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Entry  Wed Nov 25 16:40:32 2015, yutaro, Update, LSC, round trip loss of Y arm 
    Reply  Wed Nov 25 23:34:52 2015, yutaro, Update, LSC, round trip loss of Y arm 14.png
       Reply  Fri Nov 27 03:38:23 2015, yutaro, Summary, LSC, round trip loss of Y arm image1.png
          Reply  Fri Nov 27 22:20:24 2015, yutaro, Update, LSC, round trip loss of Y arm log.txt.zip17.png
          Reply  Sat Nov 28 11:46:40 2015, yutaro, Update, LSC, possible error source of loss map measurement 
          Reply  Mon Nov 30 10:41:45 2015, yutaro, Update, LSC, Does a baffle in front of ETMY have effect on loss map measurement? 
             Reply  Mon Nov 30 17:17:30 2015, yutaro, Update, LSC, Does a baffle in front of ETMY have effect on loss map measurement? element2-2.pngelement0-0.pngelement4-4.png
          Reply  Mon Dec 7 11:11:25 2015, yutaro, Summary, LSC, round trip loss of X arm image1-2.JPGsymmetry.png
Message ID: 11820     Entry time: Sat Nov 28 11:46:40 2015     In reply to: 11818
Author: yutaro 
Type: Update 
Category: LSC 
Subject: possible error source of loss map measurement 

I found that TRY level degraded and the beam shape seen with CCD camera at AS port was splitted when the beam spot on ETMY was not close to the center. This was because dither started not working well. I suspect so because in such a case TRY level went up when I did iteration with TT1 and TT2 after freezing dither. Splitted beam shape indicates that incident light did not match well with the cavity mode.

TRY level for each point was this:

TRYDC
[[ 0.6573      0.8301      0.8983      0.8684      0.6773    ]
 [ 0.7555      0.8904      0.9394      0.8521      0.6779    ]
 [ 0.6844      0.8438      0.9318      0.8834      0.6593    ]
 [ 0.7429      0.8688      0.9254      0.8427      0.6474    ]
 [ 0.7034      0.8447      0.8834      0.8147      0.6966    ]]

 In the worst case, TRY level was 70 % of the maximum level. Assuming that this degrade was totally due to the mode mismatch, this corresponds to ~50 urad difference between the angle of incident light and resonant lighe in the arm (see elog 11819).

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