Journal



April 27, 2007 (aka my birthday!):

Today we gave our presentations for WSE 187. I believe that it went really well, and I feel that the audience really enjoyed our presentations.

April 25, 2007:

Today was URECA! Sadly, I was only able to stay there for two hours because I have a lot of classes on Wednesdays, but it was really incredible there. There were so many interesting projects there, and I was able to explain my project to a couple of people. All of our abstracts were even printed in a book!

April 23-24, 2007:

Over these days, we worked like crazy on perfecting our posters for URECA. Finally, at 10 pm on the 24th, I finished my poster. It's perfect!

April 21-22, 2007:

This weekend, I worked on preparing papers for my poster and writing my web report. I also wrote up a speech aout my project that I will use at URECA.

April 20, 2007:

Today, I worked on planning out my poster and making diagrams on linux of my set ups. I was in the LTC for eight hours! I got a lot of work done, and I learned how to use Latex, a program used to make math textbooks.

April 19, 2007:

Dr. Noe had taken some data for the laser's intensity when the prism was angled at 45 degrees, so today I graphed his data on a polar plot. I found that it had a phase shift of 40 degrees. To test the accuracy of these results, I used the formula phase shift = 2arctan(sqrt(I1/I2)). First I place the polarizer right in front of the prism to see when the light would disappear. Then I kept the polarizer set at this angle and set it up with the prism at 45 degrees like usual. I took an intensity reading at this value, and then turned the polarizer 90 degrees and took another reading. These values are used as I1 and I2 respectively. When plugged into the equation, the calculated phase shift was 40.52 degrees, which matches our results very closely.

April 17, 2007:

Today we used a new prism and tried to find its index of refraction. I set up the laser to be at its critical angle, and then used triangle geometry to find the angle that the laser was hitting the prism. With this data, I used a guess and check method with Snell's Law to find its index of refraction. After a few tries, I found its index of refraction to be 1.515. This is the index of refraction that a common glass used for optics, BK7, has for red light, so it's pretty safe to state that this prism is probably made of BK7.

April 13, 2007:

Today, we worked on trying to figure out why the data that I have collected is slightly different that we expected. We thought that maybe this difference is due to a different index of refraction in the glass than we expected. Most glass has an index of refraction of 1.5, so in all of my previous calculations I had used 1.5 as the index. To test this idea, I measured the intensity of light hitting a prism at exactly 45 degrees. I plotted that data and got it to fit on a polar graph with a 47 degrees phase shift. This kind of phase shift should correspond with a higher index of refraction in the glass. But when I tried to make a triangle diagram of what is happening in the prism, a higher index will not work out within the prism. Thereby, we ruled out a different index of refraction. Our next idea is that maybe there is a thin film on the surface of the prism.

April 10, 2007:

Today we worked on planning our posters and trying to figure out what to do next with our projects.

March 29, 2007:

Again, I tried to make perfectly elliptically polarized light. I was closer today and was able to get 49 degree elliptically polarized light. This time I had taken refraction into account.

March 27, 2007:

Today I worked on making elliptically polarized light. I set up the laser and took data, and when it was plotted in a polar plot, it followed the formula that we had derived fairly well. Still, in the end I found that I had made 53 degrees polarized light when I was aiming to make 45 degrees polarized light.[It turns out that we should not have been trying to use 54 degrees to get a 45 degree phase shift as we had originally thought. After we figured out what the graph of phase shift versus critical angle for different indices of refraction, we realized that we should have used a smaller angle to achieve a this.] The error is most likely due to refraction, which I had not taken into account. Later, I also realized that I had mismeasured the length of the wall when calculating the angle to set the prisms at.

March 23, 2007:

Today Dr. Noe helped me figure out the equation for the intensity of elliptically polarized light. After using the Jones Matrix and some trig functions, I was able to get a beautiful graph of what my experimental results should be. If the electric field vectors in the x and y direction are the same, and phi = 0, the Intensity = 1 + 2cos(theta)sin(theta). It was really amazing to see long lines of difficult mathematical calculations turn into a fairly straightforward formula.

March 22, 2007:

Today I worked on recreating circularly polarized light. It was very hard to get the prisms to be at exactly 54 degrees, and we ended up trying to measure the angles of the light to get my set up to be accurate.

March 20, 2007:

Today I worked on making circularly polarized light. Dr. Noe had set up two prisms each at a 54 degrees angle in such a way that when linearly polarizer light was shined through them and a polarizer, the intensity of the light was the same at every angle. Then, if we were to take away one of the prisms and measure the polarized light, it would be elliptical. I worked today on making the circularly polarized lgiht as perfect as possible.

March 16, 2007:

Today, Marissa and I joined Christina and Eva in the LTC, and we stayed late working on our projects. WE found out that the irregularity in my intensity results was not due to a smudge; the laser that I was using was not level, so the laser was shining through the polarizer at an angle. We leveled the laser, and then redid the experiment. The results that we got this time were much more accurate and made an even better cosine squared curve.

Next, I took a piece of transparent plastic wrapping and fitted it to a lens holder. I placed it in front of the polarizer, and next time, I plan on taking intensity readings through a plastic and polarizer.

March 15, 2007:

Today we finished collecting our data and graphed the points that we had found. Sure enough, our points looked very similar to a cosine squared graph, but in the middle range of our graph (about 130-270 degrees) was not fitting perfectly. Our maximun at 195 degrees did not reach the same intensity as our maximum at 15 degrees, even though the intensities should be identical. Later, when we removed the polarizer, we saw that there was a miniscule smudge on the polarizer right around where our data was off target. We hypothesized that the smudge absorbed some of the laser's intensity, making those data points lower than they should have been. It is definitely important to not touch the lenses in the lab!

March 13, 2007:

Today we began to take more precise data. We measured the intensity of a polarized laser through a polarizer at two degree intervals. While doing this, we noticed that the reading that were recorded at its maximum intensity kept increasing as time went by. It took about twenty to thirty minutes for the laser to warm up and for the reading to remain constant. From now on, we are going to have the laser warm up before we arrive to work with it.

We found out that the laser that we are using is currently oriented with maximun light intensities at 15 and 195 degrees and minimuns at 105 and 285 degrees. We ran out of time before we finished recording the data but plan to continue with the data collection during the next class.

March 8, 2007:

Today we got to begin taking measurements. We measured the intensity of a polarized laser through a polarizer at twenty degree intervals. When I graphed the data, I was able to see that indeed the intesity reached a maximum at 0, 180, and 360 degrees and a minimum at 90 and 270 degrees. This proves that if you turn a polarizer with minimum light passing through ninety degrees, you will reach an intensity maximum. Also, the graph of this data was a graph of cosine squared. One strange thing that I noticed while taking data was that at the light's intensity maximum points, the intensities recorded fluctuated a lot, whereas lower intensities were nearly constant.

In addition, we used the polarized laser to view an airy disk. We shined the laser through a small hole and the airy disk appeared. Then we placed a lens in front of the small hole, and were able to see that the lens made the image stronger.

March 6, 2007:

Today we discussed polar coordinates and graphed them. Also, I got to try shining a polarized light laser through a polarizer. I made the light almost enitirely disappear, and then turned the polarizer ninety degrees to see the light at its brightest.

Also, I wrote up a basic summary of polarization using Giancoli 6th Edition Physics and wikipedia:

Polarization is a characteristic of electromagnetic waves like light that show the direction of their transverse electric field. This property only exists for transverse waves (not longitudinal sound waves since they oscillate in the direction of the wave). A wave is linearly polarized.

Maxwell theorized that light was an electromagnetic (EM) wave. It predicted that light can be polarized because electromagnetic waves are transverse. The direction of polarization is the direction of the electric field vector.

Light is not always polarized, and it can be unpolarized. Unpolarized light is light that has random directions of polarization. This means that the source has oscillations along many planes at the same time (like a light bulb and the Sun).

Plane polarized light can be gotten from unpolarized light using certain crystals like tourmaline or polarized sheets. A Polaroid sheet is made of complicated long molecules aligned parallel to one another. They act as a group of parallel slits to allow one orientation of the polarization to go through nearly unchanged. This direction is known as the transmission axis. A perpendicular polarization is absorbed nearly totally by the sheet.

A Polaroid sheet can be used as a polarizer to give off plane polarized light from unpolarized light. This is true because the only component of light parallel to the axis is transmitted. This sheet can analyze if light is polarized and to figure out the plane of polarization. If you rotate the polarizer, the transmitted light will be at a maximum when the polarization plane is parallel to the polarizer's axis. A minimum will occur if the plane is perpendicular.

Unpolarized light can be converted into components along two mutually perpendicular directions. If unpolarized light is passed through a polarizer, one of the components is eliminated. This means that the intensity of the light is halved. When two polarizers are crossed, unpolarized light can be stopped entirely.

Another way to give off polarized light is from a reflection. If light hits a nonmetallic media at an angle other than the perpendicular, the reflected beam is polarized.

The amount of polarization does depend on the angle. One hundred percent polarization occurs at the polarizing angle. This angle is also known as Brewster's angle. Here, the reflected ray and the transmitted ray make a ninety degree angle.

March 1, 2007:

Today we discussed electric fields and programming our webpages. We also discussed Maxwell's equations and how to figure out the intensity of light. We also used polar coordinates.

February 27, 2007:

Today I researched information about optics. This site is a really good polarized light link, but it is in pdf format. Polarization is a very important topic in polymers, and since I am very interested in studying polymers in chemical engineering, it would be a very good project topic.

February 22, 2007:

Today we discussed how to choose a research topic. It's a really good idea to write down research topic ideas and to get the rest of the details from there. Retarders (also known as wave plates) are used to change the polarized state of the light that travels through it. Also, we discussed Bernard Lyot, who was a polarized light expert in the early twentieth century. We also saw Newton's Rings, which are an interference pattern of dark and light rings caused by light reflection between two surfaces.

February 20, 2007:

Today we worked on how to set up a webpage and how to use a Linux computer system. We also discussed that acrseconds are measured using a circle and that there are 60 arcseconds in an arcminute. This unit is used a lot by astronomers. Also, we learned that a rainbow has a curved shape because of an envelope effect. An envelope is a curve that is made up of the tangent to a family of lines or curves. We also discussed Beer's Law that relates the absorbance of light of distance and concentration. Also, we found out that polymers scatter light in a solution.

February 15, 2007:

Today we talked about Ellipsometer, which measures the index of refraction and the thickness of partially transparent thin films. This device works by shinning a light on a material and catching the reflection. But, for a sample to be used on an ellipsometer, it must have small numbers of well defined layers. Ellipsometry measures the change in polarization of the light that is reflected from the surface of a sample.

Total Internal Reflection occurs when light hits a medium boundary at a steep angle. If the index of refraction is lower on the opposite side of the boundary and no light can pass through, so all of the light is reflected. This is called the critical angle.

February 13, 2007:

So far this semester, we have talked about a lot of the principles of light. Today we discussed Fermat's Principle, which states that light will take the shortest path possible to get to its final destination. In addition, Snell's Law is a formula used to describe the relationship between the angles of incidence and refraction of light passing through a boundary between two different materials, and it was derived from Fermat's Principle.

Edwin Land invented cheap filters for polarizing light, instant polariod photography, and his retinex theory of color vision. Even though he never completed college, he accomplished a lot in his life without a degree.

Maxwell's equations are a group of four equations gathered by James Clerk Maxwell that deal with the behavior of both electric and magnetic fields as well as their interactions with matter. These equations explain how electric charges produce electric fields. Also, the Fresnel Equations describe the behavior of light when moving between materials that have different indexes of refraction. Brewster's angle is found when light travels through two media of differing refractive index and some of the light is reflected at the boundary. At one particular angle of incidence, however, light with one particular polarization cannot be reflected. This angle is called Brewster's angle.

We have discussed buckyballs, their discovery, and how they were named after R. Buckminster Fuller because he had created dome-like structures that looked like them. They had a very interesting discovery. We've also talked about how we can tell that fluorescent lights have mercury in them by looking through diffraction grating glasses. In addition, using two polarized lenses we saw how you can make things disappear if you rotate one lens ninety degrees and if you turn it another ninety degrees it shows a maximum amount of light.

We have worked with focal length, and discovered that you can find a clear reflection of a light source at two distances determined by the focal length. Also, at one point, you can only observe one image. We looked at stresses in plastics as well and how you could tell that a plastic was stressed.



Kristine Horvat
February 2007
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