The figure shows spectra from the 4 angular IMC WFS DC channels with labeled peaks. Eight of the peaks between 80 and 1000 Hz are from optics or structures on the PSL table, two were from IOT2 and four haven’t been identified. The unidentified peaks were not excited by our PSL injections, even the global ones. It is possible that they are associated with structures that weren’t excited on IOT2 or in HAM2, or they may be associated with structures on the PSL table that we weren’t able to excite.
The identified sources are table resonances, periscope resonances and optic mount resonances. All optics that produced peaks in the spectrum were downstream of the PMC and were mirrors rather than through-optics like lenses, as would be expected.
The figure also shows the location of the sources in the PSL, as well as samples of the bowing and tapping data used to make the identifications.
Robert, Craig
This version of the jitter spectrum includes photos of the optics. It should be easy to lower the Q of some of the higher-Q optics like M3.
This is a very interesting and impactful glimpse into the current state of PSL table jitter coupling. Wish I had noted the study on first release.
I'm sure many would be interested in seeing an equivalent study of LLO, in everyone's spare time 
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This study is relevant to IIET Ticket 4639 with title: "ECR: Modify attachment of optics mount to mounting plate on PSL periscope, previously Bug 1140". This IIET Ticket corresponds to the upper periscope mirror mount, with designator IO_MB_M6.
This study is relevant to IIET Ticket 5132 with title: "Move IO input beam PZT-mount from periscope to PSL/IO table surface". This IIET Ticket corresponds to the steering mirror upstream of the periscope which has a PZT actuator, with designator IO_MB_M4.
This effort was subsequently re-examined by Robert in
https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=44460