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.
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