Eleonora, Yaochin, and Yuhang

Firstly, we tried to excite FC length by using H1 and H3 coil. But we found H1 is not working(because we sent excitation to H1 only but the mirror couldn't move accordingly). So we checked if we were sending the signal and whether the signal is reaching the coil driver. We found the signal is reaching the coil driver but with some noise. The frequency of this noise is measured as 700kHz.

So we decided to excited FC length by using H2 and H4 coil. The method we used to diagonalize is to measure the response of the mirror optical lever signal. We sent excitation to channel K1:FDS-INPUT_Z_CORR_fil_EXC with a frequency of 4Hz and amplitude of 4000. We set the matrix index for H2 as 1 and measured the spectrum of K1:FDS-INPUT_Y_fil_IN1. There was a peak of 126.9 at 4Hz. Then we set the matrix index for H4 as 1 and measured the spectrum of K1:FDS-INPUT_Y_fil_IN1. There was a peak of 173.4 at 4Hz. So we decide to put index 1 for H2 while index 0.73 for H4 to make the coupling to yaw to be zero.

In the end, we measured the transfer function from the excitation of the INPUT mirror length to FC correction. There should be a response. We also measured the TF from the excitation of INPUT mirror length to INPUT mirror yaw optical lever. There should be not a response. Also the coherence of the above two. The result is shown in the attached figure 1. We have a response from the FC correction signal 10 times larger than the response from the yaw optical lever. Also, the coherence is better for FC correction. This can be a good start for the implementation of the feedback for CC2 phase noise.