Monday, February 20, 2006

Week of 2-13-06

The following project tasks were completed this week:

The LC retarder was obtained at the end of last week, and initial testing was started this week. To first confirm proper device operation, the LC device was placed between two polymer sheet polarizers, and a sinusoidal voltage was applied to the wires attached to the control electrodes, which I soldered to the device. A sinusoidal response in transmission intensity through the device was seen. It was found that to achieve maximum contrast, the device required approximately a +/- 4 V drive voltage.

Testing of the device was then performed in the actual setup using the Argon laser. This utilized the LC retarder/cross polarizer device, the Argon laser, a function generator, a Newport optical power detector, and an oscilloscope. It was seen that with a sinusoidal drive voltage, the transmission intensity was approximately sinusoidal, however, the duration of the sinusoid peaks was slightly shorter than the valleys. I spoke with Gary Sharp at Colorlink about this problem, and we deduced that it was because the LC device has a faster ‘on’ time than ‘off’ time and this would cause this sort of skewed response. To fix this problem, a sawtooth wave was applied with the same voltage levels. It was observed that this fixed the skewed sinusoid that was observed before. Using this drive signal, modulation frequencies as low as 3 Hz and as high as 100Hz were accurately achieved.

This modulation setup was integrated into the final experimental setup, and final testing of super-luminal and slow light propagation is now possible.

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