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Entry  Thu Apr 29 11:51:27 2021, Anchal, Summary, LSC, Start of measuring IMC WFS noise contribution in ar cavity length noise 
    Reply  Thu Apr 29 15:11:33 2021, gautam, Update, CDS, RFM  RFM_errs.pngScreenshot_2021-04-29_15-12-56.png
       Reply  Thu Apr 29 17:43:16 2021, Koji, Update, CDS, RFM  
       Reply  Thu Apr 29 17:43:48 2021, Anchal, Update, CDS, F2A Filters double check F2AFiltersON.png
          Reply  Fri Apr 30 00:20:30 2021, gautam, Update, CDS, F2A Filters double check 
    Reply  Thu Apr 29 17:51:19 2021, Anchal, Summary, LSC, Start of measuring IMC WFS noise contribution in arm cavity length noise WFS1_PIT_exc_80-100Hz_Arms_ASD.pdf
       Reply  Fri Apr 30 00:18:40 2021, gautam, Summary, LSC, Start of measuring IMC WFS noise contribution in arm cavity length noise 
       Reply  Mon May 3 09:14:01 2021, Anchal, Paco, Update, LSC, IMC WFS noise contribution in arm cavity length noise WFS1_PIT_Noise_Inj_Test_IMC_unlocked.pdfWFS1_PIT_Noise_Inj_Test_ARM_locked.pdf
          Reply  Mon May 3 17:28:58 2021, Anchal, Paco, Rana, Update, LSC, IMC WFS noise contribution in arm cavity length noise excitationoftheMCanglessothatwecanseesomethingdotpng.pngexcitationoftheMCanglessothatwecanseesomethingdotpngbutthistimeitsMC2.png
             Reply  Tue May 4 11:43:09 2021, Anchal, Paco, Update, LSC, IMC WFS noise contribution in arm cavity length noise ArmCavNoiseContributions.pdfIOO-MC1_PIT_NoiseInjTest2.pdfIOO-MC1_PIT_NoiseInjTest_AWGGUI_Config.png
                Reply  Fri May 7 11:54:02 2021, Anchal, Paco, Update, LSC, IMC WFS noise contribution in arm cavity length noise ITMX-XARM_TF.pdfITMY-YARM_TF.pdfArmCavNoiseContributions.pdf
                   Reply  Mon May 10 18:19:12 2021, Anchal, Paco, Update, LSC, IMC WFS noise contribution in arm cavity length noise, Corrections ArmCavNoiseContributions.pdf
                      Reply  Wed May 12 10:53:20 2021, Anchal, Paco, Update, LSC, PSL-IMC PDH Loop and XARM PDH Loop diagram IMC_SingleArm.pdf
Message ID: 16129     Entry time: Mon May 10 18:19:12 2021     In reply to: 16127     Reply to this: 16132
Author: Anchal, Paco 
Type: Update 
Category: LSC 
Subject: IMC WFS noise contribution in arm cavity length noise, Corrections 

A few corrections to last analysis:

  • The first plot was not IMC frequency noise but actually MC_F noise budget.
    • MC_F is frequency noise in the IMC FSS loop just before the error point where IMC length and laser frequency is compared.
    • So, MC_F (in high loop gain frequency region upto 10kHz) is simply the quadrature noise sum of free running laser noise and IMC length noise.
    • Between 1Hz to 100 Hz, normally MC_F is dominated by free running laser noise but when we injected enough angular noise in WFS loops, due to Angle to length coupling, it made IMC length noise large enough in 25-30 Hz band that we started seeing a bump in MC_F.
    • So this bump in MC_F is mostly the noise due to Angle to length coupling and hence can be used to calculate how much Angular noise normally goes into length noise.
  • In the remaining plots, MC_F was plotted with conversion into arm length units but this was wrong. MC_F gets suppressed by IMC FSS open loop gain before reaching to arm cavities and hence is hardly present there.
  • The IMC length noise however is not suppresed until after the error point in the loop. So the length noise (in units of Hz calculated in the first step above) travels through the arm cavity loop.
  • We already measured the transfer function from ITMX length actuation to XARM OUT, so we know how this length noise shows up at XARM OUT.
  • So in the remaining plots, we plot contribution of IMC angular noise in the arm cavities. Note that the factor of 3 business still needed to be done to match the appearance of noise in XARM_OUT and YARM_OUT signal from the IMC angular noise injection.
  • I'll post a clean loop diagram soon to make this loopology clearer.
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