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Entry  Tue Apr 10 00:50:56 2012, frank, tara, DailyProgress, optic, bad PBS 
    Reply  Wed Apr 11 02:44:29 2012, frank, tara, DailyProgress, optic, bad PBS beat_2012_04_10.png
       Reply  Wed Apr 11 20:30:50 2012, frank, tara, DailyProgress, NoiseBudget, Electronic noise verification beat_2012_04_11.png
          Reply  Thu Apr 12 22:22:12 2012, frank, tara, DailyProgress, NoiseBudget, Electronic noise + shot noise verification 
Message ID: 905     Entry time: Tue Apr 10 00:50:56 2012     Reply to this: 906
Author: frank, tara 
Type: DailyProgress 
Category: optic 
Subject: bad PBS 

We noticed wide angle scattered light behind the PBS in front of RCAV. The scattering source is probably the curved mirror behind RCAV AOM. We borrowed the similar mirror from 40m and will try to compare them.

      The wide angle scattered light behind the PBS in front of RCAV might contribute to the noise in beat signal. The picture shows the scattered light with area larger than the half inch PBS cube. This picture was taken when the beam's polarization was changed to P-polarization so that most of the light was reflected from the PBS. With small transmitted light through the PBS, the scattered light can be seen clearly behind the PBS, see here

     After the inspection, it is very likely that the curve mirror behind RCAV AOM is the source. So we borrowed another R=0.3 mirror from 40m to see if it will be better or not, this will be done soon.

     Note: during the inpsection, we also identified another bad PBS,pic. This is the one in front of RCAV AOM. Its center surface looks dirty, so we replaced it with a better one.

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