evan.hall@LIGO.ORG - posted 12:03, Friday 04 November 2016 - last comment - 16:59, Friday 04 November 2016(31201)
DARM microseism boost
Matt, Evan
As has been noted before, the DARM residual these days is usually microseism-dominated, and it is getting worse as we move into winter.
We installed a new boost (FM2 in DARM1) to give >40 dB more suppression at the microseism. The performance during yesterday's 25 W lock is shown in an attachment.
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Tagging CAL.
Ryan and I were wondering why is there such a big difference in the residual OMC PD sum between L1 and H1. Both spectra are calibrated in mA so assuming similar optical gains the H1 DARM rms in meters is also 100 times higher than L1 (500 before the boost). This large residual DARM fringe motion may be responsible for the increased/incoherent H1 laser noise coupling.
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We added a boost with resonant gain around 2 Hz. Now the residual is 7×10−3 mA rms below the bounce modes.
The DARM UGF is 70 Hz with 30° of phase.
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