During breaks in the locking action this week, I have tuned up the OMC alignment loops that use OM3 and the OMC suspension to align the beam into the cavity.  These loops are now stable; I've measured the OLTFs and everything looks robust.

I also fixed the dither alignment loops, though a combination of adjusting (audio) demod phases, moving frequencies around to avoid peaks in the intensity noise, and lowpass filters to get rid of the high-frequency junk.  These might need some attention later, we should change the dither frequencies to match L1.

The first plot attached is a figure of the noise suppression with the AS WFS DC centering and the OMC ASC turned on.  Top panel is beam jitter on the AS WFS, lower panel is beam jitter into the OMC.  References 0-4 are with no loops closed, 8-11 are with the AS WFS centering loops closed, and the current traces are after the OMC ASC loops are closed.  The AS WFS centering is fairly high gain, something like 3Hz, we could turn this down.  The OMC ASC loops are around 1-2Hz UGF, when the QPD signals are used.  (The dither loops are much slower.)

Second plot attached is an example of an OMC ASC loop transfer function.  The inversion of the OMCS plant leaves a broad peak, but there's plenty of phase margin.

Third plot attached is the new output matrix, there were a few sign errors in the picture from the earlier post.

I have updated the OMC safe.snap file with the new filters, gains, etc.

This evening I also checked the balance of the OMC DCPDs, using an excitation in the cavity length, and changing the DCPD_BALANCE slider to minimize the peak height in the nullstream channel.  I found that an exact 50-50 split was the best choice.  Might need to check this again with a variety of amplitudes and frequencies, the result is seems a little too perfect.