4.28.11

Holy shit this thing is out of date now. That's what happens when you get busy [not]working.

Since February I've gotten things working relatively well, with one major realignment along the way to remove some barrel distortion that (I think) was caused by the beam getting too close to the edge of a lens. I've also placed L4 on a stage to mitigate the bias WF rather than manually moving L2. Relatively speaking, this lens only needs to be moved a few mm to correct for the DM bias, and using a stage keeps everything in alignment. True the imaging planes of all the following components changes, but so far that effect seems to be negligible. One boring day I'll write a long post about my thoughts on the alignment procedure.

I've also installed plane mirrors, which bypass the DMs, to create a absolute reference WF that I used to generate a SHWFS reference grid. With this latest setup I'm usually able to get the actual beam (w/ DMs) pretty close to this original position.

At the moment I've settled on using the number of modes to control the saturation problem, which seems to be less of an issue than before. Amazingly, the system seems robust enough that I can actually use the "optimal" integrator gain of 0.5 as determined from a sensitivity Bode plot, nearly an order of magnitude larger than the gain I was using before. As a result, the difference in performance between the integrator and LTI controller isn't nearly as wide as before, but now I at least have a reasonable "best case" classical controller to compare it to.

Much more has happened, but in a nutshell I spent today writing some code to compute the encircled energy. I'm still exploring just how much improvement I can eek out of the LTI controller, so tomorrow and next week I plan to experiment with progressively stronger disturbance scales and control modes to find what I can get away with.