This is a followup of 30335.

On Saturday the IFO lost lock at around 2016/10/08 12:43 UTC (that's 5:43AM Pacific) and PMC also lost lock somewhat later.

1. After relocking, PMC trans drops by about 20% (~20W) while PMC refl doesn't change.
2. 1st loop PDs and refcav trans see the same ~ 20% drop, and refcav refl DC increases.
3. 1st loop QPD sees YAW jump by 2.2um or so, which sounds small but the beam is focused by a lens.
4. No change in HPO power and pointing (discard big dip in DBB_QPD_1QX and 1QS signal, it's just that the uncontrolled DBB PMC flashed due to temperature drift or something).

You can see that the AOM diffraction number changes from 3.7% to 10%, i.e. the AOM transmission decreases by 0.9/0.964~0.93, or 7% drop. I don't know if the AOM calibration is good, but assuming that it is and making correction for this, it still does not make sense.

1. After relocking, PMC trans drops by about 13% (13W) while PMC refl increased by about 7% (36*0.07~2.5W).
2. 1st loop PDs and refcav trans see the same ~ 13% drop, and refcav refl DC increases.

It's not like PMC physically moved (otherwise PMC refl should increase). It seems like something is fishy here. Polarization, alignment, oscillation, what?