Stefan, Kiwamu, Yuta
Dip at ~13Hz in PRCL OLTF (see alog #10441) was from 40 Hz bandstop filter in PRM_M2_LOCK_L filter bank. When we turned this filter off, PRCL OLTF got much better. We still need a diagonalization of output matrix since we currently use only the BS to lock MICH. To do this, we measured BS and PRM actuation transfer functions (see alog #10450 for more detail) because they have different frequency response. We are now trying to make a conpensation filter to balance BS and PRM actuation from this measurement.
[PRCL and MICH OLTF]
OLTFs after removing the 40Hz bandstop filter are attached. The bandstop filter at 40Hz had -30 deg of phase and it seems like this filter was to blame for PRCL OLTF dip at ~13Hz. This filter was removed.
Demodulation phase of REFLAIR_A was re-tuned to 146.2 deg from 142.7 deg (H1:LSC-REFLAIR_A_RF45_PHASE_R) by minimizing the PRCL to MICH coupling. The LSC guardian is updated accordingly.
MICH to PRCL coupling is unavoidable in the current configuration.
The gain of the MICH to PRCL coupling was fitted with model with coupling at sensing matrix. The parameters I used to fit was 1. optical gain of BS to MICH error signal, 2. BS to PRCL, 3. PR2/PRM to PRCL, and 4. demodulation phase. The parameters I got to fit the measured curve was:
BS PR2+PRM But I think it is unlikely that the demod phase is off by 17 deg. So, we need actual sensing matrix measurement after output matrix diagonalization.
REFL_Q 1.8e2 0
REFL_I -4.9e5 -1.9e6 W/m
and demod phase of -17 deg (when perfect, it will be 0 deg).
