Sheila, Camilla, Jennie W, Keita remote
Stefan and Daniel suspect that our excess noise around 100 Hz might be due to intensity noise, and we did have a large shift in alignment of the beam transmitted through IM4 (76291) 76241. I moved pico 1, first to center the beam on the ISS QPD, which made the power on the ISS array PDs drop, and didn't improve the spectrum of the ISS Sum inner or outer channels (we did this with the loop open). We reverted this, then looked at the QPD position in O4a when we had 60W input power, went to 60W input power and pico'd to bring the beam to the same location as O4a. This also didn't improve the spectrum, so we brought the pico back to where we started.
Sheila asked me to compare the ISS second loop outputs with from our recent NLN lock last night to that during O4a. The spectra doesn't show much difference in the noise (top left plot shows Jan 14th lock in cyan and yellow, last night's one in pink and brown).
The other three plots shows the coherence of ISS output with all three GS13s on the HAM2 optical table. There only seems to be coherence at the power lines.
So maybe the ISS is not causing intensity noise to couple into DARM differently pre and post vent.
Images 2 and 3 attached shows the ndscope fro all channels I used around the two times I took spectra.
Time 1 = 2024-01-14 22:05:27 UTC
Time 2 = 2024-03-12 12:53:24 UTC
Channels for ISS:
H1:PSL-ISS_SECONDLOOP_PDSUMINNER_OUT_DQ
H1:PSL-ISS_SECONDLOOP_PDSUMOUTER_OUT_DQ
Channels for GS13s:
H1:ISI-HAM2_BLND_GS13X_IN1_DQ
H1:ISI-HAM2_BLND_GS13Y_IN1_DQ
H1:ISI-HAM2_BLND_GS13Z_IN1_DQ
I looked at the pointing of the IMs and MCs from the start of a lock 16th Janary to now. As previously found, nothing seems to have changed much, IM1 P changed by ~100 counts, more than the other IMs, but it's unclear what these counts are calibrated to.
