noé and I looked at the lamp and spectrometer. So for the next week, I will look up the type of lamp we are using (low pressure versus high pressure) and its properties.
April 8, 2015
Today I visited Dr. Noé to discuss two topics: how the spectrometer works, and how to write an abstract. The abstract was due today, but according to Dr. Noé, it needs to be heavily revised. I'm rather conflicted about how this project is developing. I was first interested in it because of the sodium D-Lines, but the first run through of the ThorLabs system showed two distinct lines at about the wavelength range we were aiming for. In short, a project solely based on the d-lines is too easy and shallow. Now I am looking into the composition of the other gases within the lamp, what kind of lamp it is (low-pressure versus high-pressure), and how the spectrometer works. I don't like how the research is moving away from solely sodium, but, then again, I'm not working with solely sodium. I guess that's how research works: It expands upon different aspects as it develops.
The spectrometer takes light in through a fiber-optic cable and focuses it using a lens onto a detector, which then converts the light information into information for the computer. Unforunately, we cannot open our spectrometer to look inside, yet generally this is how small spectrometers work. I will look further into this, although the website for our ThorLabs spectrometer includes the specifications for the instrument, and not the inner workings.
I will work on revising my abstract, which will have a bit of "wiggle room" with the deadline. Some corrections Dr. Noé suggested include changing "split" to "resolve," "would like to investigate" instead of "expect," and watching the tense. I should focus on more than just the d-lines, since that is how the project is changing, and keep in mind the audience.
April 3, 2015
Today I spent an hour with Dr. Noé looking at the sodium lamp and spectrometer. There is an old computer with the software already installed, but it also has some issues with other programs on the computer that severely limits my use of the spectrometer program. For instance, a window pops up right over the right half of the x-axis (which indicates the wavelength of the light), and refuses to close. It's very frustrating, and I hope to find another computer to use for the actual experiment. The software only works with Windows Vista and Windows 7. I have a MacBook and an Asus tablet which runs Andriod, and neither can run the program. Thinking, back, I could have asked Dr. Noé if we could install the software onto the computer in his office.
Right now I need a computer with Windows that can take in the software. Dr. Noé gave me a little green LED keychain to test out the software should I get it running elsewhere. I'll need to have the program in the LTC, since that's where the sodium lamp is, so the computer can either be a laptop or Dr. Noé's computer. I will try and test some of the analysis and math functions the program offers this weekend and week, specifically getting numerical values for the multiple data points the spectrometer collects. Fitting a curve to a very narrow peak in the spectrum, like that form the LED, will help me understand how the program finds the max vlaue, even if the value isn't directly taken. Then, Dr. Noé explains, I can take this curve and fit it underneath a broader curve, such as the few we'll get from the sodium lamp, in order to find how far off the program's interpretation of the maximum value is from the actual max. I'm still a bit uncertain as to the math behind these calculations; nevertheless, I will try and find an appropriate computer for the software, take readings from the LED, and fiddle around with the functions.
The abstract is due this Wednesday, so I will also be focused on that. I'll look at example abstracts and fit my own to the style and formatting I find. I hope to be ready to take measurements fromt the sodium lamp in two Thursdays, which gives me a little less than two weeks to fully understand the software.
April 2, 2015
Today we presented the basis of our projects to the rest of the group. Jasmine plans to work with polarized light and explained to us how light can be filtered using a crossing pattern of different indexes of refraction. It seems pretty complicated, and I don't understand the scientific reasoning behind all of the results she plans to get, but the overall concept seems very interesting.
Zheni has been interested in lasers and the retroreflector Dr. Noé has, and will do a project based on the idea of light being reflected from two mirrors which meet at a right angle. She may test the reflective properties of non-flat mirrors and use lenses in front of curved mirrors to redirect the light going in and coming out. I find it fascinating that an everyday object like a mirror still undergoes experiments based on teh properties of reflection and reflective angles.
I was not very prepared for today's meeting, and struggled to explain the details of the underlying physics and chemistry of excited sodium. I was given the spectrometer to examine and play with. I will meet with Dr. Noé tomorrow to actually see the sodium lamp and find out how to operate the spectrometer and its software.
March 26, 2015
After much discussion with Dr. Noé, it seems that my eye color project won't cut it for the kind of research we're looking for. i didn't want to lose hope in it quickly, so I asked about other potential projects that could replace it, specifically dealing with spectroscopy. Dr. Noé told us about the spectrometer he has but never played with, and that it could take measurements of a sodium lamp he also has. He described a project that could use the spectrometer to separate two spectral lines of sodium, known as d-lines, which are extremely close to each other: Their energy difference comes from the different spin of the valence electron, where one direction requires slightly more energy than the other. This topic easily related back to astronomy, where astronomers have to take very careful spectrographs of distant stars and planets to know their compositions.
In addition to this project, we discussed URECA due dates: The abstract is due April 8th and the event is April 29th. Over the week, we should look at previous projects and work with the Linux system to maintain our web pages. Overall, I left today's meeting feeling more optimistic about this new sodium-spectroscopy project as a good replacement for the eye color project. I'll so some more research on teh chemistry and quantum physics behind it.
March 12, 2015
Yesterday I was talking with a friend who commented on the color of my eyes. He said they're very green-hazel, although I've grown up calling them blue. I hear this a lot - even my optometrist insists they're too hazel to be considered blue. They do look blue on occasion: it's nothing like "the dress." They can be blue. Later that day I Googled "eye color" and read parts of the Wikipedia article. Apparently, the pigment, known as melanin, in the iris is a varying mixture of yellow and brown located at the back of the iris (iris pigment epithelium) and the middle portion (stroma). This along with the cellular density of the stroma makes up the majority of the eyes color. The article continues to say that "the appearance of blue and green, as well as hazel eyes, results from the Rayleigh scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky... Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes" (Wikipedia).
Three things caught my attention: Rayleigh scattering, structural color, and the "light conditions" necessary for eye color. The first two were linked to more Wikipedia articles which describe the phenomena, and I will read them more in depth at a later point. But the third cause, the "light conditions," is not explained further.
This is where I think I can fit a project.
I proposed the topic to Dr. Noé today, who seemed a bit hesitant and uncertain as to whether there is enough physics in it. If anything, my research will prove if there is any physics to it at all. Here's one way I would conduct the research:
I would find 1) a very "pure" white light with a high and equal intensity of red, green, and blue, 2) a number of filters that adjust the intensity of red, green, and blue light that passes through (though the light would appear mostly white), and 3) a high quality camera. I would take a picture of my eye exposed to the pure light, followed by the light through filters. The light would be coming head on, and Ill be wearing black clothing with black surroundings. I could easily change the manipulated variables to include different colored shirts and surroundings, or different angles the light comes in. If I could not find filters, I would use different light sources including sunlight, fluorescent and incandescent lighting, and others, all with a known color spectrum intensity. After all this, I would compare the color at different regions (inner, middle, and outer) of my iris since it appears that the melanin distribution changes as it goes radially outwards.
Fortunately, the project itself shouldn't take too long. It's only a handful of photos, which can be compared digitally. There is a possibility, however, that eye color changes during "puberty, early childhood, pregnancy, and sometimes after serious trauma... based on chemical reactions and hormonal changes within the body" (Wikipedia). This has not been proven and does not necessarily negate the previous assertion of specific "light conditions." If it turns out that the color intensity in light, angle it approaches the eye, surroundings, or other physics related variables have no effect, I could scrap the project and work with the somewhat untouched spectrometer.
The first thing I would do with the spectrometer is find out how it works. It would be nice if that could be my presentation. I think I could make a poster board about it, with its internal functions and features. Perhaps it can even help with the color intensity of light sources for the eye color project. I don't know a lot about spectrometers, so I'll look into the topic more deeply over spring break.
The best thing I can do over spring break is run a mini-experiment for eye color. I don't know if I have a good enough camera, but I can try and see if lighting or surrounding colors or clothing changes the color of my eyes noticeably enough.
In addition, we discussed Snell's law further today during our meeting, including the concept behind the sinusoidal relation between n1/n2 and the critical angle of total internal reflection. It was really fun to have some "Aha!" moments as steps towards a total understanding. I'll be sure to write this, along with my findings on irises and spectrometers, in my brown notebook.
February 26, 2015
Today we focused on the closely related phenomena of refraction and total internal reflection . I had learned about this last year in AP Physics B, and today was a good review. I remembered the equation which describes refraction of light from one medium to another, but forgot some of the crucial concepts behind total internal reflection, specifically which way the light path changes (towards or away from the normal) to approach total internal reflection.
Unfortunately, nothing special or intriguing pops out to me about refraction. It seems to be well covered and explored, so it would be difficult to find anything new to study. This is how I feel about a number of other common topics in optics and waves. The best thing for me to do is study the subject further, becoming familiar with the basics and following obscure sub-topics that interest me.
February 19, 2015
Today we started to think about possible project topics to focus on for this semester. Right now I'm slightly interested in polarization, mostly because I don't understand it entirely. Interferometry and spectrometry were briefly mentioned last week, and I had heard a bit about them in my astronomy class. I want to try and find a topic that relates to astronomy so that I can look back on it a few years from now and possibly expand upon it. If ideas are difficult to find on my own, were told we can look in the American Journal of Physics or other research journals for inspiration.
I would say the biggest issue for coming up with an idea is not having enough understanding of the equipment the LTC offers. There are a lot of routes to follow in optics and waves, and I only know a few.
February 12, 2015
Dr. Noé , Zheni, and I talked about a variety of topics, from laser beams traveling to the moon and back to the use of the LTC website. On the former, I learned about a special kind of mirror apparatus which reflects incoming light straight back, no matter the angle. This means an observer can only see his/her own eye no matter how the mirror is held. Dr. Noé showed us a small replica, and it was quite startling to move it without having the image move as well. We discussed how far away the moon is and how long it would take the laser to travel there and back, and whether or not a laser beam spreads out as it travels. We tested this in the lab, and found it to spread slightly. Despite my intuition, a bigger laser is needed to reduce spreading of the beam.
We then talked about the LTC website and how to submit journal entries and the like. Dr. Noé explained that the system involves Linux and HTML. Jasmine, who couldn't make it today, and I are taking a Computational Science and Engineering sub-course in WSE 187, where we are introduced to Linux. We'll be able to work with the website in no time.
February 5, 2015
Today was my first day in PHY287 and first time in the Laser Teaching Center. To introduce the fun, exploratory side of the lab and of optics, Dr. Noé showed Zheni and me a few neat tricks around the lab. First we saw the mirage device, where two toy pigs are placed within the bottom lid, and a hole in the top lid shows a 3D image of the pigs as if they were floating above the hole. After some thought, I realized the lids were equal parabolic mirrors. Light hitting the pigs reflects off at an angle towards the top mirror, then reflects straight down to the bottom, then at the same angle reflects out of the hole on the top. We shined a laser on to the fake pig and it showed up on the real one within the lids.
Next, Dr. Noé brought out a candle in a square bottom case. He placed a rectangular lid over it, and suddenly a dozen or so candles appeared in a row along one side of the lid with a row on each of the four sides we could see. This is because the sides are two-way mirrors. In essence, we can see what it looks like to put two mirrors facing each other The long line of candles is the image of the candle on the far mirror, reflected between the mirrors over and over again, growing a little fainter each time.
Finally, we saw polarized light through a beaker of special sugar-water solution. It started off red, and as the polaroid plate turned, the color changed, cycling through the rainbow. It was incredibly beautiful, although I don't understand the science behind it very well. It was mostly the chemistry aspect that stumped me, but I could learn more about polarization.