camilla.compton@LIGO.ORG - posted 16:58, Thursday 06 August 2026 (91436)
HAM7 Work - Thursday 6th August - ZM4 and ZM5 realigned after preload and chassis change, A:L2 Aperture removed, OPOS rebalanced.
Sheila, Ryan S, Camilla, Rahul
This morning Fil and Rahul go the ZM5 chassis working, 91431. Ryan checked the Strain gauge resistors didn't need adjusting after ZM4 preload adjustment 91416. This afternoon we used the iris at ZM5 and irises on SQZT7 to realign ZM4 and ZM5 after this chassis swap and ZM4 offload. New ZM4 ans ZM5 settings: attached.
This morning Sheila and I checked more power budgets using craning over the OPOS. Sheila has the numbers but we convinced ourselves that the aperture at A:L2 is causing us to lose up to 2% power. But the aperture at B:L1 we are not clipping as we could not increase the power through it by moving FC1 (stepped ~20urad and then took the mean of 10s of data on the Thorlabs power meter).
This afternoon, after restoring the ZM4 and ZM5 alignment, we locked the OPOS suspension, removed A:L2 using the M2 screws in the translation stage and removed the A:L2 aperture. This aperture is dumping incorrectly polarized SQZ light, not IFO light so removing it will not cause any IFO backscatter. On replacing the aperture we added a small weight just upstream of A:L2, photo, to recenter the OPOS balancing, photos attached of the three views.
We still need to run OPOS health checks.
The light getting to SQZT7 was still clipping, by eye around SFI2, so Ryan and I then adjusted ZM2 (to center on ZM3 iris) and ZM3 (to retroreflect the beam). Sliders attached. Strangely, we get the unclipped beam when ZM3 was ~100urad off in YAW than what we thought the best retroreflecting centering was. Though with this unclipped setting we still cannot see that the beam isn't retroreflecting without offsetting in Pitch. We left it in this unclipped setting. The retro refection could be double checked.
Images attached to this report
