Jeff, Oli

We were a bit unsure yesterday about the OPO but after some more measurements today I've confirmed that it is looking good. It still doesn't look like it did in 2022, but it works for us.

After some cable redressing last week the OPO was looking a lot better (88921), and then some further redressing was done (88957), which didn't seem to help, but at least didn't make Yaw worse. Those measurements were all taken with the ISI Locked. Yesterday I took what were supposed to be closeout measurements with the ISI now unlocked and DAMPED, but those measurements looked different from last week's, and not in a good way. There were two sets of measurements taken yesterday, one with the OPO damping all off (2026-02-03 1815UTC), and one where the DOF being measured was turned off, but the other DOFs were left damping (aka semi-off) (2026-02-03 1730UTC). Both measurement sets looked about the same besides a small increase in the highest frequency peak, but nowhere near the height it had been at last week(regular, zoomed).

In both sets of measurements, the lowest- and highest-frequency peaks (cross-coupling from T and V, respectively) were much smaller than they had been last week (last week we had thought the lowest peak had been split off from the main Yaw peak, but it was actually a shifted T cross-coupling). This was unexpected. The only (known) difference between last week's measurements and these two sets is the difference in the ISI, Locked vs Unlocked and DAMPED.

We decided to look at previous OPO measurements(regular, zoomed, txt explaining timeline from Jeff) taken with the ISI Locked, DAMPED, and ISOLATED, and found that the OPO resonances go down in Q when going from Locked to DAMPED. It also looks like once the ISI is ISOLATED, the resonances will rise back up(better zoom in). This could make sense as to why we're only seeing changes in the T and V resonances since the ISI moving side to side or up and down while in DAMPING would couple more directly into the OPO than when the ISI rotates.

The only way to confirm this idea was to take more measurements while the ISI was either Locked again or ISOLATED. Since yesterday afternoon the ISI had to be Locked again, I was able to take some measurements this morning(2026-02-04 1545UTC(all damping off), 2026-02-04 1630UTC(damping semi-off)), and they confirmed that the OPO looks like it did last week(regular, zoomed). So we're pretty sure once the ISI is back to ISOLATED it'll look like it did when the ISI was Locked earlier today and last week.

Yesterday's Measurements
- ISI Unlocked and DAMPED
2026-02-03 1730UTC
- OPO M1 DAMP all ON EXCEPT for DOF we are measuring (Semi-Off)
Data
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Data/2026-02-03_1730_H1SUSOPO_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz.xml
r12868
Results
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Results/2026-02-03_1730_H1SUSOPO_M1_ALL_TFs.pdf
r12869

2026-02-03 1815UTC
- OPO M1 DAMP all OFF
Data
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Data/2026-02-03_1815_H1SUSOPO_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz.xml
r12868
Results
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Results/2026-02-03_1815_H1SUSOPO_M1_ALL_TFs.pdf
r12869

Today's Measurements
- ISI Locked
2026-02-04 1545UTC
- OPO M1 DAMP all OFF
Data
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Data/2026-02-04_1545_H1SUSOPO_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz.xml
r12874
Results
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Results/2026-02-04_1545_H1SUSOPO_M1_ALL_TFs.pdf
r12876

2026-02-04 1630UTC
- OPO M1 DAMP all ON EXCEPT for DOF we are measuring (Semi-Off)
Data
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Data/2026-02-04_1630_H1SUSOPO_M1_WhiteNoise_{L,T,V,R,P,Y}_0p02to50Hz.xml
r12878
Results
/ligo/svncommon/SusSVN/sus/trunk/OPOS/H1/OPO/SAGM1/Results/2026-02-04_1630_H1SUSOPO_M1_ALL_TFs.pdf
r12877

Comparison plots
2022 vs last week vs yesterday
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_StillPossibleIssue_ALL_TFs.pdf
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_StillPossibleIssue_ALL_ZOOMED_TFs.pdf
r12872

ISI Locked v Damped v Isolated
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_MaybeMysterySolved_ALL_TFs.pdf
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_MaybeMysterySolved_ALL_ZOOMED_TFs.pdf
r12871

Everything looking good today
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_LookingGood_ALL_TFs.pdf
/ligo/svncommon/SusSVN/sus/trunk/OPOS/Common/Data/alloposs_2026-02-03_H1SUSOPO_LookingGood_ALL_ZOOMED_TFs.pdf
r12887