I again measured the frequency noise coupling into DARM by injecting at the common-mode error point. This time, I did both a broadband injection and a swept-sine injection. The broadband TF is shown in the second attachment.

Compared to the previous measurement (2015-10-08, first attachment), the high frequency coupling seems to have decreased by a factor of 3.

Combined with the expected residual frequency noise (third attachment), this suggests that frequency noise lies a factor of 50 to 100 below the DCPD shot noise (1×10⁻⁷ mA/Hz^1/2).