In response to Keita's alog (here) I changed the whitening gain and number of active filters on the ITMx, ITMy, and ETMx optical levers. They are now set as outlined in the 2nd table in Keita's alog. I also enabled the corresponding de-whitening filters in the oplev filter medm screens (ITMy and ETMx only, as these were the only ones that had additional whitening filters enabled) and accepted the changes in SDF.
I took spectra of each segement of the QPD for each TM oplev, both before and after the de-whitening filters (channels labeled IN1 are before de-whitening, channels labeled OUT are after de-whitening) as well as spectra of the pitch and yaw signals of each oplev.. To my knowledge, ETMx and ETMy look as they are supposed to. On the other had, the ITMx and ITMy QPD spectra do not look right to me. When I took the spectra there were ongoing investigations into ITMx ISI coil driver issues and ITM charge measurements (ie, the optics were moving); also, the oplev lasers for both ITMx and ITMy oplevs are unstabilized lasers, sitting on the LVEA floor. All of these could be causing issues with the measurements; they should be re-taken once things have quieted down and see if there are differences. If there are no differences, I fear we may have made things worse for the ITMs. There also appears to be a comb in all of the ITMy spectra. I think this is caused by the laser glitching; as soon as I have a stabilized laser ready for install this laser is getting replaced.
This completes WP #6020.
ITMX looks good to me. All quadrants look similar to each other and the PIT plot looks better than before (e.g. https://alog.ligo-wa.caltech.edu/aLOG/uploads/28615_20160725101947_Screenshotfrom2016-07-2510%3A01%3A12.png).
ITMY looks OK-ish to me except at high kHz for segment 1 and 3, which need to be investigated further. But the thing is that ITMY used to be without any whitening gain and filter that there was no way this kind of oddness could have been revealed before. See the attached plot of the current ITMY oplev signals with the pink line showing the old noise floor, and compare with the above mentioned old plot.
