Nothing immediately obvious from either the PR or SR bottom-stage OSEMs during this time. Ditto the BS and ITM oplevs.

Nothing immediately obvious from distribution amp monitors or LO monitors.

A bit more methodically now: all the OSEM readbacks for DRMI optics, including the IMC mirrors and the input mirrors. No obvious correlation with POP90 fluctuations.

I am tagging detchar in this post. Betsy and I spent some more time looking at sus electronics channels, but nothing jumped out as problematic. (Although I attach the fast current monitors for the beamsplitter penultimate stage: UR looks like it has many fast glitches. I have not looked systematically at other current or voltage monitors on the suspensions.)

Most likely, noise hunting cannot continue until this problem is fixed.

We would greatly appreciate some help from detchar in identifying which sus electronics channels (if any) are suspect.

In this case, data during any of the ISC_LOCK guardian states 101 through 104 is good to look at (these correspond to DRMI locking with arms off resonance). Higher-numbered guardian states will also show this POP90 problem. This problem only started after Tuesday afternoon local time.

I said above that nothing can be seen in the osems, but that is based only on second-trends of the time series. Perhaps something will be revealed in spectrograms, as when we went through this exercise several months before.

Comparing MASTER and NOISEMON spectra from a nominal low noise time on Feb 3 with Jan 10, the most suspicious change is SR2 M3 UL. Previously, this noisemon looked similar to the other quadrants, but with an extra forest of lines above 100 Hz. Now, the noisemon looks dead.

Attached are spectra of the UR quadrant, showing that it hasn't changed, and spectra of SR2 M3 UL, showing that something has failed - either the noisemon or the driver. Blue traces are from Feb 3 during a nominal low noise time, and red are a reference from science time on Jan 10. I'm also attaching two PDFs - the first is spectra of master and noisemon channels, and their coherence, from the reference time. The second is the same from the current bad time. Ignore the empty plots, they happen if the drive is zero. Also, it seems like the BS M2 noisemon channels have gone missing since the end of the run, so I had to take them out of the configuration. Also, I took out the ITMs, but I should probably check those too.