[Jennie, Evan, Gabriele]
We tried again to move the input beam pointing in-lock, similarly to what was done in 76359.
First we moved IM1 and IM3 in pitch, looking at IM4_TRANS and POP_LF. We could increase the power in IM4, and we moved until we reached a maximum in POP_LF. Half way during the test we switched back to ADS from cameras, but it turns out that the PRM ADS was moving in the wrong direction. We went back to camera servos (restoring the original, correct offsets) and helped PRM along to speed up the camera servo convergence.
When we reached this maximum of POP_LF by moving pitch IM1 and IM3, we checked DARM: there was more noise in DARM at low frequency and around 100 Hz, the range was lower, but coherence with jitter was unchanged. Evan tried to improve things by tuning the SQZ, without luck.
We then moved to yaw, and we could improve IM4 and POP_LF further. Unfortunately we lost lock during the test. We don't believe we caused the lock loss.
The change in input beam alignment had a good effect on the optical gain, KAPPA_C increased by 2% (yaw being the most effective direction). For comparison IM4_TRANS improved by 6.6%, POP_LF improved by 2.8%
The arm power also increased proportionally to LSC-POP and ASC-POP. I think this means that moving the input pointing we were fixing some clipping in the PRC. It's worth repeating the test: we could go back to the pitch position we found (by moving IM1, IM3 with a long ramp, and also moving PRM to the new value, and maybe also IM4?). From there we can restart the yaw motion, which seemed promising.
I reverted the alignment changes to IM1, IM3 and PRM. See attched images of the SDFs for SUSPRM and SUSIM models.
For future reference, here are the moves we did (in SUS offset sliders) or loops did for us (in M1 DAMP IN units, should be the same as sliders)
| Optic (pitch) | Initial value | Final value | Change |
| IM1 (us moving) | 7794 | 2900 | -4894 |
| IM3 (us moving) | -7576 | -5376 | +2200 |
| IM4 (loop) | -2862 | -2731 | +131 |
| PRM (loop helped by us) | -1314 | -1132 | +182 |
| PR2 (loop) | -484 | -516 | -32 |
| PR3 | none | ||
| BS | none |