Alignment work summary (Ed, Jason, Travis, Betsy, Koji, Sheila, Keita)

1. IO

We went to HAM3, reinstalled PR2 iris, which was removed by Hugh earlier, to check the beam position on PR2 and there was no beam.

We went to HAM2, the beam was coming to MC1 but the MC1 reflection was not clearing the first MC REFL periscope.

We checked the IOO PZT and sure enough, the offset were at totally bogus numbers. This happened at about the same time when ASC model was restarted (WP 7220 which was circulated at around noon without being noticed by any of the workers involved). We trended the PZT offsets and found that they changed right before we started working. We put the right numbers manually and the beam was on PR2, but it was too high.

When we used PZT to bring the beam back to the center of the PR2, the beam was about a mm or two too high on PRM. We used PZT to center the beam on PRM, and IM4 to center the beam on PR2, but IM4 output railed.

We decided that we need to deliver the beam to the SR chain anyway as Koji is flying back on Friday, so we didn't bother to do anything to IM4 and used PZT to center the beam on PR2. After this (i.e. PZT tweaked for PR2 centering, IM4 railed), the beam position on PR2 is good, PRM is a bit too high (which is not a problem as you'll find in the PR chain alignment).

PZT offsets (before, after) = (-1055.5, -1090.5) for PIT, (-507.4, -737.4) for YAW. Note that there's 90 degrees geometrical rotation from PSL to IO, so IOO PZT PIT is actually YAW in chamber.

Koji found that the iris on PRM was half-closed, this might or might not have been intentionally done yesterday but I told Koji to open it up fully.

2. PR chain to ITMX

PR3 and ITMX centering was already good within a centimeter or so, we didn't have to turn PR2 and PR3 at all. Centering was no worse than yesterday (1cm is limited by our eyeballing the center of a big blob, not by SUS offsets).

This means that the angle of the input beam into PRC is very good, and whatever error coming from the beam position offset on PRM is negligible compared with the uncertainty of the centering accuracy on PR3 and ITMX.

BS centering should be about the same as ITMX.

3. BS to SR chain

We then turned BS to center the beam on SR3. According to Koji's eyeballing, the centering accuracy was like 2cm or so (the beam is fainter than on ITMX and it was moving more than on ITMX).

Then SR3 was moved to center on SR2, then SR2 to center on SRM.

Luckily we didn't have to make a huge change to SR2 YAW slider. PIT didn't change at all.

SR2 slider (before, after) = (1795, 1795) for PIT, (679.5, -210.5) for YAW.

4. Continuing SR chain

We should not attempt to fundamentally fix IO until OFI and SQZ tip tilt alignment are done unless something is totally wrong such that you cannot continue aligning SR chain without fixing IO (e.g. the beam is clipped on one of IO baffles).

The only important thing for OFI and SQZ TT alignment is that the beam is on the right spot on SR2 and SRM. Right now that's the case, so if you're unhappy about the centering on these two mirrors you can use SR3 and SR2.

However, a minor tweak to IM4 and PZT could be done the first thing in the morning. Confirm the beam position on SR2 or SRM before starting to work, whichever is easier, it doesn't have to be centered. IM4 PIT slider is backed off until the OSEMs don't rail any more. PZT YAW (which is PIT in chamber) is adjusted until the beam position is good on PR2. Then PR2 is tweaked until the beam position on SR2 or SRM is recovered.