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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: 11823     Entry time: Mon Nov 30 10:41:45 2015     In reply to: 11818     Reply to this: 11828
Author: yutaro 
Type: Update 
Category: LSC 
Subject: Does a baffle in front of ETMY have effect on loss map measurement? 

It might have, so I think I need to estimate shift of beam spot more preciely.

 

According to Steve's drawing, radius of the hole of the baffle is 19.8 mm.

Intensity distribution of fundamental mode in x axis direction is this (y is integrated out):

I(x)=\frac{1}{\sqrt{2\pi(w/2)^2}}e^{-\frac{1}{2}\left(\frac{x}{w/2}\right)^2}. 

With the radius of curvature of ETMY of 60 m and the arm length of 37.78 m, the beam width w on ETMY is estimated to be 5.14 mm. From this expression of the intensity, \int^\infty_{x=9.56\mathrm{mm}}\mathrm{d}xI(x)=100\,\mathrm{ppm},\,\int^\infty_{x=10.00\mathrm{mm}}\mathrm{d}xI(x)=50\,\mathrm{ppm}, for example. If round trip loss is considered, these values are doubled.

Although maximum shift of beam spot from the ideal spot on ETMY is estimated to be sqrt(6.0^2+(1.7+1.7)^2)=6.9 mm, this value could have error of several tens of % because I am not sure to what exten the calibration is precise, which means that the maximum shift could be ~10 mm and seperation between the baffle and the beam could be ~10 mm.

Therefore, I need to check how much the beam spot shifts with another way, maybe with captured image of the CCD camera. 

 

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