(evan jenne nic)
We wanted to investigate the OMC alignment/backscatter problem. Driving the OMC SUS in Yaw has been known to cause backscatter noise due to the modulation of the optical path length when the OMC moves in Yaw.
Our procedure was to lock the vertex optics in a bright michelson configuration (a state has been added to the IFO_ALIGN guardian to make this easy). Then we wanted to drive the OMC in yaw and choose the yaw->longitudinal matrix element such that the center of rotation would be about the input beam, rather than the omc center of mass. This would be determined by minimizing the scatter as measured by either OMC trans, or the MICH error point.
I was surprised that we were not able to induce any significant backscatter fringe wrapping noise in this configuration. We drove the OMC SUS in longitude up to the point that the beam was misaligning enough to noticibly affect the OMC DC trans.
We also drove the ISI table directly by putting a 1Hz 1mm injection into the Y isolation loop error point.
Driving the path length, we both listened and had a live spectrum running. We saw no evidence of scatter in either OMC trans or MICH_IN1.
We will need to think if there is another configuration (available to use without arms) that will be more sensitive to backscatter.
I forgot to mention that we turned on the AS fast shutter and OMC pzt high voltage supplies for HAM6.
This measurement didn't work because I was wrong about the calibration. The isolation loop error points are in nanometers, not micrometers. So we were moving the table 1000 times less than I thought.