Following alog 19856 we took the same coherence measurements (OMC_DCPDs vs AS_C_LF vs AS_A_RF36) in different configurations.

a)  Plot 1: we locked the OMC on a 45MHz SB at 15W of input power (to avoid PD saturation). In this configuration we retook the coherence measurement between AS_C_LF and OMC_DC, as well as AS_A_RF36 and OMC_DC. (Also, the ISS was off in this state)
 - While we see coherence above 2Hz - similar to that in alog 19856 - nothing is visible below that.
 - In the power spectrum of the side band we can identify two features:
   - At 19032Hz we see the effect of the sideband 00 mode going through arm resonance
     (actually, we are seeing the peak in between where the lower and upper audio sideband goes through resonance - resulting in maximum FM to AM conversion in between)
   - Similarly, at 9700Hz we see the feature that corresponds to the sideband 02 mode going through resonance.
     This might we a way to fine-tweak the PRC to ARM mode-matching when we do common CO2 heating runs.

b) Plot 2: comparing ISS_SECONDLOOP_GAIN at 25dB (dashed coherence) vs 0dB (solid coherence)
 - The 14kHz gain peaking of the ISS clearly shows up, but below ~8kHz there is no obvious change
 - for 25dB we estimate the UGF to be at 3kHz
 - for  0dB we estimate the UGF to be around a few 100Hz.

c) Plot 3: comparing FSS_COMMON_GAIN at 20.7dB vs 14.7dB
 - I do not see any difference in the coherence.