Today, Sheila and I followed up on this, and the results are a bit confusing, but somewhat promising.

To start, Sheila reran the "brontosaurus plot" measurement, where FIS is injected to help determine the SRCL offset. She reports this work here.

While she changed the SRCL offset, I once again monitored the AS RF72 and POP X signals. As Sheila changed the SRCL offset, the offset in POPX did change the same way as I saw yesterday, which is not that surprising.

Then, when Sheila set the SRCL offset to zero, I tried opening the SRC1 loop and moving SRM around. The first thing I noticed is that the calibration I calculated yesterday seems bad, since I was adjusting the SRM yaw by 11 urad (according to the slider calibration), but the change in the POP X yaw offset corresponded to less than 1 urad (according to my measured calibration from yesterday).

I moved yaw in only one direction, with the goal of seeing if I could reduce the POP X yaw offset. However, I gave up after 11 urad because it didn't seem to be doing much at all except to small effect on POP X yaw.

Next, I tried moving SRM in pitch. I went the positive direction, and Sheila and I immediately saw the buildups get worse, so then I went the other way and the buildups got better! This corresponded to a 20 urad change in SRM pitch, according to the alignment slider. The change in the POP X pitch offset was minimal.

We also saw kappa C increase quite a bit, almost too good to be true, so we didn't trust the value since we had a large SRCL detuning at the time. Sheila did see that the change in the SRM pitch had an effect on the squeezing as well.

However, Sheila then determined a better SRCL offset of -382, so we went there, and the kappa C leveled off to 1.02, which was better than our current nominal value of 1. This seemed to hold. Then, I stepped the SRM pitch offset back to the starting alignment and the buildups decreased and kappa C went back to 1.

Following the buildups, there seems to be a better alignment of the SRM in pitch. At this time it seems like yaw has no effect, but I only moved in one direction. I think that, whatever the SRCL offset is, we should move the SRM around in pitch and yaw and see if there is an improvement to be found in the buildups. My current hypothesis is that the RF72 dark offsets are creating some alignment offset in the SRC. After we find a good SRM alignment position, we can recheck the SRCL offset, hopefully with both a squeezing measurement and a sensing function.

We should also probably check the whitening on RF72, maybe next Tuesday.

These results are making me think that probably POP X Q would not make a good signal for SRC alignment, since it is dominated by the SRCL offset.

The first ndscope attached are showing the behavior of the POP X and RF72 signals while changing SRM alignment. The second shows the buildups and kappa C when changing SRM pitch and SRCL offset from 0 to -382.

Plot attached, we think that the SQZ is worse at NLG 10 that the other NLGs and we are considering running with NLG = 14.

Here's a fit of Camilla's data, it shows that our OPO threshold has increased compared to 83070, and we still have the same efficiency for squeezing, which implies 6% unexplained loss, which hasn't been fixed by moving the crystal. 

This plot was made using this script

We decided that an OPO TRANS setpoint of 105uW for an NLG of 14 gave us slightly better squeezing, see attached BLRMS. Leaving this in.

If the Operators have any issues keeping the OPO locked at this higher output power, they could lower it slightly following the instructions in 70050 to drop it down to 100uW or 95uW.

18:48 Back to NOMINAL_LOW_NOISE

Within the same ~15 seconds of the lockloss, we turned the CO2 powers down form 1.7W each to 0.9W each. In the hope of doing the thermalization tests we tried last week 85238.

We checked the lockloss today and LSC channels at the time last week we turned the CO2s down and see no glitches corresponding with the CO2 waveplate (out of vac) change, we think the lockloss was unrelated.

NOTE that PT114 is currently disabled in VACSTAT, this cold-cathode is yet to "catch" following yesterday's restart of h0vacly

The control room FOM caqtdm version of the vacuum overview was upgraded and nuc22 rebooted at 10:35

Looking at the lockloss from last night (2025-06-25 11:02 UTC - note that the 'refined lockloss time' is one whole second early than the actual lockloss time), it's immediately clear that we lost lock due to a quick ringup, but it is unclear where that ringup came from or what frequency it was actually at. We can see an 8Hz oscillation in DARM one second before the lockloss, but looking at the LSC channels, SRCL sees a 1.5 Hz oscillation right before the lockloss, and PRCL has a 4.5 Hz oscillation (although the PRCL oscillation could be unrelated, although it does look like it grows a bit larger). In the ASC channels, MICH P OUT has a ringup at ~3.8 Hz in that last second, and some of the other ASC channels look like they maybe also have some sort of excursion right before the lockloss.

With regards to ENGAGE_ASC_FOR_FULL_IFO, the three locks that we've had after the adjustment made yesterday have made the state take an average of 4.5 minutes to get through. Before making this change, it was taking us an average of 8.5 minutes (looking at the four locks before this change), so this has made a big improvement for this state!

However, it looks like the main reason why this state still takes a pretty long time compared to most other states is because it's still needing to wait a long time for the PIT3 and YAW3 ADS to converge (ndscope). Here's the log from this last time that we went through ENGAGE_ASC and you can see that most of the time is waiting for ADS. The actual wait timers in there are only 50 seconds of waiting, so the rest of the wait timers (the one second timers) are just from the convergence checker.

I updated the POP A yaw offset so that PRC1 in DRMI will bring the PRM closer to the full lock point and hopefully make convergence in this state faster.

I ran two brucos, one on NOLINES and one on CLEAN.

bruco NOLINES

bruco CLEAN

Overall, the message of Tony's alog is that, relative to our best range, we have lost 10 Mpc by the time we reach 100 Hz, and an additional 5 Mpc by the time we reach 1 kHz. The brucos above show a lot of low level coherence with: MICH, SRCL, PRCL, REFL RIN. There is a chance that making additional improvements to the feedforward can help. Right now it's hard to tell how many Mpc that gets us back, but it's where we should start.

I made a range comparison with a time form last night when we got up to 155Mpc (Jun 25, 2025 05:07:30 UTC (1434863268)) and compared it to a time of good range before the vent, Apr 01, 2025 03:05:42 UTC (1427511960). Here's the range comparison.

This is interesting because it indicates that the range loss at low frequency in DARM now versus right before the vent is much smaller, only 3 Mpc. But looking back to our best range in April 2024, there is even more loss in sensitivity at low frequency.