Motivation
During this locking session, we've seen that beam jitter is limiting DARM worse than in March 2025.
We've also seen it's worse upstream, in e.g. IMC REFL DC (alog 84809).
We've been skipping closing the ISS SECONDLOOP while locking, because we have evidence that the witnessed beam jitter noise on the ISS array now is much higher than in the past (See PDF 1 from March 2025 versus now: this plot from alog 84805).

What we did
We picoed on the ISS array to a very new position, following the instructions from alog 63431.
Our goal was to maximize the power on the ISS array PDs, and to see if by aligning onto the PDs better, if we could reduce the observed intensity fluctuations on the ISS array PDs as well as in DARM.
We did all of this with the SECONDLOOP open.

Results
We were successful in picoing to get new higher powers on the PDs.
PNG 1 shows how far we moved on the HAM2 + oplev picomotor 8, -150 in X and +320 in Y.
PNG 2 shows how much power we gained on the PD array during picoing.

We were successful in getting lower beam-jitter-induced intensity noise on the PD array as well.
PDF 2 is the PSDs from every ISS array PD, and should be compared to alog 84805.
The IMC ASC and beam jitter peaks are largely reduced in every PD now.

We ended up realigned onto the ISS QPD, at PIT = -0.8 and YAW = 0.17.
We started at PIT = -0.97 and YAW = -0.63.
ISS QPD SEG3 is no longer saturating, but SEG4 is now VERY close to saturation, so we did not really solve that problem.

Discussion
We did not really finish picoing because we started the Simulines calibration script which seem to have killed the lock twice now.  
I think the place we are leaving the alignment should be better for locking and for closing the ISS SECONDLOOP.

We as usual saw the powers on the PDs moving differentially (some going up, while others go down).  
I prioritized maximizing the power/eliminating the noise on the in-loop PDs 1-4.  

Matt Todd will post a comparison of DARM before and after picoing on the ISS array.
We should not have expected an improvement because we know our beam jitter is coming from upstream, but it's possible we improved something at 410 Hz.  
It should also just be nonstationary noise or thermalization. 

I recommend altering the IMC alignment to help ameliorate our beam jitter woes.  
We have evidence from IM4 TRANS and IMC WFS DC that our input alignment is altered slightly, and the IMC REFL camera lately has been looking like an big S.
It may be time for walking the IMC alignment, either with DOF4 steps or MC2 QPD offsets. 

Robert also suggests that the turbo pumps running next to HAM1 could be a source of our elevated beam jitter peaks.