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Entry  Fri Nov 1 17:54:47 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Ouput under inspection NFSS_RFPD_Output_Oscilloscope.pdfSFSS_RFPD_Output_Oscilloscope.pdfNFSS_RFPD_RF_OUT_COUPLED.pdfSFSS_RFPD_RF_OUT_COUPLED.pdf
    Reply  Tue Nov 5 18:37:59 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS Testpoint Spectrum Data FSS_TP_Spectrum.pdf
       Reply  Sat Nov 9 19:28:36 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Loop nonlinearity Test NFSS_NonLinearity_Test.pngSFSS_NonLinearity_Test.pngsignal-attachment-2019-11-09-195635.jpeg
          Reply  Mon Nov 11 20:42:49 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Two Tone Test NFSS_RFPD_SN009_TF_11-11-2019_183131.pdfSFSS_RFPD_SN010_TF_11-11-2019_203310.pdfFSStwoToneTest.pdf
             Reply  Tue Nov 12 18:36:59 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Two Tone Third Order Intermodulation Test FSStwoToneThirdOrderIM.pdf
                Reply  Thu Nov 14 12:19:32 2019, rana, DailyProgress, FSS, FSS Diagnostics - Two Tone Third Order Intermodulation Test 
                   Reply  Tue Nov 19 18:51:02 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Second-order Distortion Calculation FSSDistortionCalc.pdfFSSDistortion.zip
                      Reply  Mon Dec 9 19:54:44 2019, anchal, DailyProgress, FSS, FSS Diagnostics - How much distortion affects the functioning of PDH? 
       Reply  Wed Nov 27 13:59:24 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS TP1 TimeSeries NFSS_TP1_Oscilloscope.pdf
          Reply  Wed Nov 27 15:17:51 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Quick HF OLTF of NFSS NFSS_OLTF_HF.pdf
             Reply  Wed Nov 27 16:31:20 2019, rana, DailyProgress, FSS, FSS Diagnostics - Quick HF OLTF of NFSS 
                Reply  Wed Dec 4 18:11:09 2019, anchal, DailyProgress, FSS, Free running laser frequency noise spectrum PMCErrorSignals.pdf
                   Reply  Thu Dec 5 18:25:11 2019, rana, DailyProgress, FSS, Free running laser frequency noise spectrum 
                   Reply  Tue Dec 17 18:29:58 2019, anchal, DailyProgress, FSS, Need for ISS? 
                      Reply  Wed Dec 18 18:40:32 2019, anchal, DailyProgress, FSS, Maybe the NPRO Laser isn't bad after all NorthLaserRINAnalysis.pdf
                         Reply  Wed Dec 18 22:03:17 2019, rana, DailyProgress, FSS, Maybe the NPRO Laser isn't bad after all 
                            Reply  Fri Dec 20 15:00:30 2019, anchal, DailyProgress, FSS, PZT, EOM to RIN TF Measurement NorthLaserPZTEOMtoRINTF.pdf
                               Reply  Fri Dec 20 18:08:44 2019, anchal, DailyProgress, FSS, PZT, EOM to RIN TF Measurement Through FSS NorthLaserPZTEOMtoRINTFThruFSS.pdf
                                  Reply  Tue Jan 7 17:59:20 2020, anchal, DailyProgress, FSS, NPMC TF NPMC_TF.pdf
       Reply  Thu Dec 12 19:15:55 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Beatnote Spectrum wrt Laser Power and Modulation Index BeatnoteSpectrumwrtPowerandModindex.pdf
       Reply  Tue Dec 17 16:55:07 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS North U7 Boost Stage Input-Output TimeSeries NFSS_UT_TS_Analysis.pdf
    Reply  Tue Nov 12 11:39:48 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Ouput under inspection 
    Reply  Fri Dec 13 16:24:02 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD Circuit Latest Available Photos SN009.jpgSN010.jpgSN009.jpgSN010.jpg
    Reply  Fri Dec 13 17:44:05 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Coupled Output Offset 
       Reply  Mon Jan 13 19:04:38 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN009 (North RFPD) Notch Improvement Attempt SN009.jpgSN009_D980454-00-C.pdfSN009_Notch_Improvement_Attempt.pdf
          Reply  Tue Jan 14 18:19:33 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN009 (North RFPD) Notch Improved! SN009.jpgSN009_D980454-00-C.pdfSN009_Notch_Improvement_Attempt.pdf
             Reply  Thu Jan 16 11:17:15 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN010 (South RFPD) Notch Improvement Attempt SN010.jpgSN010_D980454-00-C.pdfSN010_Notch_Improvement_Attempt.pdf
                Reply  Thu Jan 16 20:18:44 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN010 (South RFPD) Notch Improved SN010.jpgSN010_D980454-00-C.pdfSN010_Notch_Improved.pdf
                   Reply  Mon Jan 27 18:29:19 2020, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Out Spectrum FSS_RFPD_RFOut_Spectrum.pdf
Message ID: 2490     Entry time: Mon Dec 9 19:54:44 2019     In reply to: 2481
Author: anchal 
Type: DailyProgress 
Category: FSS 
Subject: FSS Diagnostics - How much distortion affects the functioning of PDH? 

I'm trying to think hard with my small brain how the distortion would affect the PDH functioning and inject noise in the frequency of the laser. I have a line of reasoning which starts with a question.:

  • The two RF sidebands of laser that fall on the cavity, upon reflection, do they destructively interfere? Because the calculation I did in CTN:2481 suggests that the power at second harmonic (2-Omega frequency) is so high because of the sidebands beating with each other.
  • In case they do not destructively interfere, the generated second-order harmonic (2-Omega) will have laser amplitude noise on it. This when it mixes with the (1-Omega) signal which actually carries the cavity length noise at the inputs of MAX4107, the distorted 1-Omega created would have laser amplitude noise on it.
  • This might be the reason why FSS loops get overwhelmed with seeing a lot of laser amplitude noise which ideally it is not supposed to see. And it tries to correct this noise in phase quadrature making the situation worse.
  • Since Andrew left, I increased the laser power reaching the cavities to go above the shot-noise limit of the photodiodes. Maybe, this increased light level increased this effect to a point where we are witnessing the problem.

Of course, all this depends on the RF sidebands interfering constructively upon reflection. I remember (I don't know from where) that it is the opposite. Either there is a fault in my calculations or this is indeed what is happening. I need to understand this properly to go further. Need help.

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