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tomotada.akutsu - 23:47 Tuesday 09 February 2021 (15970) Print this report
Searching for ghost beams of IMC

K. Tanaka, Yano, Nakano, Akutsu

Continued from 15942.

We searched for ghost beams in the MCF chamber and comfimed there were no "strange" ghost beams so far. Today's situation is summarized in Fig 1 and 2.


Today we made the incident light be S-pol in the PSL room and did the check around MCi. Then the polarization was changed to P also in the PSL room to check around MCo (the same reason as in 15830). We finally use about 1 W at the IMC REFL (just estimated from a power meter (by Ophir) at the side of the first periscope on the IMC_REFL table.)

Around MCi

  • Ghost beam (GB) "R" from a high quality viewport between the PSL room and the MCF chamber was not seen when we used the S-pol input beam.
  • GB "S" and "T" would be unrealistic because they are created at the high quality viewport by a reverse beam from MCi to the PSL room.
  • GB "J" was observed, and caught with a beam dump more close to the MCi than what shown in Fig. 1. Maybe we put it here at iKAGRA era... klog may exsit.
  • GB "N" was observed (Fig. 3), and caught with ta beam dump shown in Fig. 1; actually it is slightly out of the dump so it should be relocated slightly later.
  • GB "M" would be too faint to see.
  • GB "K" and "L" were observed (Fig. 4), and are caught by a beam dump more close to the high quality viewport window for IMC_REFL than what shown in Fig. 1. Actually these ghost beams were split in slightly vertical, and the beam dump slightly missed to catch all, so needs to be relocated later.

Around MCo

  • GB "b", "c", and "V" would be unrealistic, as they are created by the reverse beam.
  • I assumed Kenta and Nakano observed GB "f" with P-pol the other day, but today I could not obverve it with S-pol (Oh I forgot to check it by my eye balls...). I'm afraid we can not ignore this ghost beam; maybe this ghost beam would be the one at the left side of the Fig. 2 of 14200. We need to determine it later carefully.
  • GB "a" was observed (Fig. 5) with P-pol but not with S-pol. In the same manner as GB "f", We need to determine it later carefully.


  • Do not forget that the actual situation the light beam is resonant in IMC.
  • Any other notes might be added in wiki.
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