Picomotor mistery solved: It was an in-chamber cable. Unlike the ones Corey looked at in the lab today, what we have in chamber is "A"=J5, "D"=J2. See Alexa's alog.

In-chamber alignment done: We adjusted the IR QPD sled. Since we already rotated the 50-50 BS 180 degrees yesterday, there was no way the QPD sled could be left untouched, but anyway when we started it was not that bad, and only a small touch up was necessary.

One thing we did NOT understand is why it was easy to do this this time. If you remember the story from EY installation, the reflectivity of 50-50 IR splitter is almost zero for green S (correct) polarization, and it was almost impossible to find the right beam without using a bad polarization. This time, however, it was easy to see the beam with the beam leaving the table as is, and rotating the polarization 90 degrees made it worse.

Maybe the existence of the first contact on the HR side of ETMX is doing something funny for the polarization, though the transmissivity of HR for green is between 3% and 15% according to witness sample measurement by LIGO and 27% according to LMA (https://dcc.ligo.org/C1103232) so it's not that likely that the FC is doing something significant.

Becoming suspicious if we're using correct optics, we checked the DCC number of 1" IR 50-50 splitter and 1" high reflector, but they were both correct.

Anyway, the important thing is that the green leakage light into IR QPD sled is centered on QPDs when the ETM is retro-reflecting the beam, and we (Kiwamu and I) are quite confident that the beam we're looking at is the correct one.

BOSEMs were checked, they 're not touching, and the centering is not terrible either (though certainly it's not perfect). We set the depth of BOSEMs so the output becomes 15000-ish.

Some tools that are not ours are left in chamber.

What's next:

1. Jeff K will take another TF. If it's good, we'll NOT touch BOSEMS.
2. After that, we can give the chamber back to IAS for ACB alignment, and to the SUS.
3. Before closing out, we MIGHT want to push the dust particulates off of the telescope optics using nitrogen gun and wipes (they're dirty and you can see it from the pictures), before pulling the first contact from ETMX.