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Entry  Wed Nov 18 22:26:33 2015, yutaro, Update, Optical Levers, Calibration of oplevs for ITMY/ETMY calib_etmypit2.pdfcalib_etmyyaw2.pdfcalib_itmypit2.pdfcalib_itmyyaw2.pdfcalib_oplev.zip
    Reply  Wed Nov 18 23:40:01 2015, rana, Update, Optical Levers, Calibration of oplevs for ITMY/ETMY 
       Reply  Thu Nov 19 16:06:54 2015, yutaro, Update, Optical Levers, Calibration of oplevs for ITMY/ETMY 
    Reply  Tue Dec 1 11:26:23 2015, yutaro, Update, Optical Levers, Calibration of oplevs for ITMX/ETMX ep_l.pdfey_l.pdfip_l.pdfiy_l.pdf
       Reply  Thu Dec 3 06:15:38 2015, rana, Update, Optical Levers, Calibration of oplevs for ITMX/ETMX 
          Reply  Thu Dec 3 10:05:07 2015, yutaro, Update, Optical Levers, Calibration of oplevs for ITMX/ETMX 
       Reply  Fri Dec 11 16:16:36 2015, yutaro, Update, Optical Levers, Calibration of oplevs for ITMX/ETMX 
          Reply  Mon Dec 14 23:49:03 2015, ericq, Update, Optical Levers, Calibration of oplevs for ITMX/ETMX 
Message ID: 11790     Entry time: Thu Nov 19 16:06:54 2015     In reply to: 11787
Author: yutaro 
Type: Update 
Category: Optical Levers 
Subject: Calibration of oplevs for ITMY/ETMY 

I'm sorry. I will be careful about that. And I updated the plots in elog 11785.

Quote:

OMG. Please try to use larger fonts and PDF so that we can read the plots.

 

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Based on elog 1403, I calibrated the oplevs for ITMY/ETMY.

I'm not sure that these calibration measurements are reliable. I would feel better if Steve can confirm them using our low accuracy method of moving the QPD by 1 mm and doing trigonometry.

 In this morning, Steve and I looked at the ETMY table and we found that the measurement you suggested might interfere with other optics or detectors because of space constraint. So, before doing this measurement, I roughly estimated the calibration factors for ETMY oplev by using the rough value of the arm length of the optical lever and the beam width of the light just before the QPD.

 

How I got the arm length and the beam width:

I measured the length of the optical path between ETMY and the QPD. Then I measured the beam width with an iris to screen the beam. To get the beam width from the decrease of the power of the beam detected by QPD, I used this formula: P/P_{max}=1-\exp(-2r^2/w^2).

Then I got:   (arm length) = 1.8 +/-0.2 m,    w= 0.56 +/- 0.5 mm.

 

How I estimated the calibration factors from these:

The calibration factors (such as C1:SUS-ETMY_OL_PIT_CALIB; (real angle) / (normalized output of QPDXorY)) can be calculated with: \sqrt{\pi/32}\times w\,/\,(\mathrm{arm\,length}). Then, I got

130\,\pm\,20 \,\mu \mathrm{rad},

though the calibration factors, C1:SUS-ETMY_OL_PIT_CALIB C1:SUS-ETMY_OL_YAW_CALIB, right now are 26.0 and 31.0, respectively. (If I express this in the same way as elog 11785, 5.0 and 4.2 for ETMY_PIT and ETMY_YAW, respectively. they are consistent with yesterday's results.) 

I believe that the calibration factors I estimated today are not different from the true values by a factor of 2 or something, so this estimation indicates that the oplev calibration measurements I did yesterday are reliable, at least for the oplev for ETMY. 

 

 

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