camilla.compton@LIGO.ORG - posted 17:05, Friday 05 June 2026 (90505)
HAM7 Vent, Day 4. Friday 5th June
Begum, Ryosuke, Camilla, Madi
Summary: Were able to retroflect the beam off FC1 (when placed at O4 sliders) with ZM2 and ZM3 but the beam height is incorrect, as expected, VOPO optics will need to be moved to fix this.
Checking current Beam location:
Started the day by checking the beam path with our alignments as left yesterday 90467. With FC1 P slider at O4 nominal 225 (WIT at 165), we have: beam ~4mm low on ZM3 iris, 1” off FC REFL iris (beam up and right), not retroreflected ~3mm off being retro-reflected at ZM1 and 0.5mW on IR PD. I'm was little surprised that we have any light in the IR PD but this makes some sense as the beam is far from retroflected so it's going into the FC at a strange angle. With FC1 WIT moved to 185, IR REFL got better, to 0.8mW but this doesn't mean anything so leave at original plan of FC1P slider at 225.
Setting FC Retrorefection
We then got the IR beam reflected off FC by adjusting ZM2 and ZM3. I first did this by moving ZM3 for co-alignment at the ZM1 iris, then moving ZM2 to co-align at A:M3. Then noticed YAW was a little off at A:P1 so adjusted ZM2. Begum later came out with a card with a hole in it and slightly adjusted these co-alignments by mis-aligning in pit to check yaw and vice versa. Ending screenshot attached.
It’s now not making it through B:L1, high and slightly left (towards -X). It is low and slightly left (-X) on ZM3 iris.
Green beam not making it to FC REFL iris LPM.
Beam height Measurements
The nominal beam height between ZM3 and FC1 is 6.288" however out beam is low, ~6". We measured it to be the same both close to ZM3 and as far towards FC1 as we could reach so it is at least retro-reflecting off FC1 horizontal, this is good. At ZM2 it was 6" and at ZM1 it was 5.5", we expect it to be 5.532" high here (60068) and rise up between ZM2 and ZM3 but it appeared to be rising between A:M3 and ZM2. ZM1 sliders have always been 0,0. Photos of height measurements attached.
We expect that we need to change A:M3 and other VOPO optics to get the beam both retro-reflecting off this FC1 angle with the correct beam height.
End of day
We then tried to take more Phasics camera measurements but struggled with the camera connection.
We also went back to SQZT7 IR PD alignment, ready to check before the B:L2 aperture move, but the alignment wasn't the same. This was confusing, I went back to the alignment we set the ZM1 and ZM3 iris and the alignment looked fine there and on SQZT7. To be continued...
Images attached to this report
