Combined report on 4 Dec and 7 Dec 2020. Cont'd from 15551.

Kokeyama, K. Tanaka, Akutsu

Continued inspection in the IFI and IMM chambers using IR laser up to 5W from IMC and that reflected from PRM. There are several things learned. I will summarize them soon, hopefully....

• The PRM angular motion can be fixed with the oplev loop even the chamber is opened and Koach is turned on. (Only once it got crazy.) Anyway, it is so stable that the reflection beam to IFI or to REFL port is stable.
• The beam on STM2 in front of IFI is "now" at the upper edge of he mirror, and so the transmission light is dirty due to the back side structure of the mirror holder.
• "Now", the beam axis in the IFI is shfited toward -Y side.
• As far as we checked all the ghost beams (except for one, which comes from CWP2 to IMM chamber is P) are in S-pols.
• Several expected ghost beams are not found! It is strange. At the same time, several unexpected ghost beams are found as expected. Fig 1 is such a memo on the aluminum foil covering the gate valve between IFI and MCF chamber.
• IFI output side would need a new island, anyhow.
• IMMT2 transmission beams (Fig 2 and 3) (two beams; one is from forward beam, while the other is from backward beam) are not well separated within IFI chamber. If one reflects them by a mirror, the beams go through or partly hit both side of one of the pillars of the IMMT2 suspension... we tried to find a solution to somehow (1) let both of the beams go through the mechanical complicated structure (2) let one of the beam goes though and the other can be separated and dumped. But both strategy did not work well. I would like to dump both beams! Anyway, we confirmed there is a solution that at least the forward transmission of IMMT2 can be tweaked by the steering mirros to go through the IMMT2 susupension structure to outside of the chamber somehow.