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Entry  Sat Nov 13 15:53:05 2010, yuta, Update, CDS, diagonalization of MC input matrix MCspectraNov09.pngMCspectraNov13.pngMC1spetra_wrongmatrix.png
    Reply  Sun May 15 03:58:19 2011, rana, Update, CDS, diagonalization of MC input matrix mc1.png
       Reply  Thu May 19 00:23:44 2011, rana, Update, CDS, diagonalization of MC input matrix 
       Reply  Sun Jun 26 16:17:22 2011, rana, Update, CDS, diagonalization of MC input matrix inMatDiag.pdf
          Reply  Mon Aug 8 00:12:58 2011, rana, Update, CDS, diagonalization of MC input matrix 
             Reply  Mon Aug 8 00:58:26 2011, rana, Update, CDS, diagonalization of MC input matrix null.png
                Reply  Wed Aug 10 00:21:10 2011, jamie, Update, CDS, updates to peakFit scripts 
                Reply  Sat Aug 27 15:47:59 2011, rana, Update, CDS, OSEM noise / nullstream and what does it mean for satellites Untitled.png
                   Reply  Wed Nov 30 01:35:49 2011, Jenne, Update, CDS, OSEM noise / nullstream and what does it mean for satellites 
             Reply  Mon Aug 8 19:45:27 2011, jamie, Update, CDS, activateDQ script run; SUS channels being acquired again 
Message ID: 5312     Entry time: Sat Aug 27 15:47:59 2011     In reply to: 5137     Reply to this: 6048
Author: rana 
Type: Update 
Category: CDS 
Subject: OSEM noise / nullstream and what does it mean for satellites 

In the previous elog of mine, I looked at the nullstream (aka butterfly mode) to find out if the intrinsic OSEM noise is limiting the displacement noise of the interferometer or possibly the Wiener FF performance.

The conclusion was that its not above ~0.2 Hz. Due to the fortuitous breaking of the ITMX magnet, we also have a chance to check the 'bright noise': what the noise is with no magnet to occlude the LED beam.

As expected, the noise spectra with no magnets is less than the calculated nullstream. The attached plot shows the comparison of the LL OSEM (all the bright spectra look basically alike) with the damped

optic spectra from 1 month week ago.

From 0.1 - 10 Hz, the motion is cleanly larger than the noise. Below ~0.2 Hz, its possible that the common mode rejection of the short cavity lengths are ruined by this. We should try to see if the low frequency

noise in the PRC/SRC is explainable with our current knowledge of seismicity and the 2-dimensional 2-poiint correllation functions of the ground.

So, the question is, "Should we try to upgrade the satellite boxes to improve the OSEM sensing noise?"

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