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Apparatus
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Laser: a 20 mW Helium Neon laser of 632.8nm wavelength; Lens: 75mm plano-convex lens
The light scattered at 90 degrees passed through a piece of tape with a 1mm hole near the surface of the cell. This was to limit # of Coherence Areas by reducing scattered beam size. The second iris controlled area of light incident on photo diode. Our set up gave us about 7602 coherence areas.
The photo diode was connected to a current preamplifier( SR570) which amplified the current set to one microamp per volt.
This amplified current was converted into a voltage signal and amplified using a voltage amplifier( SR560) with a gain of 10^4.
A Labview code recording 2000 samples at 2000 Hz acquired data for 200 seconds for each trial.
Additionally, a function generator and an attenuator were used to create a noise signal for initial calibration measurements to determine the amplifier noise.
In order to limit the background effects, the second iris and photo diode were covered using an aluminum box that was painted black. It had a small hole through which the scattered beam passed.
The lights in the room were turned off and the amplifiers ran in battery mode in order to limit additional background effects. It was determined that our computer monitor being on did not affect our results, although the monitor did not face the apparatus.
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