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Entry  Mon Jul 8 15:31:48 2013, Jenne, Update, ASC, POP QPD calibration prep 
    Reply  Tue Jul 9 11:41:22 2013, Jenne, Update, ASC, POP QPD calibration attempt 
       Reply  Tue Jul 9 16:08:32 2013, Jenne, Update, ASC, POP QPD calibration attempt 
          Reply  Fri Jul 12 21:23:42 2013, Jenne, Update, ASC, POP QPD calibration attempt ChangeVertMicrometer_July2013.pngChangeSideMicrometer_July2013.png
             Reply  Mon Jul 15 17:16:59 2013, Jenne, Update, ASC, POP QPD calibration attempt ChangeSideMicrometer_July2013_calib2.pngChangeSideMicrometer_July2013_calib1.pngChangeVertMicrometer_July2013_calib1.png
                Reply  Tue Jul 16 01:17:21 2013, Jenne, Update, ASC, POP QPD calibration attempt 
                   Reply  Tue Jul 23 01:30:27 2013, Jenne, Update, ASC, POP QPD analysis 9x
                      Reply  Fri Jul 26 13:39:30 2013, Koji, Update, ASC, POP QPD analysis 
Message ID: 8926     Entry time: Fri Jul 26 13:39:30 2013     In reply to: 8897
Author: Koji 
Type: Update 
Category: ASC 
Subject: POP QPD analysis 

It was not actually easy to see from the entry what signal was taken in what condition but from the shape of the spectra
I had the impression that the ASC & OPLEV signals were measured under the presence of the ASC control.
That is (moderately to say) tricky as the ASC control imprints the angular noise
from unkown mirror on the PRM, and then the oplev observes it. The original stability of the oplev is
obscured by the injection from the servo and the fair comparison of the stability is almost impossible.

So the true comparison between the ASC and oplev signals should be done without the control loop.
http://nodus.ligo.caltech.edu:8080/40m/8532

http://nodus.ligo.caltech.edu:8080/40m/8535

We can recover the free running spectrum of the ASC signals by compensating the loop transfer functions
because the ASC signals are the in-loop error signals. The oplev signals should be measured without
the ASC loop engaged.

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