40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
 List  |  Find  |  Login  |  Help 
Entry  Mon Sep 2 03:38:27 2013, tara, DailyProgress, NoiseBudget, beat zoom_beat_2013_09_02.pngbeat_2013_09_02.pngnb_short_cav.figzoom_beat_2013_09_02.png
    Reply  Tue Sep 3 09:52:17 2013, rana, DailyProgress, NoiseBudget, Seismic Noise Coupling 
       Reply  Wed Sep 4 18:40:00 2013, rana, DailyProgress, NoiseBudget, Seismic Noise Coupling 
    Reply  Sat Sep 7 04:29:32 2013, tara, DailyProgress, NoiseBudget, beat 
       Reply  Mon Sep 9 02:27:46 2013, tara, DailyProgress, NoiseBudget, RIN induced TO noise in beat 6x
          Reply  Mon Sep 9 21:19:24 2013, tara, DailyProgress, NoiseBudget, RIN induced TO noise in beat RIN_ACAV.pngRIN_ACAV.figbenid_ACAV.jpgfront_ACAV.jpg
             Reply  Tue Sep 10 04:53:34 2013, tara, DailyProgress, NoiseBudget, RIN induced TO noise in beat 
Message ID: 1329     Entry time: Mon Sep 9 02:27:46 2013     In reply to: 1327     Reply to this: 1331
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: RIN induced TO noise in beat 

The measured RIN is measured and converted to frequency noise via photo thermal effect then compared to beat. The effect seems to be significant now since we lost the common mode rejection.

I measured RIN after ACAV (there is only one PD behind ACAV right now. we will add another one for RCAV soon). The magnitude is comparable from what we measured before but the peaks seem to change, see PSLPSL:1326, :PSL:1308,  (8"cavity) PSL:742 .

ACAV_RIN.png

The peaks around kHz  are more clear. I'm not sure where they are from, but I think it is associated with vibration on mirror mounts that causes beam jitter. Because the peaks look like mechanical peaks, and this time the cavities are shorter, the beamsize is smaller from 8" cavities, the same beam misalignment will cause the power coupled into the cavities to change more compared to that of 8" cavity. We can check that by mis-aligning the input beam a bit, and see if RIN becomes larger or not.

The coupling from RIN to frequency noise is discussed in PSL:1328

I applied that to the measurement and here is the result. Note, only the effect from one cavity (ACAV) is taken into account.

beat_2013_09_06.png

The peaks seems to match up, especially around 20-30Hz and around 1kHz, see the zoomed in picture below. This makes me think that we might be limited by RIN noise now.

rin_noise.png

 

To Do next:

  • Install ISS system on RCAV (PD behind the cavity / EOAM)
  • Re-measure the coupling from RIN to frequency noise of the cavity
  • Measure RIN and apply it to the noise budget.
  • Find out what causes RIN to change
Attachment 2: rin_noise.fig  162 kB  Uploaded Mon Sep 9 03:42:49 2013
Attachment 4: ACAV_RIN.fig  29 kB  Uploaded Mon Sep 9 04:02:44 2013
Attachment 5: beat_2013_09_06.fig  203 kB  Uploaded Mon Sep 9 04:19:59 2013
ELOG V3.1.3-