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Message ID: 2378     Entry time: Mon Jul 29 13:55:15 2019
Author: anchal 
Type: DailyProgress 
Category: FSS 
Subject: Noise analysis of TTFSS 


  • I first switched the input to TTFSS from PD to Test1. There is a switch which lets us do this. This bypasses the onboard mixer.
  • I set the COM gain in both boxes to 10 dB and FAST gain to 14 dB.
  • I shorted this Test1 port and measured the noise spectrum at the output ports that go to Laser PZT and EOM.
  • The spectrum was taken by WideSpecMeasSR.py, a new modified version fo SRmeasure script. This script starts taking spectrum from startFreq and spanFreq and continues doing measurement by shifting startFreq up and doubling the span to get a consistent number of points with good linewidth in each decade of frequency.
  • Next, I measured transfer functions from the Test1 port to these output ports using various attenuators to make sure the measurement doesn't saturate.
  • The measurement parameter files are attached and the attenuator configuration is mentioned in the notebook.

Analysis and Conclusions:

  • I divided the measured output noise with respective transfer functions to get the input-referred noise.
  • I did this so that we can compare the noises on the same scale.
  • It seems like the South Path's TTFSS is noisier on both actuation channels. Note that the gains were set same, so there is actually a difference in gain values and noise.
  • Input referred noise shows that North PZT path is the noisiest followed by South PZT path. I'll go noise hunting on these paths first then.
  • Also, we see clear 60, 180, 300, 420, 540, 780,900 and 1020 Hz (660 Hz is missing) peaks in the input-referred noise of North PZT output path.
  • Additionally, there are comparatively smaller peaks of 120 Hz and 240 Hz also present in North PZT output path.
  • On South path though, the peaks are lower and are present at 60, 180, 300, 780 and 900 Hz only.

Code and Data

Attachment 1: FSSNoiseAndTFAnalysis.pdf  421 kB  Uploaded Mon Jul 29 15:26:15 2019  | Hide | Hide all
FSSNoiseAndTFAnalysis.pdf FSSNoiseAndTFAnalysis.pdf FSSNoiseAndTFAnalysis.pdf
Attachment 2: FSSNoiseAndTFAnalysis.zip  1.103 MB  Uploaded Mon Jul 29 15:45:18 2019
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