Monday, March 06, 2006

Week of 2-27.06

The following specific project tasks were completed this week:

After further characterization of the LC cross polarizer variable attenuator device, the following observations were made this week:
- The device works best at around 40 - 60 Hz, and exhibits a very close sinusoidal approximation at this frequency. There is however, a moderate DC shift in the dectector levels at this frequency.
- A DC level shift in the detector signal is present regardless of the driving signal frequency. This shift however increases with increasing modulation frequency. The amplitude modulation riding this DC shift also decreases with increasing frequency, however, it remails sinusoidal.
- At low frequencies (5-10Hz), the device does not produce a very accurate sinusoidal approximation. The output exhibits a signal which has peaks which are roughly sinusoidal with some high frequency nosie, and valleys which are roughly flat. Basically a square signal with a rounded response for the high level of the square wave signal. This is essentially the modulation response seen last week. This response (especially the high frequency noise) can be improved by using a filter and avoiding detector saturation.
From looking at the Bigelow, Lepeshkin, and Boyd papers, for ultraslow propagation, the spectrial hole required in ruby is 36 Hz and for alexandrite is 8.4 Hz. Ultra-fast propagation in alexandrite requries a spectrail antihole of 612Hz. To achieve both superluminal and ultraslow propagation requires frequencies of around 250Hz and less, with ultraslow propagation possible at the lower frequencies in this range (50Hz) Looking at what I've been able to do with the LC cell and what the papers indicate is needed, it looks like for ultraslow propagation in ruby, the LC cells will work well. Something faster may be needed for alexandrite and ultrafast propagation.


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