Stefan, Evan

We made another attempt at using 90 MHz to center WFS AS B.

This time we turned up the whitening gain to 45 dB, which gave a healthy number of counts on each quadrant. We then redid our dark offsets, which were significant at this whitening gain. [We actually redid the dark offsets for all the REFL and AS WFS signals using the script in the userapps repo.]

Then in DRMI, we phased each quadrant to put most of the power in I. At this point we saw that the centering signals provided by these 90 MHz quadrants (pitch and yaw) were slightly different than the dc centering signals for AS B, so we switched the centering over to these signals (a relative gain of −0.003 is required between these 90 MHz signals and the dc signals). Things seemed fine in DRMI (the sideband buildups all changed slightly, but it was hard to say whether they were better or worse), but when we tried the CARM reduction sequence, the new centering ran away on the DARM WFS step.

So instead, we went to full lock at 2 W with the old centering scheme and switched over again to the new 90 MHz AS B centering. Things again seemed fine.

We weren't quite sure what to do about the BS/SRM matrix elements. In the end we tried using AS B 36 I&Q only to control these loops (i.e., no mixture with AS A 36), and this was fine at 2 W, but we lost lock immediately when trying to power up.