Tuesday, January 24, 2006

Week of 1-16-2006

The following project tasks were completed this week:

Followed up with Boulder Nonlinear Systems regarding thier XT and TS shutter systems. Looking at the Bigelow paper, it was found that a maximum carrier modulation frequency of 250Hz is necessary for super luminal propagation. Was put in contact with Kipp Buchart, a solutions engineer at BNS. According to Kipp, BNS shutters elicit a nonlinear response with a linear drive voltage, so to properly operate the shutter for our applications a normal sinusoidal function generator will need to integrate a nonlinear transfer function before driving the shutter. The main issue with using the exisitng BNS shutters is that they elicit a 25 ms total response time corresponding to a modulation frequency of 40 Hz. This will however be sufficient for a signal frequency to be modulated on top of the 250Hz carrier frequency. It was decided between Dr. Blair and myself that this will be used for our low frequency signal modulation frequencies, and that Dr. Blair will speak to the BNS representatives the week of 11-23 at a conference he will be attending in San Jose California.

I also discovered that sinusoidal modulation can be achieved using the original square chopper wheel. This is achieved by taking the chopper wheel with chopping slits just wider than the beam diameter and setting the wheel at an angle such that the edges of the beam are barely clipped by the sides of the chopper wheel. When the wheel spins, an approximation of a sinusoid is achieved. This simple method will be very sufficient to achieve our modulation needs.

This method was implmented in the setup late Friday, and will be tested the following week.

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