I downloaded a segment of data from the time when the DRMI was locked with the BS and ITM coil driver de-whitening switched on, and looked at coherence between MC transmission and the MICH error signal. Attachment #1 doesn't show any broadband high coherence between 60-300Hz, so it cannot explain the noise in the full range between 60-300Hz.
The DQ channel for the MC transmission is recorded at 1024 kHz, so to calculate the coherence, I had to decimate the 16K MICH data.
Since we have the AOM installed, I suppose we can actually measure the intensity noise coupling to MICH by driving a line in the AOM.
I also checked for coherence in the 60-300Hz band between MICH/PRCL and MICH/SRCL, and didn't see any appreciable coherence. Need to think about this more.
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Rana suggested checking coherence with MC transmission to see if this could be laser intensity noise.
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