Corey, Daniel, Evan

For the past 24 hours the green transmission through the X arm has been uncharacteristically unstable, sometimes dipping to less than 60% of its maximum value on timescales of a few seconds.

Looking at the quad oplev signals, it seems that this dipping (perhaps unsurprisingly) is mostly associated with EX pitch. It could be because of wind (there were gusts above 40 mph yesterday), or it could be because of the microseism (the 0.1­–0.3 Hz STS bands peaked yesterday around 0.4 µm/s, which is the highest they've been in the past 90 days, excepting earthquakes), or it could be because of something else entirely.

Turning down the EX green WFS pitch gain (H1:ALS-X_WFS_DOF_1_P_GAIN) by a factor of 5 seems to lessen the fluctuations in the transmitted green signal, making it stay within 75% of its maximum. It is a small effect, but it seemed to make an improvement for the transmitted IR light in the CHECK_IR step.

After this change we were able to make it past SWITCH_TO_QPDS and all the way to nominal low noise. It could just be a coincidence, though.