Moon Limb & Nilus Klingel
Submitted to the 2005 Siemens-Westinghouse and 2006 LISEF Competitions
READ THE ACTUAL PAPER! [ SIEMENS.PDF ] (PDF, 586 KB)
This experiment was conducted several weeks after it had been suggested to me, and was to a certain extent the impetus for this project-proper getting under way (Before I had conducted this experiment, I was very lost in the confusing decision on what my 'real project' would be.) This experiment, while not particularly successful, helped focus myself on this line of experimentation.
Essentially, the project's point was to see if there was some sort of change in an interferogram when a piece of cellophane was rotated in one arm of a Michelson interferometer, perpendicular to the beam. We had wondered if cellophane was a half wave plate, and decided to experiment to Ăsee if the pattern would 'breath' in an out as the cellophane was rotated, passing the beam through different optical axes.
The setup consisted of a michelson interferometer with a piece of cellophane mounted on a rotator in one of the interferometer's arms. In place of a typical viewing screen, a photodetector was set up, preceeded by an aperture, so as to allow only the central point of the interferogram to hit the photodetector. With this set up, we could detect changes in the interferogram as it expanded (or contracted) as the central region would go from light to dark.
The data collection took somewhere around 2 hours, as the cellophane was rotated in 72 10 degree intervals. To ensure that the photodetector's reading wasn't thrown off by fluctuations, each reading was averaged over a period of 1 minute. The data collected lead to the following graph:
The blue points represent the data taken, and the red line is a line-of-best-fit that Dr. Noé and I attempted to fit over the data in a search for some kind of trend. As you can see, the data show no notable trend.
We decided that the data may have been thrown off by drifts
in the room, or by the averaging function of the multimeter. Then at a
lunchtime epiphany, we realized that inserting a half wave plate (which we
believed cellophane was) into an arm of a Michelson interferometer meant
that the beam passed through it twice; once headed to the mirror, and once
on its way back. This had the total effect of a full wave plate, which
does nothing. With this mystery solved, we closed the book on this
Graphs of (left) Intensity of light passing through a polarizer and a
rotating analyzer, and (right) Intensity of light passing through a
polarizer, rotating piece of cellophane, and stationary analyzer.
Graph of Intensity of light passing through a Linear
Polarizer, a stationary piece of cellophane, and a rotating
analyzer. Colors represent relative angle of cellophane to the
Linear Polarizer; dark red is 0°, red-orange is 15°,
green is 30° and blue is 45°.