We have temporarily swapped the mirror which combines the HWS path and the ALS path. This is usually a polarizing beam splitter, and we have switched it with a HR 2" optic. This clobbers the HWS path (sorry!)
We wanted to check that some ROC on the beam combining optic is not the cause of the mode mismatch between the green beam and the Y arm. We've just opened gate valves and have the Y arm back now. A look at the Y arm while it is swinging after an initial alignment suggests this did not solve the problem (see attached screenshot). The higher order modes are still ~30% of the fundamental.
Some extra details:
I took the PBS out of the mount, and put it in the box of the new HR mirror and left it on the table. The mirror I installed is E1000652, an ATF 2" HR mirror for 532 at 45 degrees AOI. The new optic is thicker than the PBS, but the mount is such that the front face is at the same position relative to the beam, I removed an extra retaining ring from the mount to compensate for the extra thickness. I tweaked the alignment of the mirror until I saw light on the QPDs, and I checked that the PZTs were not railing.
I switched the optic back, so now everything is back to normal in the ISCTEY layout.
While I was out there I checked the Hartmann path and noted it was clipping on HWS-M5. I then stupidly tried to align the Hartmann path, tweaking HWS-S2, HWS-M5 and HWS-M6 while looking at the HWS live images (comparing to a time with the ring heater on), this is very slow to update. In the end I think I made everything worse so next week I will need TJ's help to fix it up to the beautiful alignment they had before, sorry TJ and Aidan :(
I created a guide to aligning the ETMY HWS to help recover the signal.