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Entry  Wed Aug 9 12:35:47 2017, gautam, Update, ALS, Fiber ALS IMG_3942.JPG
    Reply  Mon Aug 14 16:24:09 2017, gautam, Update, ALS, Fiber ALS IMG_7471.JPGIMG_7472.JPGIMG_7473.JPGIMG_7474.JPG
       Reply  Wed Aug 16 20:24:23 2017, gautam, Update, ALS, Fiber ALS IMG_7476.JPGIMG_7477.JPGIMG_7478.JPGIMG_7479.JPG
          Reply  Wed Aug 23 17:22:36 2017, gautam, Update, ALS, Fiber ALS - reinstalled 
             Reply  Fri Aug 25 15:54:14 2017, gautam, Update, ALS, Fiber ALS noise measurement IMG_7497.JPGFOL_schematic.pdf20170825_IR_ALS.pdf
                Reply  Fri Aug 25 17:11:07 2017, rana, Update, ALS, Fiber ALS noise measurement 
                   Reply  Tue Sep 26 19:10:13 2017, gautam, Update, ALS, Fiber ALS setup neatened IMG_7605.JPG
                Reply  Sun Aug 27 11:57:31 2017, rana, Update, ALS, Fiber ALS noise measurement 
                   Reply  Tue Aug 29 02:08:39 2017, gautam, Update, ALS, Fiber ALS noise measurement 
                      Reply  Fri Sep 1 19:15:40 2017, gautam, Update, ALS, Fiber ALS noise measurement IR_ALS_noise.pdf
Message ID: 13266     Entry time: Tue Aug 29 02:08:39 2017     In reply to: 13257     Reply to this: 13288
Author: gautam 
Type: Update 
Category: ALS 
Subject: Fiber ALS noise measurement 

I was having a chat with EricQ about this today, just noting some points from our discussion down here so that I remember to look into this tomorrow.

  • I believe that currently, the channels C1:ALS-BEATX_FINE_PHASE_OUT_HZ_DQ and the Y arm analog read out the frequency of the green beat, in Hz.
  • In the comparison I plotted, I WRONGLY divided the spectrum of the IR beat by 2, instead of multiplying in by 2, which is what should actually be done for an apples-to-apples comparison.
  • The deeper question is, what should this channel actually readout?
  • Looking at my codes from past arm scans etc, I see that I am dividing the downloaded data by 2 in order to convert the X-axis of these scans to "IR Hz". But this should really be all we care about.
  • So I think I will have to re-do the cts-to-Hz calibration in the ALS models. It should be possible to do ~10FSR scans with the IR beat, and then we can use the sideband resonances (presumably the sideband frequencies are known with better precision than the arm length, and hence the FSR) to calibrate the phase tracker.
  • I don't think this changes the fact that the Fiber ALS situation has been improved - but I will have to repeat the measurement to be sure. The improvement may not be as stellar as I tried to sell in my previous elog sad.

    Other thoughts: 

  • Can we make use of the Jetstor raid array for some kind of consolidated 40m CDS backup system? Once we've gotten everything of interest out of it...

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