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Entry  Thu Apr 12 01:17:56 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam: Possible Clipping BeamProfileData_IPPOS_2.xlsx
    Reply  Thu Apr 12 23:12:16 2012, Suresh, Update, IOO, Beam Profile measurement: IPPOS beam: Possible Clipping 6x
Message ID: 6531     Entry time: Thu Apr 12 23:12:16 2012     In reply to: 6526
Author: Suresh 
Type: Update 
Category: IOO 
Subject: Beam Profile measurement: IPPOS beam: Possible Clipping 


[Suresh, Jenne]

  The input beam is most probably being clipped at the Faraday Isolator.  



We plan to investigate this further to be sure.. 



I tried to determine an optimal WFS2YAW offset to be used so that we may avoid clipping.

Initially, I just measured the beam diameter as a function of offset.  If the beam diameter would become independent of offset if it is not clipped.  However a systematic effect became apparent when I shifted the beam on the detector to a slightly different location.  So I repeated the measurements while recentering the beam to the same location everytime  (centered at -1650+/- 50 for both H and V directions).

I have attached plots of the scans for both cases, with recentering and without.    I have not been able to figure out what is going on since the beam diameter does not become independent of the offset.  While the beam profile becomes more gaussian beyond offsets of about 7 or so, the beam diameter does not seem to follow a clear pattern.  The measurements are repeatable (within one sigma) so the experimental errors are smaller than 1 sigma.

The photographs below show the improvement of Horizontal beam profile with WFS2Yaw offset.  These seem to indicate a good gaussian beam for offsets beyond 7 or so.  At offsets more than 12 the MC unlocks.


Hor_OSet-2.png Hor_OSet0.png Hor_OSet2.png Hor_OSet8.png
 Offset = -2   Offset = 0   Offset = 2   Offset = 8



HorizontalNoRecenter.png  HorizontalRecentered.png
  This seems to indicate that the beam diameter does not vary for WFS2Yaw offset > 8  But if we recenter the beam for each measurement this effect seems to vanish


 Will continue tomorrow.   Jenne wants to do some IFO locking now.


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