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Mon Jul 29 13:55:15 2019
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
, 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.
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
Uploaded Mon Jul 29 15:26:15 2019
Uploaded Mon Jul 29 15:45:18 2019