J. Kissel, D. Hoak, A. Pele, G. Merano
Spearheaded by my blind hopes of obtaining measurements of all 6 resonant modes of the suspended bench of the H1 SUS OFI -- an otherwise abandoned suspension, to confirm / refine the recently developed OFIS model -- Arnaud, Dan and Gerardo helped me construct various configurations of a (clean) laser pointer (literally a laser pointer) and an old QPD as a crude shadow sensor / optical lever. The normalized amplitude spectral densities are attached. I was able to confirm the two of the three modes already measured (Long and Vert -- see LHO aLOG 12588), but the only new mode I could get (without hours more pain, and MUCH better equipment / hardware) was the Yaw mode (which did at least roughly agree with the 1.1 [Hz] yaw mode from the model as it currently stands). Unfortunately, as we've learned from every other suspension, the Pitch and Roll modes are those which constrain the model the best. I did not reconfirm the mode's Qs.
Ah well. Details and pictures below.
The lack of mode frequency and Q should not hold up close-out of this chamber, but as a last ditch effort, we should at least try to get this information from 3IFO's OFI.
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Details:
Measured Resonances:
L* - 0.6306 or 0.6263 [Hz] (15 [mHz] or 7 [mHz] bin width, Configuration 2 & 1, respectively)
V - ~1.05 [Hz] (7.5 [mHz] b.w., Config. 3, noisy and low-Q)
Y - 1.058 or 1.084 [Hz] (15 [mHz] b.w., and Config 2 or 3, respectively)
* the L and T mode are virtually degenerate and given the spew of light and iffy spot on the QPD, this could be either.
See attached images for configuration descriptions. I was pretty limited given the clean hardware and table space I had as to how and where I could reflect or shadow light. Very few of the surfaces at the beam / QPD heights I had were reflective, and there were only a few bolt-holts that allowed for a good beam-to-QPD path. Not to mention the quality of the beam coming out of the laser pointer was garbage, the QPD only read out one DOF (the X channel was reported twice out of the preamp #facepalm), and ambient motion was just barely enough to get the first three modes above the noise floor of the QPD at its maximum gain setting (used in config 2 and 3). If this ever needs measuring again (say if the 25 [Hz] modes appear in DARM from some second-order dirt effect) we should really think about the measurement technique.
Thanks again to Gerardo, Dan, and Arnaud for their help!
