7.12.10 [2]

Wow, 2 posts within 24 hours. This is what happens when you can't nail down consistent sleep patterns.

Advisor was intrigued by the comparison of the velocity estimates (see plot in previous post). Particularly, both lines have almost the same shape, and appear to only differ by the average slope, ie the velocity. I proposed that this is because the poke matrix doesn't account for the change in the beam size that's roughly proportional to the norm of the command vector. Relatively small perturbations are used to estimate the poke matrix, so the beam diameter is actually smaller for general random commands. A particular phase profile enters and exits the DM surface in the same time for either case, so if the actual beam diameter is smaller it means that the phase traverses fewer pixels for a given time period, ergo resulting in a lower velocity estimate.

I have no idea if that makes any sense since its around 2AM. In any case, its not clear there's anything I can really do about it other than estimate some correcting scale factor and apply that to every command sequence. Its also not clear if any of this velocity estimation stuff will make it in a paper or my dissertation, so I'm not sure its worth devoting my entire life to something that's basically a sideshow to the main event.

Anyway, tomorrow (today), I'd like to ignore this discrepancy for now and look at applying phases at twice to rate to see if I can measure twice the velocity. I plan on doing this by using the same sequence of phases from the SS model, but just applying every other command.

I'm also making some (theoretical) progress on implementing an optimal FIR filter in the actual AO experiment. I still have to think about what it means to do the calculation in the multi-channel case.