Ushiba, Miyamoto, Izumi,

Tonight, we tried to find the interferometer beam at EYC, but didn't have good luck.

Activities (in chronological order)

• The pieces of aluminum foil at the IMMT chambers were removed to let the beam enter the rest of the chambers.
• We aligned IMMTs and PRs back to the zero positions of their optical levers.
• The interferometer beam was found at EXA by running the usual Lissajous scan on the PR3 angle (e.g., 3584).
  • PR3 needed to be at (P, Y) = (-35 urad, -85 urad) as read from the optical lever.
  • I am guessing that the reason why the yaw needed to be such big is due to the change in the cavity axis of IMC. The IMMT1 trans showed a relatively large number of 0.5 in yaw.
• We performed the Lissajous scan of the BS angle multiple times with different amplitude and frequency settings. While doing so, we kept looking at the baffle PD signals (3967).
  • We couldn't find the beam.
  • The biggest scan range is about (P, Y) = (+/- 200 urard, +/- 200 uard).
• In parallel to this, Ushiba-kun and Miayamoto-kun found the strange behavior of the cryogenic payload in which the oplev signals became suspiciously quiet. In this situation, rotating the BF by the stepping motor didn't seem to make an appreciable movement of the payload as seen by the optical lever.

Things to check

• The baffle PD gains and expected volitage outputs.
• The spot position on the BS and the beam clerance at the BS-IYC gate valve.
• Another round of the visual inspection on the cryogenic payload to make sure things are not rubbing or touching.
• If possible, another look at the beam clearnce at the IYA gate valve.