The night before last, OMC injections suggested that our scattering problem did not involve a back-reflection from the OMC. While looking at the data, I noticed that the injections seemed to excite a 0.05 Hz oscillation (servo?) that did produce scattering up to 100 Hz. The time series in the figure show the 85-90 Hz band of DARM against vertical and horizontal OMC OSEMs. The longitudinal injection is between about 1400 and 1800s and is visible on the T3 OSEM but not on the vertical OSEM. The 0.05 Hz oscillation starts near the end of the injection.  The level of motion that produced shelves to 100 Hz was not that much greater than normal motion. This suggests that we should try exciting the OMC in other degrees of freedom, in case the scattering is in another direction besides the main beam direction. I think vertical injections would be the place to start because vertical seems to correlate the best; perhaps light is scattering back from the shiny table top just below the upside down OMC. 

Robert, Koji, Sheila