It looks like we just lost lock due to a PI ringup at about 10.4 kHz.
The IFO was pretty nicely thermalized at 50W, and then I had taken steps up to 52W and then 54W. We'd been sitting at 54W for about 23 minutes. A minute or so before the lockloss the verbal alarms brought DCPD saturations to our attention, and DARM started to look like it had saturations. Interestingly, with the DCPDs saturating, the DARM spectrum was showing an apparent improvement in shot noise. This is certainly unphysical, but we're not really sure why a saturation at high freq would cause the noise to look better in that way.
Anyhow, we may need to look at what optic that was, and hopefully our plan of turning on some common ITM ring heaters will help keep that mode from having gain.
Georgia found some useful past alogs:
2019: 10.43kHz mode: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=50209
2021, after AMDs, but with new ITMY, 14kHz mode (so not our today freq): https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=58779
Here's a zoomed in spectrum. The PI is the same mode as we saw in 2019: 10.43 kHz on ETMY, so if we want we can tune the ETMY ring heater to try to dodge this guy.
We also seem to have lost lock from this peak last night at 05:37UTC. Screen shots attached. Jenne is investigating whether this is preventing us from locking now.
