Jenne, Rana
In order to symmetrize the hard/soft drives, we want the ITM and ETM actuation functions to be identical (i.e. the PUM pit to TM pit TF). Previously Evan and Rana adjusted the TOP stage damping to make all the TMs the same. We also balanced the common / differential drives using the AS port WFS.
Today we realized that this was not as good as we thought since the PIT optical lever servos were on for the ITMs, but no other OL servos were on. So the PIT DoF was an admixture of hard/soft all of this time. So we measured the OLG for all of the TMs and turned on the loops for the ETMs, so now the PIT OLDAMPs are on for all the TMs. The same filters are ON for all 4 loops, and we adjusted the gains to make the OLG sweeps look the same (to within ~10-20%):
G_ITMX = -300
G_ITMY = -300
G_ETMX = -440
G_ETMY = -300
Attached is a measurement of the pitch oplev loops for each test mass, after we've adjusted the gains so that they match. It's unclear why ETMY's phase is a little different.
It worked s expected! Adding the OL damping on the ETMS symmetrized the drives and made the hard loop TFs more smooth - less notches. Only Pitch though; yaw TF still looks weird.