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Entry  Fri Jan 4 19:04:29 2019, awade, DailyProgress, RFAM, Time to look at RF AM and RIN 
    Reply  Wed Jan 9 17:25:38 2019, anchal, DailyProgress, RFAM, Time to look at RF AM and RIN RIN_DBN_Coherence_Measurement.pdf
       Reply  Wed Jan 9 19:05:56 2019, anchal, DailyProgress, RFAM, Time to look at RF AM and RIN 
          Reply  Thu Jan 10 11:38:53 2019, awade, DailyProgress, RFAM, Time to look at RF AM and RIN 
             Reply  Thu Jan 10 17:30:24 2019, anchal, DailyProgress, RFAM, Time to look at RF AM and RIN 
                Reply  Thu Jan 10 18:52:20 2019, anchal, DailyProgress, RFAM, Time to look at RF AM and RIN 
                   Reply  Sat Jan 12 13:11:02 2019, awade, DailyProgress, RFAM, Time to look at beatnote after RF AM and RIN tuneup 
                      Reply  Wed Jan 16 11:07:41 2019, anchal, DailyProgress, NoiseBudget, Beatnote after RF AM and RIN tuneup LaserPowerNoise_to_BNFreqNoise_TF.pdfIN_to_BN_TF.zipTransmission_RIN_Jan15_2019.pdfRIN_Measurement_20190115.zip20190116_130937noiseBudget.pdf
    Reply  Thu Jan 10 14:19:46 2019, anchal, DailyProgress, RFAM, Time to look at RF AM and RIN 
Message ID: 2282     Entry time: Sat Jan 12 13:11:02 2019     In reply to: 2281     Reply to this: 2283
Author: awade 
Type: DailyProgress 
Category: RFAM 
Subject: Time to look at beatnote after RF AM and RIN tuneup 

Nice.  

It would be a good time to retake the BN + cross spectrum with RIN to see if these improvements squash the 3 kHz hump.  You'll probably want to recheck the RFAM levels immediately before retaking the BN in case there has been any drift.  When plotting the RIN you should include a trace that quantifies the dark noise of the PDs and the shot noise. The traces are not much use if they are limited by either of these, the elog readers would benefit from having such traces as a bench mark.

A good thing to do, as well, would be to resurrect the AEOM power controls in both paths.  You can then use a swept sine to take a transfer function from intensity noise to beat note directly without just relying on the residual RIN of the laser*.  This will help you model the expected real TF from intensity noise to frequency noise (for the noise budget) and help justify the design choices of the ISS (how far along is the ISS BTW?).  It also lets you know the susceptibility of each path to RIN, regardless of the performance differences between the two laser.  Maybe its also possible to fine tune the offsetting on the FSS PDH controls by watching the transfer function live and adjusting the DC offset to minimize Intensity->FSS->Freq Noise conversion.  The offsets and gains on the FSS loop are now more or less arbitrary, this is something you can try next time you tweak up these loops.

THe AEOMs should be configured with s-polarized light (vertical) going into the modulator with a quarter-wave plate, followed by a PBS at the output.  Adjust the quarter-wave plate to get yourself to 50:50 splitting, this gives you the maximum W/V slope with close to linear response. You'll need to adjust upstream powers accordingly to give you 1.5 mW at the input of the RefCavs. Be aware of how hard you are driving the modulators so that you are sure that it is in the linear regime.  Terminate AEOMs when not in use. 


* It would also be nice to have a tap off somewhere (<10%) to be able to sample the pre-cavity RIN.  Given that any BS/ wedge you insert will misaligned the beams it will be a 0.5 day exercise to realign cavities etc, thus mid-low priority.

 

Quote:

I think I found the culprit. the polarizer behind the EOM (PMC loop EOM) was a multi-order one and hence was extremely sensitive to temperature. I replaced it with a zero order half wavepleate and realigned the EOM to minimise the RF AM to about -70 dBm. The PMC has got misaligned in this procedure, so tomorrow I'll align it back and see if our changes made a difference.

 

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