[Sheila, Kiwamu]

We spent some time trying to align the simulated beam to the POP QPD sled today in HAM3. Since we got confused by ghost beams for a while, we were not able to finish aligning the beam.

We are aiming to get this whole mission done by the end of tomorrow.

We have set up a fiber-coupled green laser to simulate the red POP path. The output coupler of the fiber is set up on the in-chamber table with a clean base plate underneath it to prevent from contamination. The laser is collimated with a small collimator directly attached on the coupler. The laser beam is then steered by a temporary mirror such that we can perform a fine alignment by touching this mirror. We let the beam go through the scraper baffle and PR2 and all the way to the POP sled. However, in the course of the alignment, we think we got confused by a combination of a ghost beam and extremely dim main beam reflected by a BS in front of QPD_A. This actually had been known to be an issue (see alog 5774 and alog 5924), but we simply forgot this issue and went ahead without paying much attention. We then noticed, at some point, that we had screwed up the alignment by ourself. Sad.

In the tomorrow morning, we will resume the alignment work. Once it is done, we are going to move on to installation of the 90/10 BS and subsequent alignment recovery.