We looked at some filter cavity detunings and slightly varied the generated squeezing level, to see if we could at all change the noise around 70-100 Hz. It's not entirely clear what's going on, no huge obvious changes, but perhaps subtle ones. At least, even at low frequencies < 100 Hz, it seems like higher NLG is slightly better, and that moving the FC detuning to -25 Hz is not obviously worse. To start, I just tried moving FC detuning up/down 5 Hz, and rotating sqz angle to see if anything was better, see the trends of the moves here.
From the screenshot, red + cyan are from hot om2 last time on 6/28. Other traces are from the recent heating of OM2; the recent no-sqz seems to have other injections going on at the same time. There may be a slight difference between brown FDS (before moving anything), the yellow FDS (moving FC detuning from -30 Hz to -25 Hz, and slightly increasing NLG), and the dark blue FDS (less NLG, same FC - 25Hz detuning, different sqz angle apparently).
For now, I have left the squeezer in the "yellow" configuration from above (previously we were in "brown" configuration). Differences are 90uW OPO trans (compared to 85uW), and filter cavity detuning at -25 Hz (instead of -30 Hz). Squeeze angle is the same, 145 deg. In SDF, I've accepted the FC detuning change, and OPO temp change. I think the difference might be marginal at best, but interested how it goes when IFO is thermalized. Screenshot showing ~2 hours into lock in the black trace here, looks similar to the yellow.
