[Koji / Kiwamu]

 We have realigned the interferometer except the incident beam.

 The REFL beam is not coming out from the chamber and is likely hitting the holder of a mirror in the OMC chamber.

So we need to open the chamber again before trying to lock the recycled interferometers at some point.

--- What we did

•  Ran the MC decenter script to check the spot positions.
  • MC3 YAW gave a - 5mm offset with an error of about the same level.
  • We didn't believe in this dither measurement.
•  Checked the IP-POS and IP-ANG trends.
  • The trends looked stable over 10 days (with a 24 hours drift).
  • So we decided not to touch the MC suspensions.
• Tried aligning PRM
• Found that the beam on the REFL path was a fake beam
  • The position of this beam was not sensitive to the alignment of PRM or ITMs.
  • So certainly this is not the REFL beam.
  • The power of this unknown beam is about 7.8 mW
• Let the PRM reflection beam go through the Faraday
  • This was done by looking at the hole of the Faraday though a view port of the IOO chamber with an IR viewer.
• Aligned the rest of the interferometer (not including ETMs)
  • We used the aligned PRM as the alignment reference
  • Aligned ITMY such that the ITMY reflection overlaps with the PRM beam at the AS port.
  • Aligned the BS and SRM such that their associated beam overlap at the AS port
  • Aligned ITMX in the same way.
  • Note that the beam axis, defined by the BS, ITMX  and SRM, was not determined by this process. So we need to align it using the y-arm as a reference at some point.
  • After the alignment, the beam at the AS port still doesn't look clipped. Which is good.

---- things to be fixed

   - Align the steering mirrors in the faraday rejected beam path (requires vent)

   - SRM oplev (this is out of the QPD range)

   - ITMX oplev (out of the range too)