Following Keita's entry from last week, we are now running with the OMC in a lower-gain state to reduce the length actuation.  First plot attached is a OLTF measurement of the OMC LSC loop while in low noise; the current Guardian settings bring us to the blue curve, with a UGF of about 15Hz.  For the blue and green curves the OMC-LSC_SERVO_GAIN = 10, the red curve had a gain of 60 and a larger boost.  We thought about turning off the boost entirely, which would give us the green curve -- for now we've left it on.

This gave us a good improvement in the upconverted noise around the OMC length dither line, see second figure which is the noise from late Friday night.  (The areas of improvement compared to the blue reference, from Thursday morning, are annotated.)  There is still some upconverted noise, see third figure, and we could reduce the OMC length gain even further. 

To do: estimate the OMC length noise --> DARM coupling using Koji's noise measurements of the intrinsic length noise in the OMC to see how much length noise suppression we need.