IFO_REFL_HWP +160, with CARM UGF~50kHz and phase margin ~ 32 deg
I precisely measured the CARM OLTF around 50 kHz with 16W PRFPMI with the REFL HWP angle of 160 degrees.
Figure 1 shows the results
The peak around 50kHz exceeds a gain of 0 dB, and the phase margin at UGF is only 14 degrees, which is too small.
So, I changed the REFL HWP angle from 160 to 161 degrees and measures the OLTF again (fig2).
The peak around 50kHz somehow became lower and it no longer exceeds 0 dB, so this setting should be fine.
Figure 3 shows the OLTF of the CARM loop from 10 kHz to 100 kHz with REFL HWP angle of 161 degrees.
The UGF is 41 kHz and the phase margin is 40 degrees, which seems robust enough.
