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Entry  Thu Oct 7 14:39:50 2010, yuta, Update, PSL, measured PMC's laser power-output relation PMCreflect.png
    Reply  Thu Oct 7 15:05:46 2010, Koji, Update, PSL, measured PMC's laser power-output relation 
       Reply  Thu Oct 7 16:34:06 2010, yuta, Update, PSL, measured PMC's laser power-output relation PMCvis.png
          Reply  Thu Oct 14 12:53:29 2010, yuta, Update, PSL, mesured PMC's visibility vs power relation PMCsetup.pngPDcalib.pngPMCreflect2.png
Message ID: 3717     Entry time: Thu Oct 14 12:53:29 2010     In reply to: 3672
Author: yuta 
Type: Update 
Category: PSL 
Subject: mesured PMC's visibility vs power relation 

 I measured the PMC's visibility vs incident power relation last week to see the thermal effect, but I didn't calibrated the laser power(see elog #3672).
 So, I calibrated it on Oct 12.


 Attachment #1
 The laser grade window PW-1025-UV-1064-45P had power reflectivity of about 0.5% in this setup.

What I did:
1. Calibrated the laser power(Attachment #2).
  To measure the laser power, I put the Ophir power meter at just in front of "PMC REFL PD".

2. For the calculation of the visibility K, I used the following formula;
 K= [1-(R1-R0)/(R2-R0)]*100
where R0, R1 and R2 are the PD outputs in voltage when laser is off, PMC locked and not locked respectively.

3. Plotted the visibility vs the incident power(Attachment #3).

 Attachment #2
  From the linear fit by least squares, the calibration turned out to be 1.12±0.07 mV/uW. The error of this value is calculated from assuming PD output error~1mV and laser power error~3uW for all measured value.
  The largest error was from the position and the angle of the power meter probe.

 Attachment #3
  I used the same data I took last week(see elog #3672), but better plot.
  I put the error bars for just several points. When the laser power is weak, the errors are large because of the cancellation error. When the laser power is high, the errors are estimated to be so small that you can't see it in the plot(~1%).
  At the several points, I couldn't lock the PMC well and  the power of the reflected light depended on the offset voltage of the PZT.
  The horizontal axis has about 6% error because of the calibration error.

 Now the condition is a bit different from this measurement(NPRO temperature changed, optics moved slightly), so the visibility may be changed.

Attachment 1: PMCsetup.png  786 kB  Uploaded Thu Oct 14 23:58:48 2010  | Hide | Hide all
Attachment 2: PDcalib.png  38 kB  Uploaded Fri Oct 15 00:03:45 2010  | Hide | Hide all
Attachment 3: PMCreflect2.png  27 kB  Uploaded Fri Oct 15 00:12:39 2010  | Hide | Hide all
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