Matt E and I were talking about the broadband noise that is showing up coherently in the OMC DC readout, increasing the noise by 15% or something above shot noise, at frequencies above ~80 Hz. The observation is that this noise increases as the input power is increased (i.e., the watts/rtHz on the OMC DC PDs goes up with higher input power). Amplitude noise on one or more RF sidebands is a plausible source of this noise (not a new idea), and we wanted to suggest specific tests be done to look for RF sideband noise. For example:

• measure the amplitude noise on the 9 MHz and 45 MHz signals coming out of the RF distribution amplifiers in the LVEA that drive the IO EOM (not sure if there are any active devices between these distribution amps and the modulator crystal)
• measure the (AM) noise on the light reflected from the OMC, in full lock (if possible); this light has most of the carrier removed, so any AM on the RF sidebands should be relatively larger than in the OMC transmitted beam (the OMC REFL beam is typically blocked by a beam diverter in low noise, I guess; if the diverter is opened the beam should go to two QDPs in HAM6, if they are aligned)
• measure the RF sideband noise by locking the OMC to one of these sidebands (in DRMI, e.g.); I understand Stefan made an attempt at this already for a 45 MHz sideband -- ?
• of course if the new EOM driver is installed then you could try reducing the modulation index after transitioning to low-noise