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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: 1321     Entry time: Mon Sep 2 03:38:27 2013     Reply to this: 1323   1327
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: beat 

It's a quiet night, so I went down the lab to measure the beat signal. We are getting close. I think I have to review my noise budget calculation and estimate the error in the measurement carefully.

So after a few things Evan and I did a few days ago:

  1. rotate the stack to get rid off the reflected beam from the window
  2. fix the insulation so the beam is not clipped on the opening.
  3. add more modulation depth to RCAV path with the EOM driver (tuned to 14.75MHz)
  4. Minimize some RFAM, by rotating the half wave plate in front of the sideband EOM

Then I measured the beat signal.

We reduce some noise from scattered light at frequency below 100 Hz, we are limited by some white noise at high frequency ~ above 1 kHz.

beat_2013_09_02.png

fig1: measurement vs noise budget

zoom_beat_2013_09_02.png

fig2: zoom in. The slope of the measured signal agrees well with the slope of thermal noise.

ToDo

  • Estimate/measure shot noise PD noise and electronic noise in the setup. See if they match up with the measurement.
  • Review the noise budget calculation. Looking at the slope of the signal around 1kHz, I think the calculated brownian noise is lower than what it should be.
  • noise hunting, seems like scattered light at frequency below 100Hz. There are many mechanical peaks, and harmonic lines at higher frequency.
  • add the contribution from RIN induced TO noise in the nb.
Attachment 1: zoom_beat_2013_09_02.png  39 kB  | Hide | Hide all
zoom_beat_2013_09_02.png
Attachment 3: nb_short_cav.fig  195 kB
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