We spent some time tuning CM slow servo such that fast path would be stable in the AO gain range -32db -> 29dB (UGF=20kHz) when all boosts are turned off and common gain is 25dB. Current filters that we use for locking are not good enough - AO can not be engaged due to oscillations around 1kHz. This is clearly seen from slow path closed loop transfer function. I will attach servo shapes tomorrow.
Attached plot "EOM" shows EOM rms voltage while changing AO gain from -10dB to 4dB. For UGF of 20kHz we need AO gain of 29dB.
It seems we can start using CM servo for CARM offset but the sensor should be at least factor of 30 better than POY. Add another factor of 10 if we would like to use BOOST 2 and BOOST 3.