As it was found that AA loop is introducing locking accuracy problem (elog2227), and I also tried to reduce the coupling from y/p to l(the improvement is mainly the coupling from y to l) (elog2229).

After that I did the comparison in the following three different situations:

1. No AA loop but local control engaged for input/end mirrors.

2. With the same AA loop (compared with elog2227)

3. With AA loop but the gain of yaw control was increased by a factor of 10 for end mirror, the gain of end/input mirror pitch were increased by a factor of 2.

The comparison is shown in the attached figure 1.

1.According to the transfer function of INPUT/END pitch (figure 2, 3), it seems the resonance around 8 and 9Hz is feed back a lot. But according to the transfer function of INPUT/END yaw (figure 4, 5), it seems the resonance around 1.45Hz is only obvious in the orange line.

2. By checking the noise spectrum of each mirror motion, the new peak in orange line around 6.5Hz should come from the Pitch/Yaw of PR.

3. By checking the noise spectrum, the orange ~3Hz peak's reduction may be due to END mirror pitch is controlled better. The orange ~5Hz peak's reduction maybe due to INPUT mirror pitch is controlled better.

Note that: the green and blue lines were measured within almost 5mins. But the organge line was measured almost 4hours later.