Yuhang and Aritomi

We tried to put a rubber at the place where we think it can be related to resonance. First, we tried to put it between mirror/PZT holder and mirror mount. See attached figure 1 and 2.

In the measurement shown in entry 1503, CC1 has already been installed with this rubber while not for CC2. In this entry, I put a comparison of OLTF for CC2 with and without the rubber.

In the attached figure 3, it is shown the measurement with and without the rubber. We can see 4kHz resonance is damped.

In the attached figure 4, I add 12dB to measurement with rubber. The reason is we were locking with different unity gain frequency. In this case, we could compare better. From this comparison, we could see that the reduction of resonance at 4kHz gives energy to the peak at 600Hz and 7kHz and makes them higher.

Considering the position we put rubber, we think 4kHz corresponds to resonance along the direction of mirror/PZT holder axis.