C. Hirose, K. Tanaka

We measured the response at each QPD (REFL WFS1,2, MCE TRANS DCQPD1, 2, IMMT1 TRANS DCQPD1)when we actuated each actuator (MCI, MCO, MCE, COMMON, DIFFERENTIAL between MCI and MCO) and summarized these results in form of the matrices. 

PIT

YAW

Based on these matrices, we obtained the combination of sensors with the highest sensitivity to the motion of each actuator. To start with, we created sensors that are sensitive to the each angular fluctuation of the MCE. Looking at the MCE TRANS QPD row of the above matrices, we can see that the motion of the MCE in the YAW direction can be obtained by adding MCE TRANS DCQPD1 and 2 together at 1:0.85. Similarly, for MCE movement in the PIT direction, MCE TRANS DCQPD1 and 2 should be added together at a ratio of 0.3 to 1.

We created control loops to control the each angular fluctuation of the MCE using these sensors. Figs. 1 and 2 show the open-loop transfer functions of the control loop for the MCE in the PIT and yaw directions, respectively. The bottom right of these figures show the spectra of the in-loop sensor and oplev during control on/off. As far as we can see, in the pitch case the noise on the high frequency side needs to be reduced a little more, and in the yaw case, the noise on the high frequency side is returning the noise and making the yaw sway a little more, so we need to review the filter design.