I calibrated the CARM error signal (K1:LSC-CARM_RESIDUAL_IN1) by using the actuator efficiency obtained in privious post. Enable the CARMIN2 SW and excite the CARM loop via DGCARM. Then, measure the TF from K1:CAL-CS_PROC_CARM_FILT_AOM_OUT to K1:LSC-CARM_RESIDUAL_IN1. The response of LPF is included into K1:LSC-CARM_RESIDUAL_IN1 by calibrating it with zpk(0,[],1) The result is shown in the attached figure.  I put the inverse of optical gain in K1:LSC-CARM_RESIDUAL, so the output of this filter is now calibrated in Hz.

I excited CARM again, and then measure the CARM to DARM coupling

Then, I measured the CARM to DARM coupling.

The attached figure shows the coupling. In HF range, the coupling is 10^-14 m/Hz. It was difficult to have coherence in LF range.