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Entry  Tue Jan 10 00:09:33 2012, kiwamu, Update, LSC, spike hunting in REFL33 
    Reply  Tue Jan 17 01:02:07 2012, kiwamu, Update, LSC, glitch hunting in REFL RFPDs : strange PRMsingle_bounce.png
       Reply  Tue Jan 17 02:27:49 2012, kiwamu, Update, LSC, fringe tests : all the suspensions are innocent 
       Reply  Tue Jan 17 13:47:40 2012, kiwamu, Update, LSC, dirty steering mirror in the REFL path 
          Reply  Wed Jan 18 12:36:26 2012, kiwamu, Update, LSC, wiped a steering mirror on the REFL path DSC_3861_small.jpgDSC_3863_small.jpg
       Reply  Tue Jan 17 19:07:47 2012, rana, Update, LSC, glitch hunting in REFL RFPDs : strange 
       Reply  Wed Jan 18 14:28:36 2012, kiwamu, Update, LSC, estimation of optical length between PRM and scattering object calibration.pngscattering.png
          Reply  Wed Jan 18 16:31:10 2012, kiwamu, Update, LSC, estimation of optical length between PRM and scattering object ND1atten.png
Message ID: 6212     Entry time: Wed Jan 18 16:31:10 2012     In reply to: 6211
Author: kiwamu 
Type: Update 
Category: LSC 
Subject: estimation of optical length between PRM and scattering object 

I searched for a scattering body in the REFL path.

According to the result the REFL path on the AS table is innocent.

 

The idea of the search method is given as follows:

  •   Put a 1/10 ND attenuator at the origin of the REFL path on the AS table.
  •   Of course this reduces the signal level by the same factor of 10 in the REFL11_I demod signal.
  •   If the scattering body is in the REFL path the up conversion noise will be smaller by a factor of 100 because the scattered light go across the attenuator twice.

 

 The attached plot below is the spectra of REFL11 with the 1/10 attenuator at the origin of the REFL path when the beam is single-bounced from PRM.
In the measurement PRM_POS was driven at 10 Hz with an amplitude of 1700 all the time. This is exactly the same situation as that explained in the previous elog entry (#6211).
You can see that the up conversion noise level also decreased by the same factor of 10, which suggests there are no scattering object in the REFL path.
Note that the data with the attenuator in place is intentionally scaled by multiplying a factor of 10 for comparison.
ND1atten.png
 

Quote from #6211

Assuming that PRM is interfering with some other optics, I have estimated the optical distance between PRM and an object that interferes with PRM.

The optical distance is estimated to be 9.5 +/- 0.5 m.

If we believe this number the object is most likely outside of the vacuum chambers.

 

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