J. Kissel

In order to complete the characterization of the new H1SUSITMX fiber suspension's violin modes while they're now at vacuum, I began driving the PUM stage in Pitch looking for resonances in the L2 OSEMs and the ITMX optical lever in PIT or YAW. I've found nothing. Sadly, the OSEMs are no help, at a sensitivity of ~2e-10 m/rtHz or ~1e-9 rad/rtHz at the fundamental frequencies of the violin modes (~500 Hz), and the optical lever is not that much better at 5e-12 rad/rtHz. My guess is that even the most excited violin modes don't get up past ~1e-15 rad/rtHz.

Sadly, both of these channels are only stored at 256 Hz, so we can't envoke the DetChar / CW groups to run some insanely long FFTs to find them either. All tests done today were with the test point versions of the channels.

I drove awggui with the attached settings (sweeping through the elliptic bandpass' frequency from 500 Hz to 505 Hz with a 1 Hz window at a time, though I started with much broader band passes, 490-515, then 500-505 Hz), and measured the ASD of the above mentioned sensors, looking for coherence between excitation and sensor. Nothing.

The frequencies are motivated by the in-air measurements from LHO aLOG 39135.
Remember, there's a proposal on the table (G1701332) to tailor the frequencies of the violin modes to make them more easily identifiable and to reduce the amount of damping filter commissioning time.
The hope here is to find out what these new at-vac mode frequencies ASAP such that we understand how the evolve from AIR to VAC, with the end goal of being able to predict the mode shift well enough to chose fibers from their in-air measurements.

Advice on how to find these with what limited sensors I have is welcome. 
Otherwise, we'll have to wait until we get some semblance of an IFO up and running -- hopefully a DRMI will be sensitive enough.