Summary:

I looked at some DC signals for the buildup of the carrier and sideband fields in various places. The results are shown in Attachments #1 and #2.

Details:

• A previous study may be found here.
• For the carrier field, REFL, POP and TRX/TRY all show the expected behavior. In particular, the REFL/TRX variation is consistent with the study linked in the previous bullet.
• There seems to be some offset between TRX and TRY - I don't yet know if this is real or just some PD gain imbalance issue.
• The 1-sigma variation in TRX/TRY seen here is consistent with the RMS RIN of 0.1 evaluated here.
• For the sideband powers, I guess the phasing of the POP22 and AS110 photodiodes should be adjusted? These are proxies for the buildup of the 11 MHz and 55 MHz sidebands in the vertex region, and so shouldn't depend on the arm offset, and so adjusting the digital demod phases shouldn't affect the LSC triggering for the PRMI locking, I think.
• Based on this data, the recycling gain for the carrier is ~12 +/- 2, so still undercoupled. In fact, at some points, I saw the transmitted power exceed 300, which would be a recycling gain of ~17, which is then nearly the point of critical coupling. REFLDC doesn't hit 0 because of the mode mismatch I guess.