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Entry  Thu Aug 22 00:29:32 2013, tara, DailyProgress, NoiseBudget, installed EOAM EOAM.jpgnb_short_cav.png
    Reply  Thu Aug 22 20:31:28 2013, tara, DailyProgress, NoiseBudget, installed EOAM nb_short_cav.pngnb_short_cav.figRFAM.jpg
Message ID: 1311     Entry time: Thu Aug 22 20:31:28 2013     In reply to: 1309
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: installed EOAM 

The bump at 2kHz in the beat signal that I saw before was also from RFAM. By adjusting the 1/2 waveplate in front of the sideband EOM, the bump disappears. I still don't understand why adjusting the EOAM can reduce the bump from RFAM.

 As I planned to add the eom driver to the BB EOM for sideband in RCAV path, I wanted to see the improvement without worrying about the EOAM optimzation. So I removed the EOAM, but I still saw the bump I observed before. This time it came from the RFAM. By adjusting the wave plate to match the polarization of the input beam to the EOM axis, the bump is gone.

RFAM.jpg

above: From right to left, 1) laser for RCAV, 2)&3) 1/2 and 1/4 wave plates, 4) lense, 5) Faraday isolator, 6) 1/2 wave plate, 7)BB EOM for frequency locking, 8) BB EOM for side band, the EOM driver is attached to the side (in aluminum foil wrapped box). RFAM is minimized by adjusting (6) 1/2 wave plate.

I added the EOM driver, however it was not yet modified for 14.75 MHz, so the amplification is small, see PSL:1234 . After adjusting the phase of the demodulated sigmal, the error signal slope is increased by a factor of 2. Then I remeasured the beat signal, and the beat was better by ~ a factor of 2 at high frequency. So I think now the signal is gain limited (in RCAV loop) at high frequency. This makes me confused why the error noise from RCAV loop does not match the beat signal in PSL:1307. I have to re check my work.

 nb_short_cav.png

The next few things to do are:

  • minimize RFAM (by temp control on both EOMs )
  • re-install EOAM in RCAV path, think about alignment
  • now scattered light at low frequency might come from seismic noise as well. I'll order the new floating table legs soon.
  • check other noise limit to make sure that it will not be dominating (shot noise, electronic noise)
  • modify the EOM driver, so that we have more gain in RCAV path.

 

 

Attachment 2: nb_short_cav.fig  185 kB  Uploaded Fri Aug 23 00:50:39 2013
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