Jenne, Naoki, Brina, Sheila
We put some offsets into the AS WFS loops, to check test if offsets in these loops caused by the OM2 change might be responsible for the change in jitter coupling that we see with heating of OM2. We didn't see much improvement in the jitter coupling from adding pitch offsets to AS 72Q (SRM) or AS 36Q (MICH), but yaw moves made a big difference in the jitter coupling, as well as the low frequency noise.
Times with om2 cold today :
- sqz off, AS72 Q Y offset +120 counts 21:49:17- 22:00:00 UTC (SRM yaw)
- sqz on, AS 36 Q yaw 50,000 22:22:00-22:32 UTC (BS yaw)
- no offsets, sqz on, 20:00 UTC (calibration measurement time)
Gabriele ran a bruco for the first time here. He also notes that the low frequency at this time looks like it could be scattered light.
We are leaving offsets in AS 36Q yaw +35000, no offsets in AS72.
A spectrogram of DARM during the time used for the BruCo scan. It looks to me like it's scattered light, with clear bumps at 13, 18, 23 and 28 Hz
A higher resolution (0.1 Hz) BruCo scan is available here: https://ldas-jobs.ligo-wa.caltech.edu/~gabriele.vajente/bruco_DARM_1373320218_HR/
Here are a few other comparisons, but using GDS-CALIB_STRAIN_NOLINES so that we can see things, including the effect of things (like optical gain) that affect the calibration.
The teal is from 28 June 2023 08:00:00 UTC, when OM2 was hot.
Blue is from 13 July 2023 20:00:00 UTC, so basically the same situation we had overnight all night, OM2 cold and no ASC offsets. (Same time as the black traces in Sheila's plots above). Here, the jitter peak around 120 Hz is very high, and there are several other peaks throughout the bucket that could be jitter-related.
Red is as we are now, 13 July 2023 23:02:00 UTC, with a cold OM2 and AS A 36 Q yaw offset of +35000 counts. The 120 Hz jitter peak is about the same, or maybe better than while OM2 was hot. Since kappa_c is 1, our optical gain is better than the hot OM2 state, which improves our high frequency sensitivity. Also, the sensitivity below 30 Hz seems quite good. However, the sensitivity from 30 Hz - 100 Hz isn't great, and it could be related to scattered light, as Gabriele is pointing out. We should consider checking things like the alignment of the compensation plates with this overall IFO alignment.
Also attached is the SDF Observe being accepted with +35000 counts for AS36Q yaw and offset on. Note that the TRAMP is saved as 10 sec, but I'm putting it in to the guardian as 30 sec, so we should accept a 30 sec tramp next time we're out of Observe.
I have modified the ADS_TO_CAMERAS state in ISC_LOCK to also turn on this offset. I haven't loaded it since we're in Observing. I've only "checked the syntax" by confirming that I can open the graph. I've written it assuming that SDF revert will turn off the offset and set it to zero.
