Sheila, Rahul
We got back into HAM7 for beam alignment work after ZM5 was repaired and, up & running. Listed below are the things we did to check and improve the alignment in HAM7 chamber and also on the SQZT7 irises.
1. Checked the incoming beam on ZM5 from ZM4, found it to be off in yaw by few mm - hence we translated ZM5 (pushing it in the direction towards SQZT7 table) to center the beam on the PSAMS.
2. Checked the reflected beam from ZM5 on the iris (which Camilla had set last week) - it was off in Yaw and was too high as well. Hence, I mechanically adjusted the pitch and yawed the suspension cage to center the beam on the iris. Sheila then checked the beam on the two irises in SQZT7. Using sliders we were able to center it nicely on the two irises, however several times while doing so we were eating up on DAC output. Hence iteratively we were using sliders and mechanically offloading Pitch/Yaw by adjusting the pitch adjuster or yawing the suspension cage.
3. Sheila also used ZM4 sliders to fine tune the alignment on the irises on the table.
Current status - we have centered the beam on the two irises in SQZT7 but we might have to mechanically offload ZM5 or perhaps ZM4 as well. ZM5 has all four dog clamps attached and baffle installed as well.
We removed the yellow viewport cover (and guillotine) from HAM5, removed the foil and opened the gate valve on HAM7 viewport (going towards HAM5) and then confirmed that the beam is injected into HAM5.
Sheila, is fine tuning the IFO alignment before aligning the two beams (IFO and squeezer) in HAM6 photodiode.
We also did some power measurements in HAM7 chamber, mainly on the OPO and then compared it against SQZT7 table. Sheila will posting the numbers later on.
Power budget: We measured 1.35mW out of the OPO, and 1.2mW on SQZT7. we struggled as usual with the reliablity of the power meter measurements, but it seems like the return beam through SFI1 has higher loss than it should, and there also seems to be power missing between the beam leaving the VIP and the beam arriving on SQZT7. If we believe this measurement we have too much loss, with 12% measured loss in HAM7 where we should have 4-5%.
I did walk the alignment of ZM1/2/3 a little bit, we could try this more to see if we can fix clipping that way. Screenshot of where I left the sliders is attached.
Elenna and I put SR3 back to where it was in O3, aligned SR2 to center on AS_C, and ran the AS centering + offloaded. We then tried to align SRY, but could not get the fringes as high as they should be. We paused on SRY alignment to inject sqz into HAM6.
The sqz beam was on the HAM6 QPDs, we ran the AS WFS to ZM4+5 loops descirbed in 90742. This is close to saturating ZM4 + 5 but is within the range. (We would like to increase the range on these as was done at LLO to make things easier).
We set the OMC PZT offset to 0, decided to scan the psams through strain gauge values of